Chemical chaperone 4-phenylbutyrate treatment alleviates the kidney phenotype in a mouse model of Alport syndrome with a pathogenic variant in Col4a3

Abstract

Introduction: Alport Syndrome is a severe inherited glomerulopathy caused by pathogenic variants in genes encoding collagen-IV, the most abundant component of the glomerular basement membrane. Patients with Alport lack effective therapies beyond blockade of the renin-angiotensin-aldosterone system. Here, we test 4-phenylbutyrate (4-PBA) and tauroursodeoxycholic acid (TUDCA), two chemical chaperones, to rescue mouse models of a later-onset Alport Syndrome.

Methods: Knock-in mice bearing the Col4a3:p.Gly1332Glu pathogenic substitution in homozygosity and a compound heterozygous model bearing the same variant and the knockout allele were used. Mice received chaperones either for short or long-term periods. Also we examined the expression and secretion of mutant α3 chains in primary cultured mouse podocytes.

Results: TUDCA-treated Alport mice did not differ from the placebo-treated group. However, mice treated with 4-PBA demonstrated considerable improvement in the morphology and structure of glomerular basement membranes compared with control placebo-treated mice. Electron microscopy showed a 54% reduction of lesions and significant decline of lesion severity in the basement membrane of treated Alport mice. Additionally, treatment with 4-PBA reduced interstitial fibrosis, global and segmental glomerulosclerosis, while proteinuria and hematuria remained at low levels in Alport mice. In-vivo findings and in-vitro inhibition of the proteasome in primary cultured podocytes indicate that mutant collagen is reduced within the glomeruli of mutant mice, likely due to proteasomal degradation of misfolded collagen. Importantly, treatment of mice and cultured podocytes with 4-PBA improved secretion and incorporation of collagen IV into extracellular matrix probably by enhancing trimer folding.

Conclusions: Our results suggest a therapeutic potential for 4-PBA in combating kidney dysfunction in Alport syndrome.

Keywords: 4-PBA chaperone; Alport syndrome; chronic kidney disease; collagen-IV; mouse model; repurposing.