Expression of mRNA for type IV collagen α1, α5 and α6 chains by cultured dermal fibroblasts from patients with X-linked Alport syndrome

COL4A5 mutations causing X-linked Alport syndrome (XLAS) are frequently associated with absence of the α3, α4, α5 and α6 chains of type IV collagen from basement membranes and increased amounts of the α1(IV) and α2(IV) chains in glomerular basement membrane. Although many COL4A5 mutations have been described in XLAS, the mechanisms by which these mutations influence the basement membrane appearance of chains other than α5(IV) remain poorly understood. In this study, we used dermal fibroblasts from eight normal individuals and nine males with XLAS to test the hypotheses that COL4A5 mutations increase transcription of COL4A1 and suppress transcription of COL4A6. Ribonuclease protection assays revealed that α1(IV), α5(IV) and α6(IV) transcripts were expressed in cultures of dermal fibroblasts. The mRNA levels for α1(IV) in eight of nine patients with XLAS were not increased compared to controls; one patient with a large COL4A5 deletion showed significant elevation of α1(IV) mRNA levels. No differences in steady-state mRNA levels for α6(IV) were found when XLAS fibroblasts were compared with controls, even though little or no α6(IV) protein was detectable at the dermal-epidermal junction by immunofluorescence study. This finding suggests that post-transcriptional events account for the absence of α6(IV) in the Alport dermal-epidermal junction.