Proteomic alterations in patient bone-derived stromal cells and their secretomes in osteogenesis imperfecta.

Type I collagen is the most abundant form of collagen and forms the organic component of bone. Pathogenic variants in genes encoding its constituent polypeptide chains, COL1A1 and COL1A2, can result in autosomal dominant osteogenesis imperfecta and other connective tissue disorders. Although osteogenesis imperfecta is clinically well-described, the molecular basis of clinical heterogeneity among patients is not well understood. We undertook a global proteomic approach to uncover alterations in osteogenesis imperfecta patient bone-derived stromal cells as well as their secretome. We performed multiplexed tandem mass tag (TMT)-based proteomics analysis of cells from three patients along with three controls to investigate global changes in the proteome of these cells as well as their secretome. This was combined with analysis of proline hydroxylation to catalog the modification of type I collagens in this disorder. We observed significant changes in both the cellular and secreted proteomes including the levels of proteins involved in osteoblast proliferation such as nitric oxide synthase-interacting protein (NOSIP), secreted frizzled-related protein 1 (SRFP1) and transforming growth factor beta-1-induced transcript 1 protein (TGFB1I1) as well as others involved in endoplasmic reticulum homeostasis such as protein disulfide isomerase A6 (PDIA6) and reticulophagy regulator 3 (RETREG3). Notably, a number of alterations were observed in proline hydroxylation in intracellular collagens - COL1A1 and COL1A2. These findings expand our current understanding of the cellular pathophysiology in osteogenesis imperfecta and could lead to the identification of novel therapeutic targets.