Inhibition of MAFB and PI3K/AKT Signaling for Hereditary FSGS with Multicentric Carpotarsal Osteolysis.
KEY POINTS: Multicentric carpotarsal osteolysis, a rare disorder, causes progressive osteolysis and kidney failure because of v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB) gene mutations. A genome-edited mouse model carrying the multicentric carpotarsal osteolysis mutation was used to obtain a deeper understanding of this rare disease. Targeting MAFB/IGF-1/PI3K/AKT signaling may provide new treatments for multicentric carpotarsal osteolysis-related nephropathy. BACKGROUND: Multicentric carpotarsal osteolysis (MCTO) is a rare condition characterized by progressive osteolysis and often kidney failure. It is caused by autosomal dominant mutations in the transcription factor v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog B ( MAFB ). METHODS: Given the absence of efficacious therapeutic interventions for MCTO and the obscurity of its pathophysiologic mechanisms, we used mice with the MCTO mutation ( MafbMCTO/MCTO mice) to explore the role of MAFB. RESULTS: MafbMCTO/MCTO mice displayed FSGS, mirroring the manifestations seen in patients with MCTO. These mice showed that the MCTO mutation leads to the accumulation of MAFB protein. Heterozygous MafbMCTO/- mice, generated by crossbreeding to reduce MAFB levels, neither exhibited albuminuria nor showed any histologic abnormalities in the kidney, suggesting that excess MAFB was detrimental. We subsequently conducted RNA-seq on the glomeruli from MafbMCTO/MCTO mice and detected pronounced upregulation of the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway through IGF-1. Given that receptor tyrosine kinases activate PI3K/AKT, we treated MafbMCTO/MCTO mice with the inhibitor imatinib. This led to a significant decline in urinary albumin levels compared with the control group. CONCLUSIONS: Our findings demonstrate that the MCTO mutation resulted in MAFB protein accumulation and led to the development of FSGS in mice.