Objective: Mutations in the TRPC6 gene are responsible for a late onset form of familial focal segmental glomerulosclerosis (FSGS). However, the role of TRPC6 variation in Chinese patients with late onset familial FSGS remains unclear. Here, we screened 31 Chinese pedigrees with late onset familial FSGS for changes in TRPC6 by DNA sequence analysis.
Methods: Genomic DNA was extracted from peripheral leukocytes. We PCR-amplified each of 13 exons of TRPC6 for sequence analysis. When a novel nucleotide change seemed likely to cause FSGS, we carried out an in vitro research to determine the effects of the mutation on TRPC6 function. HEK 293 cells were transfected stably with vectors containing mutant or wild type TRPC6 cDNA. We then compared the expression of mutant TRPC6 to wild type TRPC6 using Western blot. For the observation of the function of mutant TRPC6 channel compared with wild type TRPC6 channel, Intracellular Ca(2+) concentration was detected using fluorescent indicator Fluo-3 among different groups of cells upon stimulation with 1-oleoyl-2-acetyl sn-glycerol (OAG).
Results: All the 31 pedigrees with late onset familial FSGS were collected in our department from September 1997 to October 2007. A novel TRPC6 mutation (cytosine 2664 adenine resulting in Glutamine 889 Lysine substitution, Q889K) was identified in one of these pedigrees. Mutant TRPC6 (TRPC6(Q889K)) or wild type TRPC6 was stably expressed in HEK293 cells by Western blot. The mutant TRPC6 expression was a little increased without significant difference compared with wild type TRPC6 expression, whereas the intracellular Ca(2+) level in cells expressing mutant TRPC6 was significantly increased compared with that in the cells expressing wild TRPC6 upon stimulation.
Conclusion: We identified a novel TRPC6 mutation Q889K associated with late onset FFSGS in Chinese pedigrees and this mutation was demonstrated to be "gain of function" by an in vitro functional research.