Novel susceptibility gene SLC23A2 functions via PI3K-AKT-mTOR pathway in etiology of non-syndromic cleft palate

The biological interactions between genetic and environmental modifiers play critical roles in the etiology of non-syndromic orofacial cleft (NSOC), but it is rarely studied. This study selected 47 environmental related genes from the metabolic pathways of smoking, drinking, hypoxia, and vitamins (including vitamin A, vitamin B9 (folic acid), vitamin C (ascorbic acid), vitamin D, and vitamin E), and test their associations with NSOC and its subtypes. We found that a novel gene SLC23A2, the vitamin C transporter gene is significantly associated with non-syndromic cleft palate only (NSCPO) (p = 3.25E-07, OR = 8.45, 95%CI:3.73-19.17). SLC23A2 is expressed in the craniofacial region of zebrafish (24hpf to 120hpf), obvious craniofacial abnormalities appeared in zebrafish (48hpf) when knock down the slc23a2 (slc23a2-MO). Knock down SLC23A2 in human embryonic palatal mesenchymal cell line (HEPM) induced decreased intracellular ascorbic acid (AA), increased reactive oxygen species (ROS), inhibited cell proliferation and triggered apoptosis, activated the PI3K-AKT-mTOR signaling pathway and inhibited autophagy; ROS levels and apoptosis ratio significantly decreased when we supplemented AA to HEPM cells with high ROS levels induced by Sin-1 (an exogenous ROS mimic). Knocked down SLC23A2 in HEPM cells or zebrafish, they became more sensitive to Sin-1, and AA supplementation was ineffective. In conclusion, we identified a novel susceptibility gene SLC23A2 for NSCPO, it may function by decreasing AA level, increasing the ROS levels, inducing apoptosis, and inhibiting autophagy through the activation of the PI3K-AKT-mTOR pathway in etiology of cleft palate.