Advances in the biology and genetics of the podocytopathies: implications for diagnosis and therapy

Genetic Susceptibility to Chronic Kidney Disease: Links, Risks and Management

Chronic kidney disease (CKD) is associated with significant morbidity and mortality worldwide. In recent years, our understanding of genetic causes of CKD has expanded significantly with several renal conditions having been identified. This review discusses the current landscape of genetic kidney disease and their potential treatment options. This review will focus on cystic kidney disease, glomerular disease with genetic associations, congenital anomalies of kidneys and urinary tract (CAKUT), autosomal dominant-tubulointerstitial kidney disease (ADTKD), inherited nephrolithiasis and nephrocalcinosis.

High glucose reduces expression of podocin in cultured human podocytes by stimulating TRPC6

The transient receptor potential canonical 6 (TRPC6) channel and podocin are colocalized in the glomerular slit diaphragm as an important complex to maintain podocyte function. Gain of TRPC6 function and loss of podocin function induce podocyte injury. We have previously shown that high glucose induces apoptosis of podocytes by activating TRPC6; however, whether the activated TRPC6 can alter podocin expression remains unknown. Western blot analysis and confocal microscopy were used to examine both expression levels of TRPC6, podocin, and nephrin and morphological changes of podocytes in response to high glucose. High glucose increased the expression of TRPC6 but reduced the expression of podocin and nephrin, in both cultured human podocytes and type 1 diabetic rat kidneys. The decreased podocin was diminished in TRPC6 knockdown podocytes. High glucose elevated intracellular Ca²⁺ in control podocytes but not in TRPC6 knockdown podocytes. High glucose also elevated the expression of a tight junction protein, zonula occludens-1, and induced the redistribution of zonula occludens-1 and loss of podocyte processes. These data together suggest that high glucose reduces protein levels of podocin by activating TRPC6 and induces morphological changes of cultured podocytes.

Comprehensive and Systematic Analysis of Gene Expression Patterns Associated with Body Mass Index

Both genetic and environmental factors are suggested to influence overweight and obesity risks. Although individual loci and genes have been frequently shown to be associated with body mass index (BMI), the overall interaction of these genes and their role in BMI remains underexplored. Data were collected in 90 healthy, predominately Caucasian participants (51% female) with a mean age of 26.00 ± 9.02 years. Whole blood samples were assayed by Affymetrix GeneChip Human Genome U133 Plus 2.0 Array. We integrated and analyzed the clinical and microarray gene expression data from those individuals to understand various systematic gene expression patterns underlying BMI. Conventional differential expression analysis identified seven genes RBM20, SEPT12, AX748233, SLC30A3, WTIP, CASP10, and OR12D3 associated with BMI. Weight gene co-expression network analysis among 4,647 expressed genes identified two gene modules associated with BMI. These two modules, with different extents of gene connectivity, are enriched for catabolic and muscle system processes respectively, and tend to be regulated by zinc finger transcription factors. A total of 246 hub genes were converted to non-hub genes, and 286 non-hub genes were converted to hub genes between normal and overweight individuals, revealing the network dynamics underlying BMI. A total of 28 three-way gene interactions were identified, suggesting the existence of high-order gene expression patterns underlying BMI. Our study demonstrated a variety of systematic gene expression patterns associated with BMI and thus provided novel understanding regarding the genetic factors for overweight and obesity risks on system levels.

Expression patterns of podocyte-associated mRNAs in patients with proliferative or non-proliferative glomerulopathies

AIM

It is not clear how the podocyte damage manifests in different glomerulopathies. This study evaluated the podocyte-associated mRNA profiles in renal tissue and urine of patients with proliferative (PGs) or non-proliferative (NPGs) glomerulopathies.

METHODS

Messenger RNA levels of nephrin, podocin, podocalyxin, synaptopodin, and alpha-actinin-4 were measured in the kidney tissue and urinary cells by real-time polymerase chain reaction. Podocyte-associated mRNAs were correlated with proteinuria and renal function, and the effect of immunosuppressive treatment of PGs and NPGs on urine mRNAs was assessed up to one year of follow up.

RESULTS

Podocyte-associated mRNAs were expressed consistently less in kidney tissue from patients with NPGs, and urinary podocyte mRNA levels were significantly higher in the PG group. After six months of immunosuppressive therapy, patients with PGs showed a significant reduction in the expression of podocin, podocalyxin, and alpha-actinin-4 compared with baseline (p<0.001). In the NPG group, alpha-actinin-4 levels decreased (p=0.008), and there was also a trend toward reduced podocalyxin mRNA (p=0.08). Urine podocyte-associated mRNAs correlated with the level of proteinuria at baseline and at six months, and there was a trend toward an inverse correlation between urinary mRNAs and kidney function at one year of follow up.

CONCLUSIONS

Podocyte-associated mRNAs were inhibited in kidney tissue concomitantly with their increase in urine in these patients with glomerulopathies. Different profiles of mRNA expression were seen, pointing to a higher degree of intra-renal podocytopenia in the NPGs and of podocyturia in the PGs. The immunosuppressive therapy effectively reduced the urinary levels of podocyte-associated mRNAs.

Primary focal and segmental glomerulosclerosis and soluble factor urokinase-type plasminogen activator receptor

Primary focal and segmental glomerulosclerosis (FSGS) may be due to genetic or acquired etiologies and is a common cause of nephrotic syndrome with high morbidity that often leads to end-stage renal failure. The different available therapeutic approaches are unsuccessful, in part due to partially deciphered heterogeneous and complex pathophysiological mechanisms. Moreover, the term FSGS, even in its primary form, comprises a histological description shared by a number of different causes with completely different molecular pathways of disease. This review focuses on the latest developments regarding the pathophysiology of primary acquired FSGS caused by soluble factor urokinase type plasminogen activator receptor, a circulating permeability factor involved in proteinuria and edema formation, and describes recent advances with potential success in therapy.