Impaired collagen deposition in the absence of ERp44

The biogenesis of secretory proteins proceeds under sequential quality control checkpoints operating along the exocytic pathway. Unlike other chaperones that reside primarily in the endoplasmic reticulum, ERp44 cycles through the Golgi to control the assembly of polymeric proteins and the localization of a few endoplasmic reticulum resident enzymes (ERAP1, Prx4, Ero1α, and SUMF1). To gain information about its pathophysiological role, we generated ERp44-deficient models. ERp44 KO mice are smaller than control siblings, and show skeletal malformations and delayed bone development, with reduced collagen deposition. Similar skeletal defects were also observed in ERp44 knocked down zebrafish embryos, supporting a conserved role for ERp44 in skeletal development. In cellular models, ERp44 downregulation dramatically affects collagen type 1 deposition, causing intracellular procollagen 1 accumulation. We thus conclude that the levels of ERp44 are crucial for efficient collagen deposition.