Different properties of loss-of-function between variants in the LIPH gene responsible for autosomal recessive woolly hair and further characterization of C3orf52.

BACKGROUND: Autosomal recessive woolly hair (ARWH) is a congenital hair disorder characterized by excessively curled scalp hair with limited growth. One of the causative genes, LIPH encoding PA-PLA1α, is involved in a lipid mediator-dependent signaling, and loss-of-function variants in C3orf52 encoding the transmembrane protein associated with PA-PLA1α, have recently been implicated in ARWH. The pathogenic mechanisms for ARWH, however, remain incompletely understood. OBJECTIVE: To characterize LIPH gene-variants responsible for ARWH and to further clarify the molecular properties of C3orf52. METHODS: Wild-type and five mutant PA-PLA1α (p.W108R, p.H205R, p.C246S, p.H248N, and p.V437Gfs*4), as well as wild-type C3orf52, were overexpressed in cultured cells, and a series of expression and functional analyzes were performed. C3orf52 expression was additionally assessed in human scalp skin sections. RESULTS: We demonstrated that the three mutant PA-PLA1α (p.W108R, p.H205R, and p.V437Gfs*4) were not secreted from the cells and induced more severe endoplasmic reticulum stress. We further showed that only the C-terminal variant p.V437Gfs*4 exhibited a significantly reduced binding affinity to C3orf52, consistent with the finding that PA-PLA1α and C3orf52 interacted via their C-termini. In addition, we confirmed that C3orf52 anchored PA-PLA1α on the plasma membrane in cultured cells. Finally, we showed that secretion of the downstream effector TGF-α via the LPA receptor LPA6 was markedly decreased in cells expressing each of the mutant PA-PLA1α proteins tested. CONCLUSION: Our results indicate that LIPH gene variants cause ARWH through multiple pathogenic pathways, while also providing new insight into the role of C3orf52 in hair follicle development in humans.