Type IV collagen of the glomerular basement membrane. Evidence that the chain specificity of network assembly is encoded by the noncollagenous NC1 domains

Choroidal and retinal thinning in chronic kidney disease independently associate with eGFR decline and are modifiable with treatment

In patients with chronic kidney disease (CKD), there is an unmet need for novel biomarkers that reliably track kidney injury, demonstrate treatment-response, and predict outcomes. Here, we investigate the potential of retinal optical coherence tomography (OCT) to achieve these ends in a series of prospective studies of patients with pre-dialysis CKD (including those with a kidney transplant), patients with kidney failure undergoing kidney transplantation, living kidney donors, and healthy volunteers. Compared to health, we observe similar retinal thinning and reduced macular volume in patients with CKD and in those with a kidney transplant. However, the choroidal thinning observed in CKD is not seen in patients with a kidney transplant whose choroids resemble those of healthy volunteers. In CKD, the degree of choroidal thinning relates to falling eGFR and extent of kidney scarring. Following kidney transplantation, choroidal thickness increases rapidly (~10%) and is maintained over 1-year, whereas gradual choroidal thinning is seen during the 12 months following kidney donation. In patients with CKD, retinal and choroidal thickness independently associate with eGFR decline over 2 years. These observations highlight the potential for retinal OCT to act as a non-invasive monitoring and prognostic biomarker of kidney injury.

Collagen IV of basement membranes: II. Emergence of collagen IVα345 enabled the assembly of a compact GBM as an ultrafilter in mammalian kidneys

The collagen IVα345 (Col-IVα345) scaffold, the major constituent of the glomerular basement membrane (GBM), is a critical component of the kidney glomerular filtration barrier. In Alport syndrome, affecting millions of people worldwide, over two thousand genetic variants occur in the COL4A3, COL4A4, and COL4A5 genes that encode the Col-IVα345 scaffold. Variants cause loss of scaffold, a suprastructure that tethers macromolecules, from the GBM or assembly of a defective scaffold, causing hematuria in nearly all cases, proteinuria, and often progressive kidney failure. How these variants cause proteinuria remains an enigma. In a companion paper, we found that the evolutionary emergence of the COL4A3, COL4A4, COL4A5, and COL4A6 genes coincided with kidney emergence in hagfish and shark and that the COL4A3 and COL4A4 were lost in amphibians. These findings opened an experimental window to gain insights into functionality of the Col-IVα345 scaffold. Here, using tissue staining, biochemical analysis and TEM, we characterized the scaffold chain arrangements and the morphology of the GBM of hagfish, shark, frog, and salamander. We found that α4 and α5 chains in shark GBM and α1 and α5 chains in amphibian GBM are spatially separated. Scaffolds are distinct from one another and from the mammalian Col-IVα345 scaffold, and the GBM morphologies are distinct. Our findings revealed that the evolutionary emergence of the Col-IVα345 scaffold enabled the genesis of a compact GBM that functions as an ultrafilter. Findings shed light on the conundrum, defined decades ago, whether the GBM or slit diaphragm is the primary filter.

The Phenotypic Spectrum of COL4A3 Heterozygotes

Introduction

The penetrance and phenotypic spectrum of autosomal dominant Alport Syndrome (ADAS), affecting 1 in 106, remains understudied.

Methods

Using data from 174,418 participants in the Geisinger MyCode/DiscovEHR study, an unselected health system-based cohort with whole exome sequencing, we identified 403 participants who were heterozygous for likely pathogenic COL4A3 variants. Phenotypic data was evaluated using International Classification of Diseases (ICD) codes, laboratory data, and chart review. To evaluate the phenotypic spectrum of genetically-determined ADAS, we matched COL4A3 heterozygotes 1:5 to nonheterozygotes using propensity scores by demographics, hypertension, diabetes, and nephrolithiasis.

Results

COL4A3 heterozygotes were at significantly increased risks of hematuria, decreased estimated glomerular filtration rate (eGFR), albuminuria, and kidney failure (P < 0.05 for all comparisons) but not bilateral sensorineural hearing loss (P = 0.9). Phenotypic severity was more severe for collagenous domain glycine missense variants than protein truncating variants (PTVs). For example, patients with Gly695Arg (n = 161) had markedly increased risk of dipstick hematuria (odds ratio [OR] 9.50; 95% confidence interval [CI]: 6.32, 14.28) and kidney failure (OR 7.02; 95% CI: 3.48, 14.16) whereas those with PTVs (n = 119) had moderately increased risks of dipstick hematuria (OR 1.64; 95% CI: 1.03, 2.59) and kidney failure (OR 3.44; 95% CI: 1.28, 9.22). Less than a third of patients had albuminuria screening completed, and fewer than 1 of 3 were taking inhibitors of the renin-angiotensin-aldosterone system.

Conclusion

This study demonstrates a wide spectrum of phenotypic severity in ADAS due to COL4A3 with phenotypic variability by genotype. Future studies are needed to evaluate the impact of earlier diagnosis, appropriate evaluation, and treatment of ADAS.

Effect of tissue fixation on the optical properties of structural components assessed by non-linear microscopy imaging

Fixation methods such as formalin are commonly used for the preservation of tissue with the aim of keeping their structure as close as possible to the native condition. However, fixatives chemically interact with tissue molecules, such as collagen in the extracellular matrix (ECM) or myosin, and may thus modify their structure. Taking advantage of the second- and third-harmonic generation (SHG and THG) emission capabilities of such components, we used nonlinear two-photon microscopy (NL2PM) to evaluate the effect that preservation methods, such as chemical fixatives, have on the nonlinear capabilities of protein components within mouse tissues. Our results show that depending on the preservation technique used, the nonlinear capabilities of collagen, lipid droplets and myosin microarchitecture are strongly affected. Parameters of collagen fibers, such as density and branch points, especially in collagen-sparse regions, e.g., in kidneys, were found to be altered upon formalin fixation. Moreover, cryo-freezing drastically reduced SHG signals from myosin. Our findings provide valuable information to select the best tissue fixation method for visualization and quantification of structural proteins, such as collagen and myosin by advanced NL2PM imaging techniques. This may advance the interpretation of the role these proteins play in disease.

Ocular manifestations in renal diseases

The eyes and kidneys are the targets for end-organ damage in multiple pathologies. Both these organs develop during the same embryonic stage around the fourth to sixth week of gestation, thus sharing a strong correlation between both eye and kidney diseases. Both the eyes and kidneys can be the target of the systemic disease process; however, the eyes can also be affected as a consequence of renal disease or its treatment. Risk factors such as diabetes, hypertension, and smoking are commonly shared between kidney and eye diseases. Ocular manifestations can be predictive of renal disease, and/or patients with renal disease are at higher risk for developing ocular manifestations. Various congenital anomalies of the eyes and kidneys can also present as an oculorenal syndrome. This article summarizes the ocular pathology, which can be seen in renal diseases.

The Phenotypic Spectrum of COL4A3 Heterozygotes

Most data on Alport Syndrome (AS) due to COL4A3 are limited to families with autosomal recessive AS or severe manifestations such as focal segmental glomerulosclerosis (FSGS). Using data from 174,418 participants in the Geisinger MyCode/DiscovEHR study, an unselected health system-based cohort with whole exome sequencing, we identified 403 participants (0.2%) who were heterozygous for likely pathogenic COL4A3 variants. Phenotypic data was evaluated using International Classification of Diseases (ICD) codes, laboratory data, and chart review. To evaluate the phenotypic spectrum of genetically-determined autosomal dominant AS, we matched COL4A3 heterozygotes 1:5 to non-heterozygotes using propensity scores by demographics, hypertension, diabetes, and nephrolithiasis. COL4A3 heterozygotes were at significantly increased risks of hematuria, decreased estimated glomerular filtration rate (eGFR), albuminuria, and end-stage kidney disease (ESKD) (p<0.05 for all comparisons) but not bilateral sensorineural hearing loss (p=0.9). Phenotypic severity tended to be more severe among patients with glycine missense variants located within the collagenous domain. For example, patients with Gly695Arg (n=161) had markedly increased risk of dipstick hematuria (OR 9.47, 95% CI: 6.30, 14.22) and ESKD diagnosis (OR 7.01, 95% CI: 3.48, 14.12) whereas those with PTVs (n=119) had moderately increased risks of dipstick hematuria (OR 1.63, 95% CI: 1.03, 2.58) and ESKD diagnosis (OR 3.43, 95% CI: 1.28, 9.19). Less than a third of patients had albuminuria screening completed, and fewer than 1/3 were taking inhibitors of the renin-angiotensin-aldosterone system (RAASi). Future studies are needed to evaluate the impact of earlier diagnosis, appropriate evaluation, and treatment of ADAS.

Identification of COL4A4 variants in Chinese patients with familial hematuria

Background: Benign familial hematuria and Alport syndrome are common causes of familial hematuria among children and young adults, which are attributable to variants in the collagen type IV alpha chain genes, COL4A3, COL4A4, or COL4A5. The study was conducted to identify the underlying genetic causes in patients with familial hematuria. Methods: Two unrelated Han-Chinese pedigrees with familial hematuria were recruited for this study. Whole exome sequencing was combined with in silico analysis to identify potential genetic variants, followed by variant confirmation by Sanger sequencing. Reverse transcription, PCR, and Sanger sequencing were performed to evaluate the effect of the detected splicing variant on mRNA splicing. Results: A novel heterozygous splicing c.595-1G>A variant and a known heterozygous c.1715G>C variant in the collagen type IV alpha 4 chain gene (COL4A4) were identified and confirmed in patients of pedigree 1 and pedigree 2, respectively. Complementary DNA analysis indicated this splicing variant could abolish the canonical splice acceptor site and cause a single nucleotide deletion of exon 10, which was predicted to produce a truncated protein. Conclusions: The two COL4A4 variants, c.595-1G>A variant and c.1715G>C (p.Gly572Ala) variant, were identified as the genetic etiologies of two families with familial hematuria, respectively. Our study broadened the variant spectrum of the COL4A4 gene and explained the possible pathogenesis, which will benefit clinical management and genetic counseling.

A novel nanoluciferase transgenic reporter measures proteinuria in zebrafish

The zebrafish is an important animal system for modeling human diseases. This includes kidney dysfunction as the embryonic kidney (pronephros) shares considerable molecular and morphological homology with the human nephron. A key clinical indicator of kidney disease is proteinuria, but a high-throughput readout of proteinuria in the zebrafish is currently lacking. To remedy this, we used the Tol2 transposon system to generate a transgenic zebrafish line that uses the fabp10a liver-specific promoter to over-express a nanoluciferase molecule fused with the D3 domain of Receptor-Associated Protein (a type of molecular chaperone) which we term NL-D3. Using a luminometer, we quantified proteinuria in NL-D3 zebrafish larvae by measuring the intensity of luminescence in the embryo medium. In the healthy state, NL-D3 is not excreted, but when embryos were treated with chemicals that affected either proximal tubular reabsorption (cisplatin, gentamicin) or glomerular filtration (angiotensin II, Hanks Balanced Salt Solution, Bovine Serum Albumin), NL-D3 is detected in fish medium. Similarly, depletion of several gene products associated with kidney disease (nphs1, nphs2, lrp2a, ocrl, col4a3, and col4a4) also induced NL-D3 proteinuria. Treating col4a4 depleted zebrafish larvae (a model of Alport syndrome) with captopril reduced proteinuria in this system. Thus, our findings validate the use of the NL-D3 transgenic zebrafish as a robust and quantifiable proteinuria reporter. Hence, given the feasibility of high-throughput assays in zebrafish, this novel reporter will permit screening for drugs that ameliorate proteinuria, thereby prioritizing candidates for further translational studies.

A novel nanoluciferase transgenic reporter measures proteinuria in zebrafish

The zebrafish is an important animal system for modeling human diseases. This includes kidney dysfunction as the embryonic kidney (pronephros) shares considerable molecular and morphological homology with the human nephron. A key clinical indicator of kidney disease is proteinuria, but a high-throughput readout of proteinuria in the zebrafish is currently lacking. To remedy this, we used the Tol2 transposon system to generate a transgenic zebrafish line that uses the fabp10a liver-specific promoter to over-express a nanoluciferase molecule fused with the D3 domain of Receptor-Associated Protein (a type of molecular chaperone) which we term NL-D3. Using a luminometer, we quantified proteinuria in NL-D3 zebrafish larvae by measuring the intensity of luminescence in the embryo medium. In the healthy state, NL-D3 is not excreted, but when embryos were treated with chemicals that affected either proximal tubular reabsorption (cisplatin, gentamicin) or glomerular filtration (angiotensin II, Hanks Balanced Salt Solution, Bovine Serum Albumin), NL-D3 is detected in fish medium. Similarly, depletion of several gene products associated with kidney disease (nphs1, nphs2, lrp2a, ocrl, col4a3, and col4a4) also induced NL-D3 proteinuria. Treating col4a4 depleted zebrafish larvae (a model of Alport syndrome) with captopril reduced proteinuria in this system. Thus, our findings validate the use of the NL-D3 transgenic zebrafish as a robust and quantifiable proteinuria reporter. Hence, given the feasibility of high-throughput assays in zebrafish, this novel reporter will permit screening for drugs that ameliorate proteinuria, thereby prioritizing candidates for further translational studies.

A Simple Review of Small Vessel Disease Manifestation in the Brain, Retina, and Kidneys

Small blood vessels express specific phenotypical and functional characteristics throughout the body. Alterations in the microcirculation contribute to many correlated physiological and pathological events in related organs. Factors such as comorbidities and genetics contribute to the complexity of this topic. Small vessel disease primarily affects end organs that receive significant cardiac output, such as the brain, kidney, and retina. Despite the differences in location, concurrent changes are seen in the micro-vasculature of the brain, retina, and kidneys under pathological conditions due to their common histological, functional, and embryological characteristics. While the cardiovascular basis of pathology in association with the brain, retina, or kidneys has been well documented, this is a simple review that uniquely considers the relationship between all three organs and highlights the prevalence of coexisting end organ injuries in an attempt to elucidate connections between the brain, retina, and kidneys, which has the potential to transform diagnostic and therapeutic approaches.

Prospective collagen IVα345 therapies for Alport syndrome

PURPOSE OF REVIEW

In Alport syndrome, over 1,700 genetic variants in the COL4A3, COL4A4, and COL4A5 genes cause the absence or malfunctioning of the collagen IVα345 scaffold - an essential component of the glomerular basement membrane (GBM). Therapies are limited to treatment with Angiotensin-Converting enzyme (ACE) inhibitors to slow progression of the disease. Here, we review recent progress in therapy development to replace the scaffold or restore its function.

RECENT FINDINGS

Multiple approaches emerged recently for development of therapies that target different stages of production and assembly of the collagen IVα345 scaffold in the GBM. These approaches are based on (1) recent advances in technologies allowing to decipher pathogenic mechanisms that underlie scaffold assembly and dysfunction, (2) development of DNA editing tools for gene therapy, (3) RNA splicing interference, and (4) control of mRNA translation.

SUMMARY

There is a growing confidence that these approaches will ultimately provide cure for Alport patients. The development of therapy will be accelerated by studies that provide a deeper understanding of mechanisms that underlie folding, assembly, and function of the collagen IVα345 scaffold.

Corneal fibroblast collagen type IV negative feedback modulation of TGF beta: A fibrosis modulating system likely active in other organs

Collagen type IV (COL IV) is a major component of basement membranes (BM) in all organs. It serves functions related to BM organization and modulates the passage of growth factors from one tissue compartment to another. COL IV binds transforming growth factor (TGF) beta-1 and TGF beta-2 and, therefore, is a major modulator of TGF beta pro-fibrotic functions. After fibrotic corneal injury, TGF beta enters into the stroma from the tears, epithelium, endothelium and/or aqueous humor and markedly upregulates COL IV production in corneal fibroblasts in the adjacent stroma far removed from BMs. It is hypothesized this non-BM stromal COL IV binds TGF beta-1 (and likely TGF beta-2) in competition with the binding of the growth factors to TGF beta cognate receptors and serves as a negative feedback regulatory pathway to mitigate the effects of TGF beta on stromal cells, including reducing the developmental transition of corneal fibroblasts and fibrocytes into myofibroblasts. Losartan, a known TGF beta signaling inhibitor, when applied topically to the cornea after fibrotic injury, alters this COL IV-TGF beta pathway by down-regulating COL IV production by corneal fibroblasts. Non-BM COL IV produced in response to injuries in other organs, including the lung, skin, liver, kidney, and gut, may participate in similar COL IV-TGF beta pathways and have an important role in controlling TGF beta pro-fibrotic effects in these organs.

Identification of Four Novel COL4A5 Variants and Detection of Splicing Abnormalities in Three Chinese X-Linked Alport Syndrome Families

Chronic renal disease associated with X-linked Alport syndrome (XLAS) is relatively rare. However, due to the lack of specificity in the pathologic and clinical manifestations of the disease, it is easy to be misdiagnosed. In this study, we included three Chinese families with XLAS and used targeted NGS to find gene variants. In family X1, the 36-year-old male proband had hematuria, massive proteinuria, sensorineural deafness and ESRD at 33. In silico prediction showed the novel c.1424-4C > G variant reduced the score of the normal 3’ splice site from 0.47 to 0.00 (according to BDGP). Transcriptional analysis from his peripheral blood cells indicated that it caused the insertion of an amino acid [p.(Lys474_Gly475insVal)]. In family X2, the proband was a 32-year-old male, who had hematuria, proteinuria, hypertension, hearing loss and progressed into ESRD at 30 years. He carried a novel missense variant c.2777G > T p.(Gly926Val). In family X3, the proband, a 16-year-old male, had hematuria, massive proteinuria, sensorineural deafness and ESRD; the results of renal pathological findings were consistent with AS. He carried a novel variant c.4529-2A > T, so did his mother with ESRD and probable XLAS. Bioinformatic analysis with BDGP showed that it abolished the acceptor site from 0.83 to 0.00. RT-PCR analysis from his kidney tissue indicated that it caused exon 50 skipping and exon 50 skipping along with inserting a cryptic exon derived from intron 49 p.[Gly1510Aspfs*11, Gly1510Alafs*35]. Another novel missense variant c.1552G > A p.(Gly518Arg) was identified in his mother and his aunt. No skewed X-chromosome inactivation was involved in these two female patients. In conclusion, four novel variants in COL4A5 were identified and transcriptional analysis is essential to investigate the pathogenicity of intronic variants. Thus we found a rare event in a female patient with XLAS caused by two COL4A5 variants in trans.

Molecular and Cellular Mechanisms Underlying the Initiation and Progression of Alport Glomerular Pathology

Alport syndrome results from a myriad of variants in the COL4A3, COL4A4, or COL4A5 genes that encode type IV (basement membrane) collagens. Unlike type IV collagen α1(IV)₂α2(IV)₁ heterotrimers, which are ubiquitous in basement membranes, α3/α4/α5 have a limited tissue distribution. The absence of these basement membrane networks causes pathologies in some, but not all these tissues. Primarily the kidney glomerulus, the stria vascularis of the inner ear, the lens, and the retina as well as a rare link with aortic aneurisms. Defects in the glomerular basement membranes results in delayed onset and progressive focal segmental glomerulosclerosis ultimately requiring the patient to undergo dialysis and if accessible, kidney transplant. The lifespan of patients with Alport syndrome is ultimately significantly shortened. This review addresses the consequences of the altered glomerular basement membrane composition in Alport syndrome with specific emphasis on the mechanisms underlying initiation and progression of glomerular pathology.

Assessment of renal fibrosis and anti-fibrotic agents using a novel diagnostic and stain-free second-harmonic generation platform

Current histological measurement techniques for interstitial collagen, the basis of interstitial fibrosis, are semi-quantitative at best and only provide a ratio of collagen levels within tissues. The Genesis200 imaging system and supplemental image analysis software, FibroIndex from HistoIndex, is a novel, automated platform that uses second-harmonic generation (SHG) for imaging and characterization of interstitial collagen deposition and additional characteristics, in the absence of any staining. However, its ability to quantify renal fibrosis requires investigation. This study compared SHG imaging of renal fibrosis in mice with unilateral ureteric obstruction (UUO), to that of Masson's trichrome staining (MTS) and immunohistochemistry (IHC) of collagen I. Additionally, the platform generated data on collagen morphology and distribution patterns. While all three methods determined that UUO-injured mice underwent significantly increased renal fibrosis after 7 days, the HistoIndex platform additionally determined that UUO-injured mice had a significantly increased collagen-to-tissue cross reticulation ratio (all P < .001 vs sham group). Furthermore, in UUO-injured mice treated with the relaxin family peptide receptor-1 agonists, relaxin (0.5 mg/kg/day) or B7-33 (0.25 mg/kg/day), or angiotensin converting enzyme-inhibitor, perindopril (1 mg/kg/day) over the 7-day period, only the HistoIndex platform determined that the drug-induced prevention of renal fibrosis correlated with significantly reduced collagen fiber thickness and collagen-to-tissue cross reticulation ratio, but increased collagen fiber counts. Relaxin or B7-33 treatment also increased renal matrix metalloproteinase-2 and reduced tissue inhibitor of metalloproteinase-1 levels (all P < .01 vs UUO alone). This study demonstrated the diagnostic value of the HistoIndex platform over currently used staining techniques.

Relapse of pathological angiogenesis: functional role of the basement membrane and potential treatment strategies

Blinding eye diseases such as corneal neovascularization, proliferative diabetic retinopathy, and age-related macular degeneration are driven by pathological angiogenesis. In cancer, angiogenesis is key for tumor growth and metastasis. Current antiangiogenic treatments applied clinically interfere with the VEGF signaling pathway-the main angiogenic pathway-to inhibit angiogenesis. These treatments are, however, only partially effective in regressing new pathologic vessels, and the disease relapses following cessation of treatment. Moreover, the relapse of pathological angiogenesis can be rapid, aggressive and more difficult to treat than angiogenesis in the initial phase. The manner in which relapse occurs is poorly understood; however, recent studies have begun to shed light on the mechanisms underlying the revascularization process. Hypotheses have been generated to explain the rapid angiogenic relapse and increased resistance of relapsed disease to treatment. In this context, the present review summarizes knowledge of the various mechanisms of disease relapse gained from different experimental models of pathological angiogenesis. In addition, the basement membrane-a remnant of regressed vessels-is examined in detail to discuss its potential role in disease relapse. Finally, approaches for gaining a better understanding of the relapse process are discussed, including prospects for the management of relapse in the context of disease.

The eye, the kidney, and cardiovascular disease: old concepts, better tools, and new horizons

Chronic kidney disease (CKD) is common, with hypertension and diabetes mellitus acting as major risk factors for its development. Cardiovascular disease is the leading cause of death worldwide and the most frequent end point of CKD. There is an urgent need for more precise methods to identify patients at risk of CKD and cardiovascular disease. Alterations in microvascular structure and function contribute to the development of hypertension, diabetes, CKD, and their associated cardiovascular disease. Homology between the eye and the kidney suggests that noninvasive imaging of the retinal vessels can detect these microvascular alterations to improve targeting of at-risk patients. Retinal vessel-derived metrics predict incident hypertension, diabetes, CKD, and cardiovascular disease and add to the current renal and cardiovascular risk stratification tools. The advent of optical coherence tomography (OCT) has transformed retinal imaging by capturing the chorioretinal microcirculation and its dependent tissue with near-histological resolution. In hypertension, diabetes, and CKD, OCT has revealed vessel remodeling and chorioretinal thinning. Clinical and preclinical OCT has linked retinal microvascular pathology to circulating and histological markers of injury in the kidney. The advent of OCT angiography allows contrast-free visualization of intraretinal capillary networks to potentially detect early incipient microvascular disease. Combining OCT's deep imaging with the analytical power of deep learning represents the next frontier in defining what the eye can reveal about the kidney and broader cardiovascular health.

CG200745, a Novel HDAC Inhibitor, Attenuates Kidney Fibrosis in a Murine Model of Alport Syndrome

Histone deacetylases have been a target of therapy for organ fibrosis. Here, we report the protective effect of CG200745 (CG), a novel histone deacetylase inhibitor, on tubulointerstitial fibrosis in Col4a3^-/- mice, a murine model of Alport syndrome. Morphological analyses revealed CG treatment markedly alleviated kidney fibrosis in Col4a3^-/- mice at the age of 7 weeks. CG prevented the activation of transforming growth factor β (TGFβ) and its downstream SMAD signaling in the kidney of Col4a3^-/- mice. As critical upstream regulators of TGFβ signaling, immunoblotting of whole kidney lysate of Col4a3^-/- mice reveled that intra-renal renin-angiotensin system (RAS) was activated with concurrent upregulation of inflammation and apoptosis, which were effectively suppressed by CG treatment. CG suppressed both activation of RAS and up-regulation of TGFβ signals in angiotensin II-stimulated HK-2 cells, a human kidney proximal tubular epithelial cell line. CG inhibited activation of TGFβ-driven signals and fibrosis in NRK-49F cells, a rat kidney fibroblast cell line, under angiotensin II-rich conditions. Collectively, CG was found to be effective both in proximal tubular epithelial cells by inhibiting local RAS and TGFβ signaling activation, as well as in fibroblasts by blocking their transition to myofibroblasts, attenuating renal fibrosis in a murine model of Alport syndrome.

Protein misfolding in endoplasmic reticulum stress with applications to renal diseases

Protein misfolding may be the result of a variety of different processes that disrupt the ability of a protein to form a thermodynamically stable tertiary structure that allows it to perform its proper function. In this chapter, we explore the nature of a protein's form that allows it to have a stable tertiary structure, and examine specific mutation that are known to occur in the coding regions of DNA that disrupt a protein's ability to be folded into a thermodynamically stable tertiary structure. We examine the consequences of these protein misfoldings in terms of the endoplasmic reticulum stress response and resulting unfolded protein response. These conditions are specifically related to renal diseases. Further, we explore novel therapeutics, pharmacological chaperones, that are being developed to alleviate the disease burden associated with protein misfolding caused by mutations. These interventions aim to stabilize protein folding intermediates and allow proper folding to occur as well as prevent protein aggregation and the resulting pathophysiological consequences.

Collagen IV Exploits a Cl- Step Gradient for Scaffold Assembly

Collagen molecules are crucial extracellular players in animal tissue development and in functions ranging from ultrafiltration to organism locomotion. Among the 28 types of collagen found in human, type IV collagen stands out as a primordial type found in all species of the animal kingdom. Collagen IV forms smart scaffolds for basement membranes, sheet-like acellular structures that isolate, coordinate, and direct cells during morphogenesis. Collagen IV is also involved in multiple functions in developed tissues. As part of the basement membrane, collagen IV scaffolds provide mechanical strength, spatially tether extracellular macromolecules and directly signal to cells via receptor binding sites. Proper assembly and structure of the scaffolds are critical for development and function of multiple types of basement membranes. Within last 5 years it was established that Cl^- concentration is a key factor for initiating collagen IV scaffold assembly. The biological role of Cl^- in multiple physiological processes and detailed mechanisms for its signaling and structural impacts are well established. Cl^- gradients are generated across the plasma and intracellular organelle membranes. As collagen IV molecules are secreted outside the cell, they experience a switch from low to high Cl^- concentration. This transition works as a trigger for collagen IV scaffold assembly. Within the scaffold, collagen IV remains to be a Cl^- sensor as its structural integrity continues to depend on Cl^- concentration. Here, we review recent findings and set future directions for studies on the role of Cl^- in type IV collagen assembly, function, and disease.

Complexity of type IV collagens: from network assembly to function

Collagens form complex networks in the extracellular space that provide structural support and signaling cues to cells. Network-forming type IV collagens are the key structural components of basement membranes. In this review, we discuss how the complexity of type IV collagen networks is established, focusing on collagen α chain selection in type IV collagen protomer and network formation; covalent crosslinking in type IV collagen network stabilization; and the differences between solid-state type IV collagen in the extracellular matrix and soluble type IV collagen fragments. We further discuss how complex type IV collagen networks exert their physiological and pathological functions through cell surface integrin and nonintegrin receptors.

The Non-Fibrillar Side of Fibrosis: Contribution of the Basement Membrane, Proteoglycans, and Glycoproteins to Myocardial Fibrosis

The extracellular matrix (ECM) provides structural support and a microenvironmentfor soluble extracellular molecules. ECM is comprised of numerous proteins which can be broadly classified as fibrillar (collagen types I and III) and non-fibrillar (basement membrane, proteoglycans, and glycoproteins). The basement membrane provides an interface between the cardiomyocytes and the fibrillar ECM, while proteoglycans sequester soluble growth factors and cytokines. Myocardial fibrosis was originally only linked to accumulation of fibrillar collagens, but is now recognized as the expansion of the ECM including the non-fibrillar ECM proteins. Myocardial fibrosis can be reparative to replace the lost myocardium (e.g., ischemic injury or myocardial infarction), or can be reactive resulting from pathological activity of fibroblasts (e.g., dilated or hypertrophic cardiomyopathy). Contribution of fibrillar collagens to fibrosis is well studied, but the role of the non-fibrillar ECM proteins has remained less explored. In this article, we provide an overview of the contribution of the non-fibrillar components of the extracellular space of the heart to highlight the potential significance of these molecules in fibrosis, with direct evidence for some, although not all of these molecules in their direct contribution to fibrosis.

Olmesartan Attenuates Kidney Fibrosis in a Murine Model of Alport Syndrome by Suppressing Tubular Expression of TGFβ

Despite the wide use of angiotensin II receptor blockers in the treatment of Alport syndrome (AS), the mechanism as to how angiotensin II receptor blockers prevent interstitial fibrosis remains unclear. Here, we report that treatment of olmesartan effectively targets the feedback loop between the renin–angiotensin system (RAS) and transforming growth factor β (TGFβ) signals in tubular epithelial cells and preserves renal angiotensin-converting enzyme 2 (ACE2) expression in the kidney of Col4a3^–/– mice, a murine model of experimental AS. Morphology analyses revealed amelioration of kidney fibrosis in Col4a3^–/– mice by olmesartan treatment. Upregulation of TGFβ and activation of its downstream in Col4a3^–/– mice were attenuated by olmesartan in Col4a3^–/– mice. Intriguingly, TGFβ expression was preferentially upregulated in damaged tubular epithelial cells in Col4a3^–/– mice. Concurrent upregulation of TNFα-converting enzyme and downregulation of ACE2 suggested RAS activation in Col4a3^–/– mice, which was prevented by olmesartan. Mechanistically, olmesartan suppressed TGFβ-induced RAS activation in tubular epithelial cells in vitro. Collectively, we concluded that olmesartan effectively suppresses the progression of tubulointerstitial fibrosis in AS by interrupting RAS-TGFβ feedback loop to counterbalance intrarenal RAS activation.

A chloride ring is an ancient evolutionary innovation mediating the assembly of the collagen IV scaffold of basement membranes

Collagen IV scaffold is a principal component of the basement membrane (BM), a specialized extracellular matrix that is essential for animal multicellularity and tissue evolution. Scaffold assembly begins with the trimerization of α-chains into protomers inside the cell, which then are secreted and undergo oligomerization outside the cell. For the ubiquitous scaffold composed of α1- and α2-chains, both intracellular and extracellular stages are mediated by the noncollagenous domain (NC1). The association of protomers is chloride-dependent, whereby chloride ions induce interactions of the protomers' trimeric NC1 domains leading to NC1 hexamer formation. Here, we investigated the mechanisms, kinetics, and functionality of the chloride ion-mediated protomer assembly by using a single-chain technology to produce a stable NC1 trimer comprising α1, α2, and α1 NC1 monomers. We observed that in the presence of chloride, the single-chain NC1-trimer self-assembles into a hexamer, for which the crystal structure was determined. We discovered that a chloride ring, comprising 12 ions, induces the assembly of and stabilizes the NC1 hexamer. Furthermore, we found that the chloride ring is evolutionarily conserved across all animals, first appearing in cnidarians. These findings reveal a fundamental role for the chloride ring in the assembly of collagen IV scaffolds of BMs, a critical event enabling tissue evolution and development. Moreover, the single-chain technology is foundational for generating trimeric NC1 domains of other α-chain compositions to investigate the α121, α345, and α565 collagen IV scaffolds and to develop therapies for managing Alport syndrome, Goodpasture's disease, and cancerous tumor growth.

Shining a Light on Alport Syndrome

In this issue of Cell Chemical Biology, Omachi et al. (2018) present a split Nanoluciferase system to identify successful protein trimerization in Alport syndrome. This elegant proof of concept suggests opportunities for drug screening for Alport syndrome and may be transferable to the study of other diseases affecting protein-protein interactions.

Structures of collagen IV globular domains: insight into associated pathologies, folding and network assembly

Basement membranes are extracellular structures of epithelia and endothelia that have collagen IV scaffolds of triple α-chain helical protomers that associate end-to-end, forming networks. The molecular mechanisms by which the noncollagenous C-terminal domains of α-chains direct the selection and assembly of the α1α2α1 and α3α4α5 hetero-oligomers found in vivo remain obscure. Autoantibodies against the noncollagenous domains of the α3α4α5 hexamer or mutations therein cause Goodpasture's or Alport's syndromes, respectively. To gain further insight into oligomer-assembly mechanisms as well as into Goodpasture's and Alport's syndromes, crystal structures of non-collagenous domains produced by recombinant methods were determined. The spontaneous formation of canonical homohexamers (dimers of trimers) of these domains of the α1, α3 and α5 chains was shown and the components of the Goodpasture's disease epitopes were viewed. Crystal structures of the α2 and α4 non-collagenous domains generated by recombinant methods were also determined. These domains spontaneously form homo-oligomers that deviate from the canonical architectures since they have a higher number of subunits (dimers of tetramers and of hexamers, respectively). Six flexible structural motifs largely explain the architectural variations. These findings provide insight into noncollagenous domain folding, while supporting the in vivo operation of extrinsic mechanisms for restricting the self-assembly of noncollagenous domains. Intriguingly, Alport's syndrome missense mutations concentrate within the core that nucleates the folding of the noncollagenous domain, suggesting that this syndrome, when owing to missense changes, is a folding disorder that is potentially amenable to pharmacochaperone therapy.

Alternative Pathway Is Essential for Glomerular Complement Activation and Proteinuria in a Mouse Model of Membranous Nephropathy

Membranous nephropathy is an immune kidney disease caused by IgG antibodies that form glomerular subepithelial immune complexes. Proteinuria is mediated by complement activation, as a result of podocyte injury by C5b-9, but the role of specific complement pathways is not known. Autoantibodies-mediating primary membranous nephropathy are predominantly of IgG4 subclass, which cannot activate the classical pathway. Histologic evidence from kidney biopsies suggests that the lectin and the alternative pathways may be activated in membranous nephropathy, but the pathogenic relevance of these pathways remains unclear. In this study, we evaluated the role of the alternative pathway in a mouse model of membranous nephropathy. After inducing the formation of subepithelial immune complexes, we found similar glomerular IgG deposition in wild-type mice and in factor B-null mice, which lack a functional alternative pathway. Unlike wild-type mice, mice lacking factor B did not develop albuminuria nor exhibit glomerular deposition of C3c and C5b-9. Albuminuria was also reduced but not completely abolished in C5-deficient mice. Our results provide the first direct evidence that the alternative pathway is necessary for pathogenic complement activation by glomerular subepithelial immune complexes and is, therefore, a key mediator of proteinuria in experimental membranous nephropathy. This knowledge is important for the rational design of new therapies for membranous nephropathy.

FPS-ZM1 and valsartan combination protects better against glomerular filtration barrier damage in streptozotocin-induced diabetic rats

Despite the effectiveness of renin-angiotensin blockade in retarding diabetic nephropathy progression, a considerable number of patients still develop end-stage renal disease. The present investigation aims to evaluate the protective potential of FPS-ZM1, a selective inhibitor of receptor for advanced glycation end products (RAGE), alone and in combination with valsartan, an angiotensin receptor blocker, against glomerular injury parameters in streptozotocin-induced diabetic rats. FPS-ZM1 at 1 mg/kg (i.p.), valsartan at 100 mg/kg (p.o.), and their combination were administered for 4 weeks, starting 2 months after diabetes induction in rats. Tests for kidney function, glomerular filtration barrier, and podocyte slit diaphragm integrities were performed. Combined FPS-ZM1/valsartan attenuated diabetes-induced elevations in renal levels of RAGE and phosphorylated NF-κB p65 subunit. It ameliorated glomerular injury due to diabetes by increasing glomerular nephrin and synaptopodin expressions, mitigating renal integrin-linked kinase (ILK) levels, and lowering urinary albumin, collagen type IV, and podocin excretions. FPS-ZM1 also improved renal function as demonstrated by decreasing levels of serum cystatin C. Additionally, the combination also alleviated indices of renal inflammation as revealed by decreased renal monocyte chemoattractant protein 1 (MCP-1) and chemokine (C-X-C motif) ligand 12 (CXCL12) expressions, F4/80-positive macrophages, glomerular TUNEL-positive cells, and urinary alpha-1-acid glycoprotein (AGP) levels. These findings underline the benefits of FPS-ZM1 added to valsartan in alleviating renal glomerular injury evoked by diabetes in streptozotocin rats and suggest FPS-ZM1 as a new potential adjunct to the conventional renin-angiotensin blockade.

Dunnione protects against experimental cisplatin-induced nephrotoxicity by modulating NQO1 and NAD+ levels

Despite being an efficacious anticancer agent, the clinical utility of cisplatin is hindered by its cardinal side effects. This investigation aimed to appraise potential protective impact of dunnione, a natural naphthoquinone pigment with established NQO1 stimulatory effects, on cisplatin nephrotoxicity of rats. Dunnione was administered orally at 10 and 20 mg/kg doses for 4 d and a single injection of cisplatin was delivered at the second day. Renal histopathology, inflammatory/oxidative stress/apoptotic markers, kidney function, and urinary markers of renal injury were assessed. Dunnione repressed cisplatin-induced inflammation in the kidneys as indicated by decreased TNF-α/IL-1β levels, and reduced nuclear phosphorylated NF-κB p65. This agent also obviated cisplatin-invoked oxidative stress as elucidated by decreased MDA/GSH levels and increased SOD/CAT activities. Dunnione, furthermore, improved renal histological deteriorations as well as caspase-3 activities and terminal deoxynucleotidyl transferase (TUNEL) positive cells, the indicators of apoptosis. Moreover, it up-regulated nuclear Nrf2 and cytosolic haeme-oxygenase-1 (HO-1) and NQO1 levels; meanwhile, promoted NAD⁺/NADH ratios followed by enhancing the activities of Sirt1 and PARP1; and further attenuated nuclear acetylated NF-κB p65. Dunnione additionally declined cisplatin-evoked retrogression in renal function and upraise in urinary markers of glomerular and tubular injury as demonstrated by decreased serum urea and creatinine with simultaneous reductions in urinary excretions of collagen type IV, podocin, cystatin C, and retinol-binding protein (RBP). Altogether, these findings offer dunnione as a potential protective agent against cisplatin-induced nephrotoxicity in rats.

Goodpasture's autoimmune disease - A collagen IV disorder

Goodpasture's (GP) disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung eliciting rapidly progressive glomerulonephritis and pulmonary hemorrhage. The principal autoantigen is the α345 network of collagen IV, which expression is restricted to target tissues. Recent discoveries include a key role of chloride and bromide for network assembly, a novel posttranslational modification of the antigen, a sulfilimine bond that crosslinks the antigen, and the mechanistic role of HLA in genetic susceptibility and resistance to GP disease. These advances provide further insights into molecular mechanisms of initiation and progression of GP disease and serve as a basis for developing of novel diagnostic tools and therapies for treatment of Goodpasture's disease.

From supramolecular polymers to multi-component biomaterials

The most striking and general property of the biological fibrous architectures in the extracellular matrix (ECM) is the strong and directional interaction between biologically active protein subunits. These fibers display rich dynamic behavior without losing their architectural integrity. The complexity of the ECM taking care of many essential properties has inspired synthetic chemists to mimic these properties in artificial one-dimensional fibrous structures with the aim to arrive at multi-component biomaterials. Due to the dynamic character required for interaction with natural tissue, supramolecular biomaterials are promising candidates for regenerative medicine. Depending on the application area, and thereby the design criteria of these multi-component fibrous biomaterials, they are used as elastomeric materials or hydrogel systems. Elastomeric materials are designed to have load bearing properties whereas hydrogels are proposed to support in vitro cell culture. Although the chemical structures and systems designed and studied today are rather simple compared to the complexity of the ECM, the first examples of these functional supramolecular biomaterials reaching the clinic have been reported. The basic concept of many of these supramolecular biomaterials is based on their ability to adapt to cell behavior as a result of dynamic non-covalent interactions. In this review, we show the translation of one-dimensional supramolecular polymers into multi-component functional biomaterials for regenerative medicine applications.

A Split-Luciferase-Based Trimer Formation Assay as a High-throughput Screening Platform for Therapeutics in Alport Syndrome

Alport syndrome is a hereditary glomerular disease caused by mutation in type IV collagen α3-α5 chains (α3-α5(IV)), which disrupts trimerization, leading to glomerular basement membrane degeneration. Correcting the trimerization of α3/α4/α5 chain is a feasible therapeutic approach, but is hindered by lack of information on the regulation of intracellular α(IV) chain and the absence of high-throughput screening (HTS) platforms to assess α345(IV) trimer formation. Here, we developed sets of split NanoLuc-fusion α345(IV) proteins to monitor α345(IV) trimerization of wild-type and clinically associated mutant α5(IV). The α345(IV) trimer assay, which satisfied the acceptance criteria for HTS, enabled the characterization of intracellular- and secretion-dependent defects of mutant α5(IV). Small interfering RNA-based and chemical screening targeting the ER identified several chemical chaperones that have potential to promote α345(IV) trimer formation. This split luciferase-based trimer formation assay is a functional HTS platform that realizes the feasibility of targeting α345(IV) trimers to treat Alport syndrome.

Diacerein alleviates kidney injury through attenuating inflammation and oxidative stress in obese insulin-resistant rats

A link between inflammation with obesity and metabolic syndrome has been found in patients with chronic kidney disease (CKD). Diacerein is an anthraquinone used to treat osteoarthritis that exerts anti-inflammatory action by inhibiting the synthesis and activity of proinflammatory cytokines. This study aimed to investigate the protective effect of diacerein on renal function and renal organic anion transporter 3 (Oat3) function in obese insulin-resistant condition. Obese insulin-resistant rats were induced by feeding a high-fat diet in male Wistar rats for 16 weeks. Diacerein or metformin (positive control) (30mg/kg/day) was administered orally for 4 weeks after insulin resistance had been confirmed. Obese insulin-resistant rats showed an impaired renal function as indicated by the increased serum creatinine and microalbuminuria along with the decreased renal Oat3 function and expression. Importantly, diacerein treatment not only improved insulin resistance but also restored renal function. The decreased renal malondialdehyde level, expressions of PKCα, angiotensin 1 receptor (AT1R), Nrf2, and HO-1, and increased expression of SOD2 were observed in diacerein treatment group, indicating the attenuation of renal oxidative stress condition. Moreover, renal inflammation and renal damage were also alleviated in diacerein-treated rats. Our results demonstrated for the first time that diacerein was effective to improve renal function and renal Oat3 function in obese insulin-resistance condition mediated by suppressing renal oxidative stress and inflammation. These findings suggest that anti-inflammatory agents can be used therapeutically to improve metabolic disorder and prevent organ dysfunctions in pre-diabetic condition.

Comparison of in vivo targeting ability between cRGD and collagen-targeting peptide conjugated nano-carriers for atherosclerosis

Atherosclerosis plaque is a major cause of cardiovascular diseases across the globe and a silent killer. There are no physical symptoms of the disease in its early stage and current diagnostic techniques cannot detect the small plaques effectively or safely. Plaques formed in blood vessels can cause serious clinical problems such as impaired blood flow or sudden death, regardless of their size. Thus, detecting early stage of plaques is especially more important to effectively reduce the risk of atherosclerosis. Nanoparticle based delivery systems are recognized as a promising option to fight against this disease, and various targeting ligands are typically used to improve their efficiency. So, the choice of appropriate targeting ligand is a crucial factor for optimal targeting efficiency. cRGD peptide and collagen IV targeting peptide, which binds with the α_vβ₃ integrin overexpressed in the neovasculature of the plaque and collagen type IV present in the plaque, respectively, are frequently used for the targeting of nanoparticles. However, at present no study has directly compared these two peptides. Therefore, in this study, we have prepared cRGD or collagen IV targeting (Col IV-tg-) peptide conjugated and iron oxide nanoparticle (IONP) loaded Pluronic based nano-carriers for systemic comparison of their targeting ability towards in vivo atherosclerotic plaque in Apolipoprotein E deficient (Apo E^-/-) mouse model. Nano-carriers with similar size, surface charge, and IONP loading content but with different targeting ligands were analyzed through in vitro and in vivo experiments. Near infrared fluorescence imaging and magnetic resonance imaging techniques as well as Prussian blue staining were used to compare the accumulation of different ligand conjugated nano-caariers in the aorta of atherosclerotic mice. Our results indicate that cRGD based targeting is more efficient than Col IV-tg-peptide in the early stage of atherosclerosis.

Building collagen IV smart scaffolds on the outside of cells

Collagen IV scaffolds assemble through an intricate pathway that begins intracellularly and is completed extracellularly. Multiple intracellular enzymes act in concert to assemble collagen IV protomers, the building blocks of collagen IV scaffolds. After being secreted from cells, protomers are activated to initiate oligomerization, forming insoluble networks that are structurally reinforced with covalent crosslinks. Within these networks, embedded binding sites along the length of the protomer lead to the "decoration" of collagen IV triple helix with numerous functional molecules. We refer to these networks as "smart" scaffolds, which as a component of the basement membrane enable the development and function of multicellular tissues in all animal phyla. In this review, we present key molecular mechanisms that drive the assembly of collagen IV smart scaffolds.

Role of Hypohalous Acids in Basement Membrane Homeostasis

SIGNIFICANCE

Basement membranes (BMs) are sheet-like structures of specialized extracellular matrix that underlie nearly all tissue cell layers including epithelial, endothelial, and muscle cells. BMs not only provide structural support but are also critical for the development, maintenance, and repair of organs. Animal heme peroxidases generate highly reactive hypohalous acids extracellularly and, therefore, target BMs for oxidative modification. Given the importance of BMs in tissue structure and function, hypohalous acid-mediated oxidative modifications of BM proteins represent a key mechanism in normal development and pathogenesis of disease. Recent Advances: Peroxidasin (PXDN), a BM-associated animal heme peroxidase, generates hypobromous acid (HOBr) to form sulfilimine cross-links within the collagen IV network of BM. These cross-links stabilize BM and are critical for animal tissue development. These findings highlight a paradoxical anabolic role for HOBr, which typically damages protein structure leading to dysfunction.

CRITICAL ISSUES

The molecular mechanism whereby PXDN uses HOBr as a reactive intermediate to cross-link collagen IV, yet avoid collateral damage to nearby BM proteins, remains unclear.

FUTURE DIRECTIONS

The exact identification and functional impact of specific hypohalous acid-mediated modifications of BM proteins need to be addressed to connect these modifications to tissue development and pathogenesis of disease. As seen with the sulfilimine cross-link of collagen IV, hypohalous acid oxidative events may be beneficial in select situations rather than uniformly deleterious. Antioxid. Redox Signal. 27, 839-854.

Collagen IV trafficking: The inside-out and beyond story

Collagen IV networks endow basement membranes (BMs) with remarkable tensile strength and function as morphoregulatory substrata for diverse tissue-specific developmental events. A complex repertoire of intracellular and extracellular molecular interactions are required for collagen IV secretion and supramolecular assembly into BMs. These include intracellular chaperones such as Heat shock protein 47 (Hsp47) and the chaperone-binding trafficking protein Transport and Golgi organization protein 1 (Tango1). Mutations in these proteins lead to compromised collagen IV protomer stability and secretion, leading to defective BM assembly and function. In addition to intracellular chaperones, a role for extracellular chaperones orchestrating the transport, supramolecular assembly, and architecture of collagen IV in BM is emerging. We present evidence derived from evolutionarily distant model organisms that supports an extracellular collagen IV chaperone-like activity for the matricellular protein SPARC (Secreted Protein, Acidic, Rich in Cysteine). Loss of SPARC disrupts BM homeostasis and compromises tissue biomechanics and physiological function. Thus, the combined contributions of intracellular and extracellular collagen IV-associated chaperones and chaperone-like proteins are critical to ensure proper secretion and stereotypic assembly of collagen IV networks in BMs.

Extracellular chloride signals collagen IV network assembly during basement membrane formation

Basement membranes are defining features of the cellular microenvironment; however, little is known regarding their assembly outside cells. We report that extracellular Cl(-) ions signal the assembly of collagen IV networks outside cells by triggering a conformational switch within collagen IV noncollagenous 1 (NC1) domains. Depletion of Cl(-) in cell culture perturbed collagen IV networks, disrupted matrix architecture, and repositioned basement membrane proteins. Phylogenetic evidence indicates this conformational switch is a fundamental mechanism of collagen IV network assembly throughout Metazoa. Using recombinant triple helical protomers, we prove that NC1 domains direct both protomer and network assembly and show in Drosophila that NC1 architecture is critical for incorporation into basement membranes. These discoveries provide an atomic-level understanding of the dynamic interactions between extracellular Cl(-) and collagen IV assembly outside cells, a critical step in the assembly and organization of basement membranes that enable tissue architecture and function. Moreover, this provides a mechanistic framework for understanding the molecular pathobiology of NC1 domains.

Monoclonal Suncus Antibodies: Generation of Fusion Partners to Produce Suncus-Suncus Hybridomas

We used suncus (Suncus murinus; house musk shrew) to generate partner cells for cell fusion to produce suncus monoclonal antibodies. Suncus are insectivores that are genetically distant to rodents, and recognize antigens and epitopes that are not immunogenic in mice and rats, which are the animals most commonly used in basic life science research and from which monoclonal antibodies are usually produced. To date, monoclonal antibodies from suncus have not been generated due to the lack of a plasmacytoma fusion partner. To obtain suncus plasmacytoma cell lines suitable as a cell fusion partner, we injected suncus at both sides of the tail base with antigen emulsion, collected the lymph nodes and spleens, and cultured the cells to obtain immortalized lymphoid cell lines visually resembling mouse SP2/0-Ag14 myeloma cells. Three suncus immunized with the antigen provided 4 cell lines of suncus plasmacytoma, but they did not secrete immunoglobulins. Antibody-producing hybrid cells were generated from these cell lines using a cell fusion technique. Using one of the cell lines as a fusion partner, we obtained six lines of immunoglobulin-producing hybrid cells which secreted an unidentified monoclonal IgG. When these 6 lines were used as new fusion partners, we obtained several hybrid cell lines which secreted immunogen-specific monoclonal antibodies. These hybrid cells can be cloned and cryopreserved. We also obtained another good fusion partner which initially secreted antibody but later stopped doing so. These suncus-suncus hybrid cell lines will be useful for the production of suncus monoclonal antibodies.

Alport syndrome: impact of digenic inheritance in patients management

Alport syndrome (ATS) is a genetically heterogeneous nephropathy with considerable phenotypic variability and different transmission patterns, including monogenic (X-linked/autosomal) and digenic inheritance (DI). Here we present a new series of families with DI and we discuss the consequences for genetic counseling and risk assessment. Out of five families harboring variants in more than one COL4 gene detected by next generation sequencing (NGS), minigene-splicing assay allowed us to identify four as true digenic. Two families showed COL4A3/A4 mutations in cis, mimicking an autosomal dominant inheritance with a more severe phenotype and one showed COL4A3/A4 mutations in trans, mimicking an autosomal recessive inheritance with a less severe phenotype. In a fourth family, a de novo mutation (COL4A5) combined with an inherited mutation (COL4A3) triggered a more severe phenotype. A fifth family, predicted digenic on the basis of silico tools, rather showed monogenic X-linked inheritance due to a hypomorphic mutation, in accordance with a milder phenotype. In conclusion, this study highlights the impact of DI in ATS and explains the associated atypical presentations. More complex inheritance should be therefore considered when reviewing prognosis and recurrence risks. On the other side, these findings emphasize the importance to accompany NGS with splicing assays in order to avoid erroneous identification of at risk members.

Genotype-phenotype correlations in pathology caused by collagen type IV alpha 1 and 2 mutations

COL4A1 and COL4A2 are extracellular matrix proteins that form heterotrimers and are present in nearly all basement membranes in every organ. In the past decade, COL4A1 and COL4A2 mutations have been identified to cause a multi-system disorder for which penetrance and severity of constituent phenotypes can greatly vary. Here, we compare the outcomes of more than 100 mutations identified in patients and data from a murine allelic series to explore the presence of genotype-phenotype correlations - many of which are shared among other types of collagen. We find that there is a frequency bias for COL4A1 over COL4A2 mutations and that glycine (Gly) substitutions within the triple helical domain are the most common class of mutations. Glycine is most often replaced by a charged amino acid, however the position of the mutation, and not the properties of the substituting amino acid, appears to have a greater influence on disease severity. Moreover, the impact of position is not straightforward. Observations from a murine allelic series suggest that mutations in the NC1 domain may result in relatively mild phenotypes via a 'quantitative' mechanism similar to other types of collagens, however, this effect was not apparent in human reports. Importantly, other position-dependent effects had differential impacts depending on the phenotype of interest. For example, the severity of cerebrovascular disease correlated with an amino-to-carboxy severity gradient for triple-helical glycine substitutions whereas the penetrance and severity of myopathy and nephropathy appear to involve a functional sub-domain(s). Greater understanding of genotype-phenotype correlations and the interaction of consequences of different mutations will be important for patient prognosis and care and for developing mechanism-based therapeutics to treat individual components of this emerging syndrome.

Lysyl Oxidase-like-2 Cross-links Collagen IV of Glomerular Basement Membrane

The 7S dodecamer is recognized as an important structural cross-linking domain of collagen IV networks that provide mechanical stability to basement membranes, a specialized form of extracellular matrix essential for the development and maintenance of tissue architecture. Although the 7S dodecamer is stabilized by covalent cross-linking, the molecular mechanism by which such cross-links are formed has not been revealed. Here, we aimed to identify the enzyme(s) that cross-links the 7S dodecamer and characterize its expression in the kidney glomerulus. Pharmacological inhibition of candidate extracellular matrix enzymes revealed that lysyl oxidase activity is required for cross-linking of 7S polypeptides. Among all lysyl oxidase family members, lysyl oxidase-like-2 (LOXL2) was identified as the isoform cross-linking collagen IV in mouse embryonal PFHR-9 cells. Biochemical analyses revealed that LOXL2 readily promoted the formation of lysyl-derived cross-links in the 7S dodecamer but not in the NC1 domain. We also established that LOXL2 is the main lysyl oxidase family member present in the glomerular extracellular matrix. Altogether, we demonstrate that LOXL2 is a novel component of the molecular machinery that forms cross-linked collagen IV networks, which are essential for glomerular basement membrane stability and molecular ultrafiltration function.

Collagen IV diseases: A focus on the glomerular basement membrane in Alport syndrome

Alport syndrome is the result of mutations in any of three type IV collagen genes, COL4A3, COL4A4, or COL4A5. Because the three collagen chains form heterotrimers, there is an absence of all three proteins in the basement membranes where they are expressed. In the glomerulus, the mature glomerular basement membrane type IV collagen network, normally comprised of two separate networks, α3(IV)/α4(IV)/α5(IV) and α1(IV)/α2(IV), is comprised entirely of collagen α1(IV)/α2. This review addresses the current state of our knowledge regarding the consequence of this change in basement membrane composition, including both the direct, via collagen receptor binding, and indirect, regarding influences on glomerular biomechanics. The state of our current understanding regarding mechanisms of glomerular disease initiation and progression will be examined, as will the current state of the art regarding emergent therapeutic approaches to slow or arrest glomerular disease in Alport patients.

Collagen IV diseases: A focus on the glomerular basement membrane in Alport syndrome

Alport syndrome is the result of mutations in any of three type IV collagen genes, COL4A3, COL4A4, or COL4A5. Because the three collagen chains form heterotrimers, there is an absence of all three proteins in the basement membranes where they are expressed. In the glomerulus, the mature glomerular basement membrane type IV collagen network, normally comprised of two separate networks, α3(IV)/α4(IV)/α5(IV) and α1(IV)/α2(IV), is comprised entirely of collagen α1(IV)/α2. This review addresses the current state of our knowledge regarding the consequence of this change in basement membrane composition, including both the direct, via collagen receptor binding, and indirect, regarding influences on glomerular biomechanics. The state of our current understanding regarding mechanisms of glomerular disease initiation and progression will be examined, as will the current state of the art regarding emergent therapeutic approaches to slow or arrest glomerular disease in Alport patients.

COL4A6 is dispensable for autosomal recessive Alport syndrome

Alport syndrome is caused by mutations in the genes encoding α3, α4, or α5 (IV) chains. Unlike X-linked Alport mice, α5 and α6 (IV) chains are detected in the glomerular basement membrane of autosomal recessive Alport mice, however, the significance of this finding remains to be investigated. We therefore generated mice lacking both α3 and α6 (IV) chains and compared their renal function and survival with Col4a3 knockout mice of 129 × 1/Sv background. No significant difference was observed in the renal function or survival of the two groups, or when the mice were backcrossed once to C57BL/6 background. However, the survival of backcrossed double knockout mice was significantly longer than that of the mice of 129 × 1/Sv background, which suggests that other modifier genes were involved in this phenomenon. In further studies we identified two Alport patients who had a homozygous mutation in intron 46 of COL4A4. The α5 and α6 (IV) chains were focally detected in the glomerular basement membrane of these patients. These findings indicate that although α5 and α6 (IV) chains are induced in the glomerular basement membrane in autosomal recessive Alport syndrome, their induction does not seem to play a major compensatory role.

A novel COL4A1 frameshift mutation in familial kidney disease: the importance of the C-terminal NC1 domain of type IV collagen

BACKGROUND

Hereditary microscopic haematuria often segregates with mutations of COL4A3, COL4A4 or COL4A5 but in half of families a gene is not identified. We investigated a Cypriot family with autosomal dominant microscopic haematuria with renal failure and kidney cysts.

METHODS

We used genome-wide linkage analysis, whole exome sequencing and cosegregation analyses.

RESULTS

We identified a novel frameshift mutation, c.4611_4612insG:p.T1537fs, in exon 49 of COL4A1. This mutation predicts truncation of the protein with disruption of the C-terminal part of the NC1 domain. We confirmed its presence in 20 family members, 17 with confirmed haematuria, 5 of whom also had stage 4 or 5 chronic kidney disease. Eleven family members exhibited kidney cysts (55% of those with the mutation), but muscle cramps or cerebral aneurysms were not observed and serum creatine kinase was normal in all individuals tested.

CONCLUSIONS

Missense mutations of COL4A1 that encode the CB3 [IV] segment of the triple helical domain (exons 24 and 25) are associated with HANAC syndrome (hereditary angiopathy, nephropathy, aneurysms and cramps). Missense mutations of COL4A1 that disrupt the NC1 domain are associated with antenatal cerebral haemorrhage and porencephaly, but not kidney disease. Our findings extend the spectrum of COL4A1 mutations linked with renal disease and demonstrate that the highly conserved C-terminal part of the NC1 domain of the α1 chain of type IV collagen is important in the integrity of glomerular basement membrane in humans.

Basement Membranes in the Worm: A Dynamic Scaffolding that Instructs Cellular Behaviors and Shapes Tissues

The nematode worm Caenorhabditis elegans has all the major basement membrane proteins found in vertebrates, usually with a smaller gene family encoding each component. With its powerful forward genetics, optical clarity, simple tissue organization, and the capability to functionally tag most basement membrane components with fluorescent proteins, C. elegans has facilitated novel insights into the assembly and function of basement membranes. Although basement membranes are generally thought of as static structures, studies in C. elegans have revealed their active properties and essential functions in tissue formation and maintenance. Here, we review discoveries from C. elegans development that highlight dynamic aspects of basement membrane assembly, function, and regulation during organ growth, tissue polarity, cell migration, cell invasion, and tissue attachment. These studies have helped transform our view of basement membranes from static support structures to dynamic scaffoldings that play broad roles in regulating tissue organization and cellular behavior that are essential for development and have important implications in human diseases.

HANAC Syndrome Col4a1 Mutation Causes Neonate Glomerular Hyperpermeability and Adult Glomerulocystic Kidney Disease

Hereditary angiopathy, nephropathy, aneurysms, and muscle cramps (HANAC) syndrome is an autosomal dominant syndrome caused by mutations in COL4A1 that encodes the α1 chain of collagen IV, a major component of basement membranes. Patients present with cerebral small vessel disease, retinal tortuosity, muscle cramps, and kidney disease consisting of multiple renal cysts, chronic kidney failure, and sometimes hematuria. Mutations producing HANAC syndrome localize within the integrin binding site containing CB3[IV] fragment of the COL4A1 protein. To investigate the pathophysiology of HANAC syndrome, we generated mice harboring the Col4a1 p.Gly498Val mutation identified in a family with the syndrome. Col4a1 G498V mutation resulted in delayed glomerulogenesis and podocyte differentiation without reduction of nephron number, causing albuminuria and hematuria in newborns. The glomerular defects resolved within the first month, but glomerular cysts developed in 3-month-old mutant mice. Abnormal structure of Bowman's capsule was associated with metalloproteinase induction and activation of the glomerular parietal epithelial cells that abnormally expressed CD44,α-SMA, ILK, and DDR1. Inflammatory infiltrates were observed around glomeruli and arterioles. Homozygous Col4a1 G498V mutant mice additionally showed dysmorphic papillae and urinary concentration defects. These results reveal a developmental role for the α1α1α2 collagen IV molecule in the embryonic glomerular basement membrane, affecting podocyte differentiation. The observed association between molecular alteration of the collagenous network in Bowman's capsule of the mature kidney and activation of parietal epithelial cells, matrix remodeling, and inflammation may account for glomerular cyst development and CKD in patients with COL4A1-related disorders.

Idiopathic epiretinal membrane

BACKGROUND

Idiopathic epiretinal membrane (iERM) is a fibrocellular membrane that proliferates on the inner surface of the retina at the macular area. Membrane contraction is an important sight-threatening event and is due to fibrotic remodeling.

METHODS

Analysis of the current literature regarding the epidemiology, clinical features, and pathogenesis of iERM and fibrotic tissue contraction.

RESULTS

Epidemiologic studies report a relationship between iERM prevalence, increasing age, and posterior vitreous detachment. Clinically, iERM progresses through different stages characterized by an increased thickness and wrinkling of the membrane. Pathophysiologically, iERM formation is a fibrotic process in which myofibroblast formation and the deposition of newly formed collagens play key roles. Anomalous posterior vitreous detachment may be a key event initiating the formation of iERM. The age-related accumulation of advanced glycation end products may contribute to anomalous posterior vitreous detachment formation and may also influence the mechanical properties of the iERM.

CONCLUSION

Remodeling of the extracellular matrix at the vitreoretinal interface by aging and fibrotic changes, plays a significant role in the pathogenesis of iERM. A better understanding of molecular mechanisms underlying this process may eventually lead to the development of effective and nonsurgical approaches to treat and prevent vitreoretinal fibrotic diseases.

Molecular and Genetic Analyses of Collagen Type IV Mutant Mouse Models of Spontaneous Intracerebral Hemorrhage Identify Mechanisms for Stroke Prevention

BACKGROUND

Collagen type IV alpha1 (COL4A1) and alpha2 (COL4A2) form heterotrimers critical for vascular basement membrane stability and function. Patients with COL4A1 or COL4A2 mutations suffer from diverse cerebrovascular diseases, including cerebral microbleeds, porencephaly, and fatal intracerebral hemorrhage (ICH). However, the pathogenic mechanisms remain unknown, and there is a lack of effective treatment.

METHODS AND RESULTS

Using Col4a1 and Col4a2 mutant mouse models, we investigated the genetic complexity and cellular mechanisms underlying the disease. We found that Col4a1 mutations cause abnormal vascular development, which triggers small-vessel disease, recurrent hemorrhagic strokes, and age-related macroangiopathy. We showed that allelic heterogeneity, genetic context, and environmental factors such as intense exercise or anticoagulant medication modulated disease severity and contributed to phenotypic heterogeneity. We found that intracellular accumulation of mutant collagen in vascular endothelial cells and pericytes was a key triggering factor of ICH. Finally, we showed that treatment of mutant mice with a US Food and Drug Administration-approved chemical chaperone resulted in a decreased collagen intracellular accumulation and a significant reduction in ICH severity.

CONCLUSIONS

Our data are the first to show therapeutic prevention in vivo of ICH resulting from Col4a1 mutation and imply that a mechanism-based therapy promoting protein folding might also prevent ICH in patients with COL4A1 and COL4A2 mutations.