Comparative proteomics reveals elevated CCN2 in NGLY1-deficient cells.

N-glycanase 1(NGLY1) catalyzes the removal of N-linked glycans from newly synthesized or misfolded protein. NGLY1 deficiency is a recently diagnosed rare genetic disorder. The affected individuals present a broad spectrum of clinical features. Recent studies explored several possible molecular mechanisms of NGLY1 deficiency including defects in proteostasis, mitochondrial homeostasis, innate immunity, and water/ion transport. We demonstrate abnormal accumulation of endoplasmic reticulum-associated degradation (ERAD) substrates in NGLY1-deficient cells. Global quantitative proteomics discovered elevated levels of endogenous proteins in NGLY1-defective human and mouse cells. Further biological validation assays confirmed the altered abundance of several key candidates that were subjected to isobarically labeled proteomic analysis. CCN2 was selected for further analysis due to its significant increase in different cell models of NGLY1 deficiency. Functional assays show elevated CCN2 and over-stimulated TGF-β signaling in NGLY1-deficient cells. Given the important role of CCN2 and TGF-β pathway in mediating systemic fibrosis, we propose a potential link of increased CCN2 and TGF-β signaling to microscopic liver fibrosis in NGLY1 patients.