Publications by authors named "David A Long"

74 Publications

Mechanisms and cell lineages in lymphatic vascular development.

Angiogenesis 2021 Apr 6. Epub 2021 Apr 6.

UCL Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK.

Lymphatic vessels have critical roles in both health and disease and their study is a rapidly evolving area of vascular biology. The consensus on how the first lymphatic vessels arise in the developing embryo has recently shifted. Originally, they were thought to solely derive by sprouting from veins. Since then, several studies have uncovered novel cellular mechanisms and a diversity of contributing cell lineages in the formation of organ lymphatic vasculature. Here, we review the key mechanisms and cell lineages contributing to lymphatic development, discuss the advantages and limitations of experimental techniques used for their study and highlight remaining knowledge gaps that require urgent attention. Emerging technologies should accelerate our understanding of how lymphatic vessels develop normally and how they contribute to disease.
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http://dx.doi.org/10.1007/s10456-021-09784-8DOI Listing
April 2021

The Biological Significance and Implications of Planar Cell Polarity for Nephrology.

Front Physiol 2021 26;12:599529. Epub 2021 Feb 26.

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, London, United Kingdom.

The orientation of cells in two-dimensional and three-dimensional space underpins how the kidney develops and responds to disease. The process by which cells orientate themselves within the plane of a tissue is termed planar cell polarity. In this Review, we discuss how planar cell polarity and the proteins that underpin it govern kidney organogenesis and pathology. The importance of planar cell polarity and its constituent proteins in multiple facets of kidney development is emphasised, including ureteric bud branching, tubular morphogenesis and nephron maturation. An overview is given of the relevance of planar cell polarity and its proteins for inherited human renal diseases, including congenital malformations with unknown aetiology and polycystic kidney disease. Finally, recent work is described outlining the influence of planar cell polarity proteins on glomerular diseases and highlight how this fundamental pathway could yield a new treatment paradigm for nephrology.
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http://dx.doi.org/10.3389/fphys.2021.599529DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7952641PMC
February 2021

Pseudouridylation defect due to and mutations causes nephrotic syndrome with cataracts, hearing impairment, and enterocolitis.

Proc Natl Acad Sci U S A 2020 06 17;117(26):15137-15147. Epub 2020 Jun 17.

MTA-SE Lendület Nephrogenetic Laboratory, Semmelweis University, HU 1083 Budapest, Hungary;

RNA modifications play a fundamental role in cellular function. Pseudouridylation, the most abundant RNA modification, is catalyzed by the H/ACA small ribonucleoprotein (snoRNP) complex that shares four core proteins, dyskerin (DKC1), NOP10, NHP2, and GAR1. Mutations in , , or cause dyskeratosis congenita (DC), a disorder characterized by telomere attrition. Here, we report a phenotype comprising nephrotic syndrome, cataracts, sensorineural deafness, enterocolitis, and early lethality in two pedigrees: males with p.Glu206Lys and two children with homozygous p.Thr16Met. Females with heterozygous p.Glu206Lys developed cataracts and sensorineural deafness, but nephrotic syndrome in only one case of skewed X-inactivation. We found telomere attrition in both pedigrees, but no mucocutaneous abnormalities suggestive of DC. Both mutations fall at the dyskerin-NOP10 binding interface in a region distinct from those implicated in DC, impair the dyskerin-NOP10 interaction, and disrupt the catalytic pseudouridylation site. Accordingly, we found reduced pseudouridine levels in the ribosomal RNA (rRNA) of the patients. Zebrafish mutants recapitulate the human phenotype and show reduced 18S pseudouridylation, ribosomal dysregulation, and a cell-cycle defect in the absence of telomere attrition. We therefore propose that this human disorder is the consequence of defective snoRNP pseudouridylation and ribosomal dysfunction.
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http://dx.doi.org/10.1073/pnas.2002328117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7334496PMC
June 2020

Beyond a Passive Conduit: Implications of Lymphatic Biology for Kidney Diseases.

J Am Soc Nephrol 2020 06 15;31(6):1178-1190. Epub 2020 Apr 15.

Developmental Biology and Cancer Programme, Great Ormond Street Institute of Child Health, University College London, London, United Kingdom

The kidney contains a network of lymphatic vessels that clear fluid, small molecules, and cells from the renal interstitium. Through modulating immune responses and crosstalk with surrounding renal cells, lymphatic vessels have been implicated in the progression and maintenance of kidney disease. In this Review, we provide an overview of the development, structure, and function of lymphatic vessels in the healthy adult kidney. We then highlight the contributions of lymphatic vessels to multiple forms of renal pathology, emphasizing CKD, transplant rejection, and polycystic kidney disease and discuss strategies to target renal lymphatics using genetic and pharmacologic approaches. Overall, we argue the case for lymphatics playing a fundamental role in renal physiology and pathology and treatments modulating these vessels having therapeutic potential across the spectrum of kidney disease.
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http://dx.doi.org/10.1681/ASN.2019121320DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7269340PMC
June 2020

Endothelial-epithelial communication in polycystic kidney disease: Role of vascular endothelial growth factor signalling.

Cell Signal 2020 08 31;72:109624. Epub 2020 Mar 31.

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, London, UK. Electronic address:

Whereas targeting the cyst epithelium and its molecular machinery has been the prevailing clinical strategy for polycystic kidney disease, the endothelium, including blood vasculature and lymphatics, is emerging as an important player in this disorder. In this Review, we provide an overview of the structural and functional alterations to blood vasculature and lymphatic vessels in the polycystic kidney. We also discuss evidence for vascular endothelial growth factor signalling, otherwise critical for endothelial cell development and maintenance, as being a fundamental molecular pathway in polycystic kidney disease and a potential therapeutic target for modulating cyst expansion.
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http://dx.doi.org/10.1016/j.cellsig.2020.109624DOI Listing
August 2020

Free 25-hydroxyvitamin-D concentrations are lower in children with renal transplant compared with chronic kidney disease.

Pediatr Nephrol 2020 06 22;35(6):1069-1079. Epub 2020 Jan 22.

Renal Unit, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK.

Background: Total serum 25-hydroxyvitamin D [25(OH)D] is considered the best marker of vitamin D status and used routinely in clinical practice. However, 25(OH)D is predominantly bound to vitamin D-binding protein (VDBP), and it has been reported that the free-25(OH)D and 25(OH)D loosely bound to albumin fraction correlates better with clinical outcomes.

Methods: We assessed total-25(OH)D, measured free-25(OH)D, and calculated free-25(OH)D and their relationship with VDBP and biomarkers of mineral metabolism in 61 children (22 CKD 2-3, 18 dialysis, and 21 post-transplant).

Results: Total-25(OH)D concentrations were comparable across the three groups (p = 0.09), but free- and bioavailable-25(OH)D (free- and albumin-25(OH)D) were significantly lower in the transplant group (both: p = 0.01). Compared to CKD and dialysis patients, the transplant group had significantly higher VDBP concentrations (p = 0.03). In all three groups, total-25(OH)D concentrations were positively associated with measured free-, calculated free-, and bioavailable-25(OH)D. Multivariable regression analysis showed that total-25(OH)D was the only predictor of measured free-25(OH)D concentrations in the dialysis group (β = 0.9; R = 90%). In the transplant group, measured free-25(OH)D concentrations were predicted by both total-25(OH)D and VDBP concentrations (β = 0.6, - 0.6, respectively; R = 80%). Correlations between parathyroid hormone with total-25(OH)D and measured and calculated free-25(OH)D were only observed in the transplant group (all: p < 0.001).

Conclusions: In transplanted patients, VDBP concentrations were significantly higher compared to CKD and dialysis patients, and consequently, free-25(OH)D concentrations were lower, despite a comparable total-25(OH)D concentration. We suggest that free-25(OH)D measures may be required in children with CKD, dialysis, and transplant, with further research required to understand its association with markers of mineral metabolism.
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http://dx.doi.org/10.1007/s00467-020-04472-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7184055PMC
June 2020

Spatiotemporal dynamics and heterogeneity of renal lymphatics in mammalian development and cystic kidney disease.

Elife 2019 12 6;8. Epub 2019 Dec 6.

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, University College London, London, United Kingdom.

Heterogeneity of lymphatic vessels during embryogenesis is critical for organ-specific lymphatic function. Little is known about lymphatics in the developing kidney, despite their established roles in pathology of the mature organ. We performed three-dimensional imaging to characterize lymphatic vessel formation in the mammalian embryonic kidney at single-cell resolution. In mouse, we visually and quantitatively assessed the development of kidney lymphatic vessels, remodeling from a ring-like anastomosis under the nascent renal pelvis; a site of VEGF-C expression, to form a patent vascular plexus. We identified a heterogenous population of lymphatic endothelial cell clusters in mouse and human embryonic kidneys. Exogenous VEGF-C expanded the lymphatic population in explanted mouse embryonic kidneys. Finally, we characterized complex kidney lymphatic abnormalities in a genetic mouse model of polycystic kidney disease. Our study provides novel insights into the development of kidney lymphatic vasculature; a system which likely has fundamental roles in renal development, physiology and disease.
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http://dx.doi.org/10.7554/eLife.48183DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6948954PMC
December 2019

Generating Mutant Renal Cell Lines Using CRISPR Technologies.

Methods Mol Biol 2020 ;2067:323-340

Genetics and Genomic Medicine Programmes, Great Ormond Street Institute of Child Health, University College London, London, UK.

Gene editing using the CRISPR/Cas9 system is an extremely efficient approach for generating mutations within the genomic DNA of immortalized cell lines. This procedure begins with a straightforward cloning step to generate a single plasmid encoding the Cas9 enzyme as well as a synthetic guide RNA (sgRNA) which is selected to target specific sites within the genome. This plasmid is transfected into cells either alone, in order to generate random insertion-deletion alleles ("indels") at the desired locus via the nonhomologous end-joining pathway, or in conjunction with a homology-directed repair template oligonucleotide to generate a specific point mutation. Here we describe a procedure to perform gene editing in IMCD3 and HEK293 cells and to subsequently isolate clonal cell lines carrying mutations of interest.
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http://dx.doi.org/10.1007/978-1-4939-9841-8_20DOI Listing
December 2020

Tissue Clearing and Deep Imaging of the Kidney Using Confocal and Two-Photon Microscopy.

Methods Mol Biol 2020 ;2067:103-126

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, University College London, London, UK.

Microscopic and macroscopic evaluation of biological tissues in three dimensions is becoming increasingly popular. This trend is coincident with the emergence of numerous tissue clearing strategies, and advancements in confocal and two-photon microscopy, enabling the study of intact organs and systems down to cellular and sub-cellular resolution. In this chapter, we describe a wholemount immunofluorescence technique for labeling structures in renal tissue. This technique combined with solvent-based tissue clearing and confocal imaging, with or without two-photon excitation, provides greater structural information than traditional sectioning and staining alone. Given the addition of paraffin embedding to our method, this hybrid protocol offers a powerful approach to combine confocal or two-photon findings with histological and further immunofluorescent analysis within the same tissue.
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http://dx.doi.org/10.1007/978-1-4939-9841-8_8DOI Listing
December 2020

Using a Speed-Dependent Voigt Line Shape to Retrieve O from Total Carbon Column Observing Network Solar Spectra to Improve Measurements of XCO.

Atmos Meas Tech 2019 ;12

Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA, USA.

High-resolution, laboratory, absorption spectra of the oxygen (O) band measured using cavity ring-down spectroscopy were fitted using the Voigt and speed-dependent Voigt line shapes. We found that the speed-dependent Voigt line shape was better able to model the measured absorption coefficients than the Voigt line shape. We used these line shape models to calculate absorption coefficients to retrieve atmospheric total columns abundances of O from ground-based spectra from four Fourier transform spectrometers that are apart of the Total Carbon Column Observing Network (TCCON) Lower O total columns were retrieved with the speed-dependent Voigt line shape, and the difference between the total columns retrieved using the Voigt and speed-dependent Voigt line shapes increased as a function of solar zenith angle. Previous work has shown that carbon dioxide (CO) total columns are better retrieved using a speed-dependent Voigt line shape with line mixing. The column-averaged dry-air mole fraction of CO (XCO) was calculated using the ratio between the columns of CO and O retrieved (from the same spectra) with both line shapes from measurements made over a one-year period at the four sites. The inclusion of speed dependence in the O retrievals significantly reduces the airmass dependence of XCO and the bias between the TCCON measurements and calibrated integrated aircraft profile measurements was reduced from 1% to 0.4%. These results suggest that speed dependence should be included in the forward model when fitting near-infrared CO and O spectra to improve the accuracy of XCO measurements.
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http://dx.doi.org/10.5194/amt-12-35-2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6774361PMC
January 2019

Twenty-Five-Fold Reduction in Measurement Uncertainty for a Molecular Line Intensity.

Phys Rev Lett 2019 Jul;123(4):043001

National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.

To accurately attribute sources and sinks of molecules like CO_{2}, remote sensing missions require line intensities (S) with relative uncertainties u_{r}(S)<0.1%. However, discrepancies in S of ≈1% are common when comparing different experiments, thus limiting their potential impact. Here we report a cavity ring-down spectroscopy multi-instrument comparison which revealed that the hardware used to digitize analog ring-down signals caused variability in spectral integrals which yield S. Our refined approach improved measurement accuracy 25-fold, resulting in u_{r}(S)=0.06%.
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http://dx.doi.org/10.1103/PhysRevLett.123.043001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6767615PMC
July 2019

Overexpression of Circulating Soluble Nogo-B Improves Diabetic Kidney Disease by Protecting the Vasculature.

Diabetes 2019 09 19;68(9):1841-1852. Epub 2019 Jun 19.

School of Cardiovascular Medicine & Sciences, British Heart Foundation Centre of Research Excellence, King's College London, London, U.K.

Damage to the vasculature is the primary mechanism driving chronic diabetic microvascular complications such as diabetic nephropathy, which manifests as albuminuria. Therefore, treatments that protect the diabetic vasculature have significant therapeutic potential. Soluble neurite outgrowth inhibitor-B (sNogo-B) is a circulating N-terminus isoform of full-length Nogo-B, which plays a key role in vascular remodeling following injury. However, there is currently no information on the role of sNogo-B in the context of diabetic nephropathy. We demonstrate that overexpression of sNogo-B in the circulation ameliorates diabetic kidney disease by reducing albuminuria, hyperfiltration, and abnormal angiogenesis and protecting glomerular capillary structure. Systemic sNogo-B overexpression in diabetic mice also associates with dampening vascular endothelial growth factor-A signaling and reducing endothelial nitric oxide synthase, AKT, and GSK3β phosphorylation. Furthermore, sNogo-B prevented the impairment of tube formation, which occurred when human endothelial cells were exposed to sera from patients with diabetic kidney disease. Collectively, these studies provide the first evidence that sNogo-B protects the vasculature in diabetes and may represent a novel therapeutic target for diabetic vascular complications.
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http://dx.doi.org/10.2337/db19-0157DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706276PMC
September 2019

SGLT2 Inhibitor, Canagliflozin, Attenuates Myocardial Infarction in the Diabetic and Nondiabetic Heart.

JACC Basic Transl Sci 2019 Feb 30;4(1):15-26. Epub 2019 Jan 30.

The Hatter Cardiovascular Institute, University College London, London, United Kingdom.

The authors hypothesized that despite similar cardiovascular event rates, the improved cardiovascular survival from sodium glucose transporter 2 (SGLT2) inhibition, seen clinically, could be via a direct cytoprotective effect, including protection against myocardial ischemia/reperfusion injury. Langendorff-perfused hearts, from diabetic and nondiabetic rats, fed long-term for 4 weeks with canagliflozin, had lower infarct sizes; this being the first demonstration of canagliflozin's cardioprotective effect against ischemia/reperfusion injury in both diabetic and nondiabetic animals. By contrast, direct treatment of isolated nondiabetic rat hearts with canagliflozin, solubilized in the isolated Langendorff perfusion buffer, had no impact on infarct size. This latter study demonstrates that the infarct-sparing effect of long-term treatment with canagliflozin results from either a glucose-independent effect or up-regulation of cardiac prosurvival pathways. These results further suggest that SGLT2 inhibitors could be repurposed as novel cardioprotective interventions in high-risk cardiovascular patients irrespective of diabetic status.
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http://dx.doi.org/10.1016/j.jacbts.2018.10.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6390729PMC
February 2019

Arterial "inflammaging" drives vascular calcification in children on dialysis.

Kidney Int 2019 04 1;95(4):958-972. Epub 2019 Mar 1.

British Heart Foundation Centre of Excellence, Cardiovascular Division, King's College London, London, UK. Electronic address:

Children on dialysis have a cardiovascular mortality risk equivalent to older adults in the general population, and rapidly develop medial vascular calcification, an age-associated pathology. We hypothesized that premature vascular ageing contributes to calcification in children with advanced chronic kidney disease (CKD). Vessels from children with Stage 5 CKD with and without dialysis had evidence of increased oxidative DNA damage. The senescence markers p16 and p21 were also increased in vessels from children on dialysis. Treatment of vessel rings ex vivo with calcifying media increased oxidative DNA damage in vessels from children with Stage 5 CKD, but not in those from healthy controls. Vascular smooth muscle cells cultured from children on dialysis exhibited persistent DNA damage, impaired DNA damage repair, and accelerated senescence. Under calcifying conditions vascular smooth muscle cells from children on dialysis showed increased osteogenic differentiation and calcification. These changes correlated with activation of the senescence-associated secretory phenotype (SASP), an inflammatory phenotype characterized by the secretion of proinflammatory cytokines and growth factors. Blockade of ataxia-telangiectasia mutated (ATM)-mediated DNA damage signaling reduced both inflammation and calcification. Clinically, children on dialysis had elevated circulating levels of osteogenic SASP factors that correlated with increased vascular stiffness and coronary artery calcification. These data imply that dysregulated mineral metabolism drives vascular "inflammaging" by promoting oxidative DNA damage, premature senescence, and activation of a pro-inflammatory SASP. Drugs that target DNA damage signaling or eliminate senescent cells may have the potential to prevent vascular calcification in patients with advanced CKD.
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http://dx.doi.org/10.1016/j.kint.2018.12.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6684370PMC
April 2019

Electro-optic frequency combs generated via direct digital synthesis applied to sub-Doppler spectroscopy.

OSA Contin 2019 ;2(12)

National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.

Direct digital synthesis in concert with an electro-optic phase modulator was employed to generate optical frequency combs with tooth spacings as low as 100 Hz. These combs were utilized to probe electromagnetically induced transparency (EIT) and hyperfine pumping in potassium vapor cells. Long-term coherent averaging was demonstrated with performance similar to that achieved with a vastly more expensive arbitrary waveform generator. From the potassium EIT transition we were able to determine the ground state hyperfine splitting with a fit uncertainty of 80 Hz. Importantly, because of the mutual coherence between the control and probe beams, which originate from a single laser, features with linewidths several orders-of-magnitude narrower than the laser linewidth could be observed in a multiplexed fashion. This approach removes the need for slow scanning of a traditional cw laser or mode-locked-laser-based optical frequency comb.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7448616PMC
January 2019

Vangl2, a planar cell polarity molecule, is implicated in irreversible and reversible kidney glomerular injury.

J Pathol 2018 12;246(4):485-496

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, London, UK.

Planar cell polarity (PCP) pathways control the orientation and alignment of epithelial cells within tissues. Van Gogh-like 2 (Vangl2) is a key PCP protein that is required for the normal differentiation of kidney glomeruli and tubules. Vangl2 has also been implicated in modifying the course of acquired glomerular disease, and here, we further explored how Vangl2 impacts on glomerular pathobiology in this context. Targeted genetic deletion of Vangl2 in mouse glomerular epithelial podocytes enhanced the severity of not only irreversible accelerated nephrotoxic nephritis but also lipopolysaccharide-induced reversible glomerular damage. In each proteinuric model, genetic deletion of Vangl2 in podocytes was associated with an increased ratio of active-MMP9 to inactive MMP9, an enzyme involved in tissue remodelling. In addition, by interrogating microarray data from two cohorts of renal patients, we report increased VANGL2 transcript levels in the glomeruli of individuals with focal segmental glomerulosclerosis, suggesting that the molecule may also be involved in certain human glomerular diseases. These observations support the conclusion that Vangl2 modulates glomerular injury, at least in part by acting as a brake on MMP9, a potentially harmful endogenous enzyme. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.
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http://dx.doi.org/10.1002/path.5158DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6282744PMC
December 2018

Planar cell polarity in organ formation.

Curr Opin Cell Biol 2018 12 14;55:96-103. Epub 2018 Jul 14.

Inflammation, Repair and Development Section, National Heart and Lung Institute, Imperial College, London, UK. Electronic address:

The planar cell polarity (PCP) pathway controls a variety of morphological events across many species. During embryonic development, the PCP pathway regulates coordinated behaviour of groups of cells to direct morphogenetic processes such as convergent extension and collective cell migration. In this review we discuss the increasingly prominent role of the PCP pathway in organogenesis, focusing on the lungs, kidneys and heart. We also highlight emerging evidence that PCP gene mutations are associated with adult diseases.
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http://dx.doi.org/10.1016/j.ceb.2018.06.011DOI Listing
December 2018

Thymosin-β4: A key modifier of renal disease.

Expert Opin Biol Ther 2018 07 9;18(sup1):185-192. Epub 2018 May 9.

b Developmental Biology and Cancer Programme , UCL Institute of Child Health , London , UK.

Introduction: There is an urgent need for new treatments for chronic kidney disease (CKD). Thymosin-β4 is a peptide that reduces inflammation and fibrosis and has the potential to restore endothelial and epithelial cell injury, biological processes involved in the pathophysiology of CKD. Therefore, thymosin-β4 could be a novel therapeutic direction for CKD.

Areas Covered: Here, we review the current evidence on the actions of thymosin-β4 in the kidney in health and disease. Using transgenic mice, two recent studies have demonstrated that endogenous thymosin-β4 is dispensable for healthy kidneys. In contrast, lack of endogenous thymosin-β4 exacerbates mouse models of glomerular disease and angiotensin-II-induced renal injury. Administration of exogenous thymosin-β4, or its metabolite, Ac-SDKP, has shown therapeutic benefits in a range of experimental models of kidney disease.

Expert Opinion: The studies conducted so far reveal a protective role for thymosin-β4 in the kidney and have shown promising results for the therapeutic potential of exogenous thymosin-β4 in CKD. Further studies should explore the mechanisms by which thymosin-β4 modulates kidney function in different types of CKD. Ac-SDKP treatment has beneficial effects in many experimental models of kidney disease, thus supporting its potential use as a new treatment strategy.
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http://dx.doi.org/10.1080/14712598.2018.1473371DOI Listing
July 2018

Lithium induces mesenchymal-epithelial differentiation during human kidney development by activation of the Wnt signalling system.

Cell Death Discov 2018 Dec 7;4:13. Epub 2018 Feb 7.

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, London, UK.

Kidney function is directly linked to the number of nephrons which are generated until 32-36 weeks gestation in humans. Failure to make nephrons during development leads to congenital renal malformations, whilst nephron loss in adulthood occurs in progressive renal disease. Therefore, an understanding of the molecular processes which underlie human nephron development may help design new treatments for renal disease. Mesenchyme to epithelial transition (MET) is critical for forming nephrons, and molecular pathways which control rodent MET have been identified. However, we do not know whether they are relevant in human kidney development. In this study, we isolated mesenchymal cell lines derived from human first trimester kidneys in monolayer culture and investigated their differentiation potential. We found that the mesenchymal cells could convert into osteogenic, but not adipogenic or endothelial lineages. Furthermore, addition of lithium chloride led to MET which was accompanied by increases in epithelial () and tubular () markers and downregulation of renal progenitor (, , ) and mesenchymal markers (, ). Prior to phenotypic changes, lithium chloride altered Wnt signalling with elevations in , GSK3β phosphorylation and β-catenin. Collectively, these studies provide the first evidence that lithium-induced Wnt activation causes MET in human kidneys. Therapies targeting Wnts may be critical in the quest to regenerate nephrons for human renal diseases.
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http://dx.doi.org/10.1038/s41420-017-0021-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5841285PMC
December 2018

In vivo three-dimensional photoacoustic imaging of the renal vasculature in preclinical rodent models.

Am J Physiol Renal Physiol 2018 06 20;314(6):F1145-F1153. Epub 2017 Dec 20.

Department of Medical Physics and Biomedical Engineering, University College London , London , United Kingdom.

Noninvasive imaging of the kidney vasculature in preclinical murine models is important for the assessment of renal development, studying diseases and evaluating new therapies but is challenging to achieve using existing imaging modalities. Photoacoustic imaging is a promising new technique that is particularly well suited to visualizing the vasculature and could provide an alternative to existing preclinical imaging methods for studying renal vascular anatomy and function. To investigate this, an all-optical Fabry-Perot-based photoacoustic scanner was used to image the abdominal region of mice. High-resolution three-dimensional, noninvasive, label-free photoacoustic images of the mouse kidney and renal vasculature were acquired in vivo. The scanner was also used to visualize and quantify differences in the vascular architecture of the kidney in vivo due to polycystic kidney disease. This study suggests that photoacoustic imaging could be utilized as a novel preclinical imaging tool for studying the biology of renal disease.
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http://dx.doi.org/10.1152/ajprenal.00337.2017DOI Listing
June 2018

Quantitative modeling of complex molecular response in coherent cavity-enhanced dual-comb spectroscopy.

J Mol Spectrosc 2018 ;352

Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, U.S.A.

We present a complex-valued electric field model for experimentally observed cavity transmission in coherent cavity-enhanced (CE) multiplexed spectroscopy (i.e., dual-comb spectroscopy, DCS). The transmission model for CE-DCS differs from that previously derived for Fourier-transform CE direct frequency comb spectroscopy [Foltynowicz et al., 163-175 (2013)] by the treatment of the local oscillator which, in the case of CE-DCS, does not interact with the enhancement cavity. Validation is performed by measurements of complex-valued near-infrared spectra of CO and CO by an electro-optic frequency comb coherently coupled to an enhancement cavity of finesse = 19600. Following validation, we measure the 30012 ← 00001 CO vibrational band origin with a combined standard uncertainty of 770 kHz (fractional uncertainty of 4 × 10).
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http://dx.doi.org/10.1016/j.jms.2018.07.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459610PMC
January 2018

Optical Measurement of Radiocarbon below Unity Fraction Modern by Linear Absorption Spectroscopy.

J Phys Chem Lett 2017 Sep 11;8(18):4550-4556. Epub 2017 Sep 11.

National Institute of Standards and Technology , 100 Bureau Drive, Gaithersburg, Maryland 20899, United States.

High-precision measurements of radiocarbon (C) near or below a fraction modern C of 1 (FC ≤ 1) are challenging and costly. An accurate, ultrasensitive linear absorption approach to detecting C would provide a simple and robust benchtop alternative to off-site accelerator mass spectrometry facilities. Here we report the quantitative measurement of C in gas-phase samples of CO with FC < 1 using cavity ring-down spectroscopy in the linear absorption regime. Repeated analysis of CO derived from the combustion of either biogenic or petrogenic sources revealed a robust ability to differentiate samples with FC < 1. With a combined uncertainty of C/C = 130 fmol/mol (FC = 0.11), initial performance of the calibration-free instrument is sufficient to investigate a variety of applications in radiocarbon measurement science including the study of biofuels and bioplastics, illicitly traded specimens, bomb dating, and atmospheric transport.
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http://dx.doi.org/10.1021/acs.jpclett.7b02105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5725230PMC
September 2017

Heterozygous mice reveal novel roles for the planar cell polarity pathway in adult lung homeostasis and repair.

Dis Model Mech 2017 04 24;10(4):409-423. Epub 2017 Feb 24.

Inflammation Repair and Development Section, National Heart and Lung Institute, Imperial College London, London SW7 2AZ, UK

Lung diseases impose a huge economic and health burden worldwide. A key aspect of several adult lung diseases, such as idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD), including emphysema, is aberrant tissue repair, which leads to an accumulation of damage and impaired respiratory function. Currently, there are few effective treatments available for these diseases and their incidence is rising. The planar cell polarity (PCP) pathway is critical for the embryonic development of many organs, including kidney and lung. We have previously shown that perturbation of the PCP pathway impairs tissue morphogenesis, which disrupts the number and shape of epithelial tubes formed within these organs during embryogenesis. However, very little is known about the role of the PCP pathway beyond birth, partly because of the perinatal lethality of many PCP mouse mutant lines. Here, we investigate heterozygous () mice, in which a single copy of the core PCP gene, , is disrupted. We show that these mice are viable but display severe airspace enlargement and impaired adult lung function. Underlying these defects, we find that lungs exhibit altered distribution of actin microfilaments and abnormal regulation of the actin-modifying protein cofilin. In addition, we show that lungs exhibit many of the hallmarks of tissue damage, including an altered macrophage population, abnormal elastin deposition and elevated levels of the elastin-modifying enzyme, , all of which are observed in emphysema. , disruption of impairs directed cell migration and reduces the rate of repair following scratch wounding of human alveolar epithelial cells. Moreover, using population data from a birth cohort of young adults, all aged 31, we found evidence of an interactive effect between and smoking on lung function. Finally, we show that PCP genes and are significantly downregulated in lung tissue from patients with emphysema. Our data reveal an important novel role for the PCP pathway in adult lung homeostasis and repair and shed new light on the genetic factors which may modify destructive lung diseases such as emphysema.
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http://dx.doi.org/10.1242/dmm.028175DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5399569PMC
April 2017

Diabetic Nephropathy: Perspective on Novel Molecular Mechanisms.

Trends Endocrinol Metab 2016 11 25;27(11):820-830. Epub 2016 Jul 25.

Developmental Biology and Cancer Programme, Institute of Child Health, University College London, London, WC1N 1EH, UK. Electronic address:

Diabetes mellitus (DM) is the major cause of end-stage renal disease (ESRD) globally, and novel treatments are urgently needed. Current therapeutic approaches for diabetic nephropathy (DN) are focussing on blood pressure control with inhibitors of the renin-angiotensin-aldosterone system, on glycaemic and lipid control, and life-style changes. In this review, we highlight new molecular insights aiding our understanding of the initiation and progression of DN, including glomerular insulin resistance, dysregulation of cellular substrate utilisation, podocyte-endothelial communication, and inhibition of tubular sodium coupled glucose reabsorption. We believe that these mechanisms offer new therapeutic targets that can be exploited to develop important renoprotective treatments for DN over the next decade.
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http://dx.doi.org/10.1016/j.tem.2016.07.002DOI Listing
November 2016

Planar cell polarity genes Celsr1 and Vangl2 are necessary for kidney growth, differentiation, and rostrocaudal patterning.

Kidney Int 2016 12 2;90(6):1274-1284. Epub 2016 Sep 2.

Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health, London, UK. Electronic address:

The mammalian kidney contains nephrons comprising glomeruli and tubules joined to ureteric bud-derived collecting ducts. It has a characteristic bean-like shape, with near-complete rostrocaudal symmetry around the hilum. Here we show that Celsr1, a planar cell polarity (PCP) gene implicated in neural tube morphogenesis, is required for ureteric tree growth in early development and later in gestation prevents tubule overgrowth. We also found an interaction between Celsr1 and Vangl2 (another PCP gene) in ureteric tree growth, most marked in the caudal compartment of the kidneys from compound heterozygous mutant mice with a stunted rump. Furthermore, these genes together are required for the maturation of glomeruli. Interestingly, we demonstrated patients with CELSR1 mutations and spina bifida can have significant renal malformations. Thus, PCP genes are important in mammalian kidney development and have an unexpected role in rostrocaudal patterning during organogenesis.
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http://dx.doi.org/10.1016/j.kint.2016.07.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126096PMC
December 2016

Loss of endogenous thymosin β accelerates glomerular disease.

Kidney Int 2016 11 26;90(5):1056-1070. Epub 2016 Aug 26.

Developmental Biology and Cancer Programme, UCL Institute of Child Health, London, United Kingdom. Electronic address:

Glomerular disease is characterized by morphologic changes in podocyte cells accompanied by inflammation and fibrosis. Thymosin β regulates cell morphology, inflammation, and fibrosis in several organs and administration of exogenous thymosin β improves animal models of unilateral ureteral obstruction and diabetic nephropathy. However, the role of endogenous thymosin β in the kidney is unknown. We demonstrate that thymosin β is expressed prominently in podocytes of developing and adult mouse glomeruli. Global loss of thymosin β did not affect healthy glomeruli, but accelerated the severity of immune-mediated nephrotoxic nephritis with worse renal function, periglomerular inflammation, and fibrosis. Lack of thymosin β in nephrotoxic nephritis led to the redistribution of podocytes from the glomerular tuft toward the Bowman capsule suggesting a role for thymosin β in the migration of these cells. Thymosin β knockdown in cultured podocytes also increased migration in a wound-healing assay, accompanied by F-actin rearrangement and increased RhoA activity. We propose that endogenous thymosin β is a modifier of glomerular injury, likely having a protective role acting as a brake to slow disease progression.
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http://dx.doi.org/10.1016/j.kint.2016.06.032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5073078PMC
November 2016

Aging-associated renal disease in mice is fructokinase dependent.

Am J Physiol Renal Physiol 2016 10 27;311(4):F722-F730. Epub 2016 Jul 27.

Division of Renal Diseases and Hypertension, University of Colorado, Aurora, Colorado; Division of Nephrology, Eastern Colorado Health Care System, Department of Veteran Affairs, Denver, Colorado.

Aging-associated kidney disease is usually considered a degenerative process associated with aging. Recently, it has been shown that animals can produce fructose endogenously, and that this can be a mechanism for causing kidney damage in diabetic nephropathy and in association with recurrent dehydration. We therefore hypothesized that low-level metabolism of endogenous fructose might play a role in aging-associated kidney disease. Wild-type and fructokinase knockout mice were fed a normal diet for 2 yr that had minimal (<5%) fructose content. At the end of 2 yr, wild-type mice showed elevations in systolic blood pressure, mild albuminuria, and glomerular changes with mesangial matrix expansion, variable mesangiolysis, and segmental thrombi. The renal injury was amplified by provision of high-salt diet for 3 wk, as noted by the presence of glomerular hypertrophy, mesangial matrix expansion, and alpha smooth muscle actin expression, and with segmental thrombi. Fructokinase knockout mice were protected from renal injury both at baseline and after high salt intake (3 wk) compared with wild-type mice. This was associated with higher levels of active (phosphorylated serine 1177) endothelial nitric oxide synthase in their kidneys. These studies suggest that aging-associated renal disease might be due to activation of specific metabolic pathways that could theoretically be targeted therapeutically, and raise the hypothesis that aging-associated renal injury may represent a disease process as opposed to normal age-related degeneration.
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http://dx.doi.org/10.1152/ajprenal.00306.2016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5142232PMC
October 2016

Coherent cavity-enhanced dual-comb spectroscopy.

Opt Express 2016 May;24(10):10424-34

Dual-comb spectroscopy allows for the rapid, multiplexed acquisition of high-resolution spectra without the need for moving parts or low-resolution dispersive optics. This method of broadband spectroscopy is most often accomplished via tight phase locking of two mode-locked lasers or via sophisticated signal processing algorithms, and therefore, long integration times of phase coherent signals are difficult to achieve. Here we demonstrate an alternative approach to dual-comb spectroscopy using two phase modulator combs originating from a single continuous-wave laser capable of > 2 hours of coherent real-time averaging. The dual combs were generated by driving the phase modulators with step-recovery diodes where each comb consisted of > 250 teeth with 203 MHz spacing and spanned > 50 GHz region in the near-infrared. The step-recovery diodes are passive devices that provide low-phase-noise harmonics for efficient coupling into an enhancement cavity at picowatt optical powers. With this approach, we demonstrate the sensitivity to simultaneously monitor ambient levels of CO2, CO, HDO, and H2O in a single spectral region at a maximum acquisition rate of 150 kHz. Robust, compact, low-cost and widely tunable dual-comb systems could enable a network of distributed multiplexed optical sensors.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4946650PMC
http://dx.doi.org/10.1364/OE.24.010424DOI Listing
May 2016

Precision Interferometric Measurements of Mirror Birefringence in High-Finesse Optical Resonators.

Phys Rev A (Coll Park) 2016 Jan 19;93(1). Epub 2016 Jan 19.

National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.

High-finesse optical resonators found in ultrasensitive laser spectrometers utilize supermirrors ideally consisting of isotropic high-reflectivity coatings. Strictly speaking, however, the optical coatings are often non-uniformly stressed during the deposition process and therefore do possess some small amount of birefringence. When physically mounted the cavity mirrors can be additionally stressed in such a way that large optical birefringence is induced. Here we report a direct measurement of optical birefringence in a two-mirror Fabry-Pérot cavity with = 99.99 % by observing TEM mode beating during cavity decays. Experiments were performed at a wavelength of 4.53 m, with precision limited by both quantum and technical noise sources. We report a splitting of = 618(1) Hz, significantly less than the intrinsic cavity linewidth of ≈ 3 kHz. With a cavity free spectral range of 96.9 MHz, the equivalent fractional change in mirror refractive index due to birefringence is therefore Δ/ = 6.38(1) × 10.
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http://dx.doi.org/10.1103/physreva.93.013833DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4832426PMC
January 2016