Absence of the ER Cation Channel TMEM38B/TRIC-B Disrupts Intracellular Calcium Homeostasis and Dysregulates Collagen Synthesis in Recessive Osteogenesis Imperfecta
Fig 7
Collagen conformation and secretion are altered by abnormal ER [Ca2+].
(A) Differential scanning calorimetry (DSC) analysis reveals no differences in thermal stability (Tm) of type I collagen secreted by control (C, media) and LH1-deficient (EDS VI, media) fibroblast cultures, but a low-stability fraction in proband (P1, P2, media) secreted collagen. Thermal stability of type I collagen extracted from extracellular matrix deposited in culture by control (C, matrix) and proband (P1, P2, matrix) cells is equivalent. (B) Immunoblots of intracellular (cell) and secreted (media) type I collagen from control (C) or proband (P1, P2) fibroblasts (FB) and osteoblasts (OB, P2) cultured in the absence or presence of proteasomal inhibitor (MG132). Retention of type I collagen in proband cells is increased upon treatment. (C) Quantitation of total procollagens in 24 hour conditioned media of control (C) and proband cell cultures. Secretion of procollagens is decreased by more than one-half in proband fibroblasts (P1, P2, P3) and osteoblasts (P2). **, p < 0.01; ***, p < 0.001.