Podocyte expression of nonmuscle myosin heavy chain-IIA decreases in idiopathic nephrotic syndrome, especially in focal segmental glomerulosclerosis

MYH9-related disease with a normal platelet count

MYH9-related disease (MYH9-RD) is characterized by congenital macrothrombocytopenia, progressive kidney failure, and sensorineural hearing loss. We describe a patient with MYH9-RD and a normal platelet count. A 13-year-old boy with a normal platelet count presented with proteinuria and hematuria and underwent a kidney biopsy. Light microscopy showed mild mesangial matrix expansion. Electron microscopy showed thinning of the glomerular basement membrane and splitting of the lamina densa. A tentative diagnosis of Alport syndrome was made. Unexpectedly, genetic analysis revealed a de novo MYH9 gene variant (p.Gln1068_Leu1074dup). A peripheral blood smear examination showed giant platelets and leukocyte inclusion bodies, confirming a diagnosis of MYH9-RD. In summary, we described a patient with MYH9-RD without thrombocytopenia who showed glomerular basement membrane abnormalities similar to Alport syndrome. Peripheral blood smear examinations may be helpful for an appropriate diagnosis of MYH9-RD, even in patients with proteinuria and a normal platelet count.

MYH9-related disorder with sole presentation of end-stage kidney disease and long-term, recurrence-free living after living donor renal transplantation: a case report

MYH9-related disorders are a group of autosomal dominant disorders caused by mutations in MYH9, and are characterized by thrombocytopenia, sensorineural hearing loss, cataracts, and renal failure. Here, we report a case of chronic renal failure due to MYH9-related disorder with renal symptoms in a patient who underwent living-donor renal transplantation. The patient was diagnosed with proteinuria during a health checkup at the age of 12 years. Her renal function gradually deteriorated, and hemodialysis was initiated at 34 years of age. No definitive diagnosis of renal disease was made through renal biopsy. At the age of 35, she underwent living-donor renal transplantation from her mother as the donor. Six years after transplantation, her renal function remained stable, and no evidence of recurrent nephritis was found during renal biopsies. The family history revealed that her father, uncle, and younger brother had end-stage kidney disease. Genetic testing revealed a mutation (p.E1653D) related to the MYH9 gene. As her father had a history of renal biopsy and was diagnosed with focal segmental glomerulosclerosis (FSGS), we diagnosed chronic renal failure due to FSGS associated with MYH9 disorder. There were no findings suggestive of hearing loss, cataracts, or thrombocytopenia in the recipient or their family members with renal failure, and no symptoms other than renal failure were noted.

FilGAP controls cell-extracellular matrix adhesion and process formation of kidney podocytes

The function of kidney podocytes is closely associated with actin cytoskeleton regulated by Rho small GTPases. Loss of actin-driven cell adhesions and processes is connected to podocyte dysfunction, proteinuria, and kidney diseases. FilGAP, a GTPase-activating protein for Rho small GTPase Rac1, is abundantly expressed in kidney podocytes, and its gene is linked to diseases in a family with focal segmental glomerulosclerosis. In this study, we have studied the role of FilGAP in podocytes in vitro. Depletion of FilGAP in cultured podocytes induced loss of actin stress fibers and increased Rac1 activity. Conversely, forced expression of FilGAP increased stress fiber formation whereas Rac1 activation significantly reduced its formation. FilGAP localizes at the focal adhesion (FA), an integrin-based protein complex closely associated with stress fibers, that mediates cell-extracellular matrix (ECM) adhesion, and FilGAP depletion decreased FA formation and impaired attachment to the ECM. Moreover, in unique podocyte cell cultures capable of inducing the formation of highly organized processes including major processes and foot process-like projections, FilGAP depletion or Rac1 activation decreased the formation of these processes. The reduction of FAs and process formations in FilGAP-depleted podocyte cells was rescued by inhibition of Rac1 or P21-activated kinase 1 (PAK1), a downstream effector of Rac1, and PAK1 activation inhibited their formations. Thus, FilGAP contributes to both cell-ECM adhesion and process formation of podocytes by suppressing Rac1/PAK1 signaling.

Renal Biopsy-induced Hematoma and Infection in a Patient with Asymptomatic May-Hegglin Anomaly

The May-Hegglin anomaly is characterized by inherited thrombocytopenia, giant platelets, and leukocyte cytoplasmic inclusion bodies. The Fechtner, Sebastian, and Epstein syndromes are associated with mutations of the MYH9-coding nonmuscle myosin heavy chain ⅡA, similar to the May-Hegglin anomaly, and are together classified as MYH9 disorders. MYH9 disorders may include symptoms of Alport syndrome, including nephritis and auditory and ocular disorders. A 6-year-old boy was diagnosed with an MYH9 disorder after incidental discovery of hematuria and proteinuria. Focal segmental glomerulosclerosis was detected on renal biopsy. However, despite no prior bleeding diatheses, he developed a large post-biopsy hematoma despite a preprocedural platelet transfusion calculated to increase the platelet count from 54,000/μL to >150,000/μL. Idiopathic thrombocytopenic purpura is a major cause of pediatric thrombocytopenia following acute infection or vaccination, and patients with MYH9 disorders may be misdiagnosed with idiopathic thrombocytopenic purpura and inappropriately treated with corticosteroids. Careful differential diagnosis is important in thrombocytopenic patients with hematuria and proteinuria for the early detection of thrombocytopenia. Patients with MYH9 disorders require close follow-up and treatment with angiotensin Ⅱ receptor blockers to prevent the onset of progressive nephritis, which may necessitate hemodialysis or renal transplantation. The need for renal biopsy in patients with MYH9 disorders should be carefully considered because there could be adverse outcomes even after platelet transfusion.

Conditional Myh9 and Myh10 inactivation in adult mouse renal epithelium results in progressive kidney disease

Actin-associated nonmuscle myosin II (NM2) motor proteins play critical roles in a myriad of cellular functions, including endocytosis and organelle transport pathways. Cell type–specific expression and unique subcellular localization of the NM2 proteins, encoded by the Myh9 and Myh10 genes, in the mouse kidney tubules led us to hypothesize that these proteins have specialized functional roles within the renal epithelium. Inducible conditional knockout (cKO) of Myh9 and Myh10 in the renal tubules of adult mice resulted in progressive kidney disease. Prior to overt renal tubular injury, we observed intracellular accumulation of the glycosylphosphatidylinositol-anchored protein uromodulin (UMOD) and gradual loss of Na⁺ K⁺ 2Cl^– cotransporter from the apical membrane of the thick ascending limb epithelia. The UMOD accumulation coincided with expansion of endoplasmic reticulum (ER) tubules and activation of ER stress and unfolded protein response pathways in Myh9&10-cKO kidneys. We conclude that NM2 proteins are required for localization and transport of UMOD and loss of function results in accumulation of UMOD and ER stress–mediated progressive renal tubulointerstitial disease. These observations establish cell type–specific role(s) for NM2 proteins in regulation of specialized renal epithelial transport pathways and reveal the possibility that human kidney disease associated with MYH9 mutations could be of renal epithelial origin.

Adult mouse renal epithelium specific knockout of Myh9 and Myh10 genes result in kidney disease.

Effect of donor non-muscle myosin heavy chain (MYH9) gene polymorphisms on clinically relevant kidney allograft dysfunction

BACKGROUND

Despite its established association with chronic kidney disease (CKD) the role of myosin-9 (MYH9) gene variation on transplanted kidney function remains unknown. This study aimed at evaluating the effect of donor MYH9 nephrogenic variants on renal allograft function within the first post transplantation year.

METHODS

In the longitudinal kidney transplant study 207 deceased donors were genotyped for previously known risk MYH9 single nucleotide polymorphisms (SNPs). The predictor was MYH9 high-risk variants status. The primary outcome was mean eGFR found in low vs. high risk MYH9 genotypes between third and twelfth post-transplant month, the secondary outcome was the risk of proteinuria.

RESULTS

Distribution of genotypes remained in Hardy-Weinberg equilibrium. The T allele of rs3752462 (dominant model, TT or TC vs. CC) was associated with higher filtration rate (P = 0.05) in a multivariate analysis after adjusting for delayed graft function and donor sex. Two G alleles of rs136211 (recessive model, GG vs. GA or AA) resulted in doubling the risk of proteinuria (OR = 2.22; 95% CI = 1.18-4.37, P = 0.017) after adjusting for donor and recipient sex.

CONCLUSION

Deceased donor kidneys of European descent harboring MYH9 SNPs rs3752462 T allele show significantly superior estimated filtration rate while those of rs136211 GG genotype excessive risk of proteinuria. These findings, if replicated, may further inform and improve individualization of allocation and treatment policies.

Non-Muscle Myosin 2A (NM2A): Structure, Regulation and Function

Non-muscle myosin 2A (NM2A) is a motor cytoskeletal enzyme with crucial importance from the early stages of development until adulthood. Due to its capacity to convert chemical energy into force, NM2A powers the contraction of the actomyosin cytoskeleton, required for proper cell division, adhesion and migration, among other cellular functions. Although NM2A has been extensively studied, new findings revealed that a lot remains to be discovered concerning its spatiotemporal regulation in the intracellular environment. In recent years, new functions were attributed to NM2A and its activity was associated to a plethora of illnesses, including neurological disorders and infectious diseases. Here, we provide a concise overview on the current knowledge regarding the structure, the function and the regulation of NM2A. In addition, we recapitulate NM2A-associated diseases and discuss its potential as a therapeutic target.

Two Cases of the MYH9 Disorder Fechtner Syndrome Diagnosed from Observation of Peripheral Blood Cells before End-Stage Renal Failure

As a MYH9 disorder, Fechtner syndrome is characterized by nephritis, giant platelets, granulocyte inclusion bodies (Döhle-like bodies), cataract, and sensorineural deafness. Observation of peripheral blood smear for the presence of thrombocytopenia, giant platelets, and granulocyte inclusion bodies (Döhle-like bodies) is highly important for the early diagnosis of MYH9 disorders. In our two cases, sequencing analysis of the MYH9 gene indicated mutations in exon 24. Both cases were diagnosed as the MYH9 disorders Fechtner syndrome before end-stage renal failure on the basis of the observation of peripheral blood smear.

Nonmuscle myosin 2 proteins encoded by Myh9, Myh10, and Myh14 are uniquely distributed in the tubular segments of murine kidney

The diverse epithelial cell types of the kidneys are segregated into nephron segments and the collecting ducts in order to endow each tubular segment with unique functions. The rich diversity of the epithelial cell types is highlighted by the unique membrane channels and receptors expressed within each nephron segment. Our previous work identified a critical role for Myh9 and Myh10 in mammalian endocytosis. Here, we examined the expression patterns of Nonmuscle myosin 2 (NM2) heavy chains encoded by Myh9, Myh10, and Myh14 in mouse kidneys as these genes may confer unique nephron segment‐specific membrane transport properties. Interestingly, we found that each segment of the renal tubules predominately expressed only two of the three NM2 isoforms, with isoform‐specific subcellular localization, and different levels of expression within a nephron segment. Additionally, we identify Myh14 to be restricted to the intercalated cells and Myh10 to be restricted to the principal cells within the collecting ducts and connecting segments. We speculate that the distinct expression pattern of the NM2 proteins likely reflects the diversity of the intracellular trafficking machinery present within the different renal tubular epithelial segments.

Injury-induced actin cytoskeleton reorganization in podocytes revealed by super-resolution microscopy

The architectural integrity of tissues requires complex interactions, both between cells and between cells and the extracellular matrix. Fundamental to cell and tissue homeostasis are the specific mechanical forces conveyed by the actomyosin cytoskeleton. Here we used super-resolution imaging methods to visualize the actin cytoskeleton in the kidney glomerulus, an organized collection of capillaries that filters the blood to make the primary urine. Our analysis of both mouse and human glomeruli reveals a network of myosin IIA-containing contractile actin cables within podocyte cell bodies and major processes at the outer aspects of the glomerular tuft. These likely exert force on an underlying network of myosin IIA-negative, noncontractile actin fibers present within podocyte foot processes that function to both anchor the cells to the glomerular basement membrane and stabilize the slit diaphragm against the pressure of fluid flow. After injuries that disrupt the kidney filtration barrier and cause foot process effacement, the podocyte's contractile actomyosin network relocates to the basolateral surface of the cell, manifesting as sarcomere-like structures juxtaposed to the basement membrane. Our findings suggest a new model of the podocyte actin cytoskeleton in health and disease and suggest the existence of novel mechanisms that regulate podocyte architecture.

The role of Slit-Robo signaling in the regulation of tissue barriers

The role of Slit/Robo signaling has extended from initial axon repulsion in the developing nervous system to organ morphogenesis, cancer development and angiogenesis. Slit/Robo signaling regulates similar pathways within these processes. Slit/Robo ensures the homeostasis of the dynamic interaction between cell-cell and cell-matrix interactions. The dysregulation of Slit/Robo signaling damages the tissue barrier, resulting in developmental abnormalities or disease. Here, we summarize how Slit/Robo controls kidney morphogenesis and describe the dual roles of Slit/Robo signaling in the regulation of tumorigenesis and angiogenesis.

Gene expression profiling to identify the toxicities and potentially relevant human disease outcomes associated with environmental heavy metal exposure

Heavy metals are the most commonly encountered toxic substances that increase susceptibility to various diseases after prolonged exposure. We have previously shown that healthy volunteers living near a mining area had significant contamination with heavy metals associated with significant changes in the expression of some detoxifying genes, xenobiotic metabolizing enzymes, and DNA repair genes. However, alterations of most of the molecular target genes associated with diseases are still unknown. Thus, the aims of this study were to (a) evaluate the gene expression profile and (b) identify the toxicities and potentially relevant human disease outcomes associated with long-term human exposure to environmental heavy metals in mining area using microarray analysis. For this purpose, 40 healthy male volunteers who were residents of a heavy metal-polluted area (Mahd Al-Dhahab city, Saudi Arabia) and 20 healthy male volunteers who were residents of a non-heavy metal-polluted area were included in the study. Total RNA was isolated from whole blood using PAXgene Blood RNA tubes and then reversed transcribed and hybridized to the gene array using the Affymetrix U219 GeneChip. Microarray analysis showed about 2129 genes were identified and differentially altered, among which a shared set of 425 genes was differentially expressed in the heavy metal-exposed groups. Ingenuity pathway analysis revealed that the most altered gene-regulated diseases in heavy metal-exposed groups included hematological and developmental disorders and mostly renal and urological diseases. Quantitative real-time polymerase chain reaction closely matched the microarray data for some genes tested. Importantly, changes in gene-related diseases were attributed to alterations in the genes encoded for protein synthesis. Renal and urological diseases were the diseases that were most frequently associated with the heavy metal-exposed group. Therefore, there is a need for further studies to validate these genes, which could be used as early biomarkers to prevent renal injury.

Non-muscle myosin II in disease: mechanisms and therapeutic opportunities

The actin motor protein non-muscle myosin II (NMII) acts as a master regulator of cell morphology, with a role in several essential cellular processes, including cell migration and post-synaptic dendritic spine plasticity in neurons. NMII also generates forces that alter biochemical signaling, by driving changes in interactions between actin-associated proteins that can ultimately regulate gene transcription. In addition to its roles in normal cellular physiology, NMII has recently emerged as a critical regulator of diverse, genetically complex diseases, including neuronal disorders, cancers and vascular disease. In the context of these disorders, NMII regulatory pathways can be directly mutated or indirectly altered by disease-causing mutations. NMII regulatory pathway genes are also increasingly found in disease-associated copy-number variants, particularly in neuronal disorders such as autism and schizophrenia. Furthermore, manipulation of NMII-mediated contractility regulates stem cell pluripotency and differentiation, thus highlighting the key role of NMII-based pharmaceuticals in the clinical success of stem cell therapies. In this Review, we discuss the emerging role of NMII activity and its regulation by kinases and microRNAs in the pathogenesis and prognosis of a diverse range of diseases, including neuronal disorders, cancer and vascular disease. We also address promising clinical applications and limitations of NMII-based inhibitors in the treatment of these diseases and the development of stem-cell-based therapies.

Potential signal pathway of all-trans retinoic acid for MMP-2 and MMP-9 expression in injury podocyte induced by adriamycin

All-trans-retinoic acid (ATRA) can regulate some specific genes expression in various tissue and cells via nuclear retinoic acid receptors (RARs), including three subtypes: retinoic acid receptor-alpha (RAR-α), retinoic acid receptor-beta (RAR-β) and retinoic acid receptor-gamma (RAR-γ). Podocyte injury plays a pivotal role in the progression of glomerulosclerosis (GS). This study was performed to study the potential signal pathway of ATRA in the expression of matrix metalloproteinases-2 (MMP-2) and matrix metalloproteinases-9 (MMP-9) in injury podocyte. Cells were divided into three groups: group of negative control (NC), group of injury podocyte induced by adriamycin (ADR) (AI) and group of ADR inducing podocyte injury model treated with ATRA (AA). The cells morphology changes were detected using microscope and scanning electron microscopy. MMP-2 and MMP-9 enzymic activity was detected using the gelatin zymography method. Protein and mRNA expressions of MMP-2, MMP-9, RAR-α, RAR-β and RAR-γ were measured by western-blot and real-time RT-PCR. Enzymatic activity of MMP-2 and MMP-9 in group AA was significantly enhanced compared to AI group after ATRA-treated 24 h (p < 0.05). The protein and mRNA expressions of MMP-2/MMP-9 in group AA were significantly increased than those in group AI at both 12 and 24 h time points (p < 0.05). Compared to group AI, RAR-α and RAR-γ protein/mRNA expressions of group AA were significantly increased at both 12 and 24 h time points (p < 0.05). There was no difference for the expression of RAR-β between group AI and group AA (p > 0.05). RAR-α protein level was positively correlated with MMP-2 or MMP-9 protein expression (p < 0.05), and RAR-γ protein level was also positively correlated with MMP-2 or MMP-9 protein expression (p < 0.05). In conclusion, ATRA may increase expression of MMP-2 and MMP-9 by the potential signal pathway of RAR-α and RAR-γ in injury podocyte induced by adriamycin, but not RAR-β.