Mutations in the canonical transient receptor potential cation channel 6 (TRPC6) are responsible for familial forms of adult onset focal segmental glomerulosclerosis (FSGS). The mechanisms by which TRPC6 mutations cause kidney disease are not well understood. We used TRPC6-deficient mice to examine the function of TRPC6 in the kidney. We found that adult TRPC6-deficient mice had BP and albumin excretion rates similar to wild-type animals. Glomerular histomorphology revealed no abnormalities on both light and electron microscopy. To determine whether the absence of TRPC6 would alter susceptibility to hypertension and renal injury, we infused mice with angiotensin II continuously for 28 days. Although both groups developed similar levels of hypertension, TRPC6-deficient mice had significantly less albuminuria, especially during the early phase of the infusion; this suggested that TRPC6 adversely influences the glomerular filter. We used whole-cell patch-clamp recording to measure cellmembrane currents in primary cultures of podocytes from both wild-type and TRPC6-deficient mice. In podocytes from wild-type mice, angiotensin II and a direct activator of TRPC6 both augmented cellmembrane currents; TRPC6 deficiency abrogated these increases in current magnitude. Our findings suggest that TRPC6 promotes albuminuria, perhaps by promoting angiotensin II-dependent increases in Ca 2ϩ , suggesting that TRPC6 blockade may be therapeutically beneficial in proteinuric kidney disease. The transient receptor potential (TRP) ion channel family is a diverse group of cation channels identified by a common primary structure with six membrane-spanning domains and intracellular carboxy and amino termini. Within the larger group of TRP channels, the TRPC family is characterized by three or four amino-terminal ankyrin repeats and a highly conserved TRP domain. Within the TRPC family, TRPC6 is 75% homologous at the amino acid level with TRPC3 and TRPC7, and all three are activated by diacylglycerol. They are believed to associate as heterotrimers to form functional ion channels on the cell surface. 1 A role for TRPC6 in the kidney was revealed by studies showing that mutations in the TRPC6 gene cause autosomal dominant forms of hereditary focal segmental glomerulosclerosis (FSGS) that are particularly aggressive. We originally reported that patients with the TRPC6 P112Q mutation developed high-grade proteinuria by the third or fourth decade of life, and 60% progressed to ESRD. 2 We also found augmented intracellular calcium (Ca 2ϩ ) influx with TRPC6 P112Q compared with wild-type

Focal and segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome in children and adults throughout the world. In the past 50 years, significant advances have been made in the identification and characterization of familial forms of nephrotic syndrome and FSGS. Resultant to these pursuits, several podocyte structural proteins such as nephrin, podocin, alpha-actinin 4 (ACTN4), and CD2-associated protein (CD2AP) have emerged to provide critical insight into the pathogenesis of hereditary nephrotic syndromes. The latest advance in familial FSGS has been the discovery of a mutant form of canonical transient receptor potential cation channel 6 (TRPC6), which causes an increase in calcium transients and essentially a gain of function in this cation channel located on the podocyte cell membrane. The TRP ion channel family is a diverse group of cation channels united by a common primary structure which contains six membrane-spanning domains, with both carboxy and amino termini located intracellularly. TRP channels are unique in their ability to activate independently of membrane depolarization. TRPC6 channels have been shown to be activated via phospholipase C stimulation. The mechanisms by which mutant TRPC6 causes an increase in intracellular calcium and leads to glomerulosclerosis are unknown. Mutant TRPC6 may affect critical interactions with the aforementioned podocyte structural proteins, leading to abnormalities in the slit diaphragm or podocyte foot processes. Mutant TRPC6 may also amplify injurious signals mediated by Ang II, a common final pathway of podocyte apoptosis in various mammalian species. Current evidence also suggests that blocking TRPC6 channels may be of therapeutic benefit in idiopathic FSGS, a disease with a generally poor prognosis. Preliminary experiments reveal the commonly used immunosuppressive agent FK-506 can inhibit TRPC6 activity in vivo. This creates the exciting possibility that blocking TRPC6 channels within the podocyte may translate into long-lasting clinical benefits in patients with FSGS.

Focal and segmental glomerulosclerosis (FSGS) is the most common glomerular cause of endstage kidney disease (ESKD). The etiology of FSGS has not been fully elucidated; recent results from the positional cloning of genes mutated in nephrotic syndromes are now beginning to provide insight into the pathogenesis of these diseases. Mutations in PLCE1/NPHS3 were recently reported as a cause of nephrotic syndrome characterized by diffuse mesangial sclerosis (DMS) histology. One single family with a missense mutation had late onset of the disease that was characterized by FSGS. To further define the role of PLCE1 mutations in the etiology of FSGS, we performed mutational analysis in 69 families with FSGS.Results-A total of 69 families with 231 affected individuals were examined. The median age of disease onset was 26 years (range 1-66). Onset of ESKD was a median of 35.5 years. Seven variants leading to non-synonymous changes were found, of these, only two were new variants (exon4 c.1682 G>A R561Q, exon31 c.6518A>G K2173R). No known disease-causing mutations were identified in the families screened.Conclusion-PLCE1/NPHS3 mutations are not a cause of FSGS in this cohort. Absence of mutations in PLCE1/NPHS3 in this study indicates that there are additional genetic causes of FSGS and that hereditary FSGS is a heterogeneous disease. Kindreds appropriate for genomewide screening will be subjected to analysis to identify other genetic causes of FSGS.