HIF1α is a central regulator of collagen hydroxylation and secretion under hypoxia during bone development

Abstract

Collagen production is fundamental for the ontogeny and the phylogeny of all multicellular organisms. It depends on hydroxylation of proline residues, a reaction that uses molecular oxygen as a substrate. This dependency is expected to limit collagen production to oxygenated cells. However, during embryogenesis, cells in different tissues that develop under low oxygen levels must produce this essential protein. In this study, using the growth plate of developing bones as a model system, we identify the transcription factor hypoxia-inducible factor 1 α (HIF1α) as a central component in a mechanism that underlies collagen hydroxylation and secretion by hypoxic cells. We show that Hif1a loss of function in growth plate chondrocytes arrests the secretion of extracellular matrix proteins, including collagen type II. Reduced collagen hydroxylation and endoplasmic reticulum stress induction in Hif1a-depleted cells suggests that HIF1α regulates collagen secretion by mediating its hydroxylation and consequently its folding. We demonstrate in vivo the ability of Hif1α to drive the transcription of collagen prolyl 4-hydroxylase, which catalyzes collagen hydroxylation. We also show that, concurrently, HIF1α maintains cellular levels of oxygen, most likely by controlling the expression of pyruvate dehydrogenase kinase 1, an inhibitor of the tricarboxylic acid cycle. Through this two-armed mechanism, HIF1α acts as a central regulator of collagen production that allows chondrocytes to maintain their function as professional secretory cells in the hypoxic growth plate. As hypoxic conditions occur also during pathological conditions such as cancer, our findings may promote the understanding not only of embryogenesis, but also of pathological processes.

Functional Consequences of Intracellular Proline Levels Manipulation Affecting PRODH/POX–Dependent Pro-Apoptotic Pathways in a Novel in Vitro Cell Culture Model

“…COX-2, VEGF, TNF-α, IL-1, NF-kB) promote pro-survival signalling pathways [48]. Interestingly, HIF-1α was also found to play a regulatory role in hydroxylation and secretion of collagen [49] suggesting another modulatory mechanism of collagen production. We provided evidence that expression of HIF-1α was more pronounced in MCF-7 shPRODH/POX cells than in MCF-7 cells, suggesting pro-survival mode of the cells.…”

Hypoxia and the extracellular matrix: drivers of tumour metastasis

“…HIF1 regulates the expression of P4HA1, P4HA2, PLOD1 and PLOD2 in cancer cells, fibroblasts, chondrocytes and endothelial cells 20,21,67,82–86 . Abrogating the expression of HIF1α, P4HA1 or P4HA2 through the stable transfection of cells with short hairpin RNA (shRNA) vectors inhibits collagen deposition from both breast cancer cells and fibroblasts in vitro 21,82 .…”

Role of HIF-1α and HIF-2α in osteoarthritis

“…In the cartilage engineering, HIF-1␣ also shows its chondrogenesis capacity; overexpressed HIF-1␣ is effective and sufficient to induce chondrocyte phenotype in human bone marrow cells even without use of exogenous growth factors [26]. HIF-1␣ also acts as a central regulator of collagen production that allows chondrocytes to maintain their function as professional secretory cells in the hypoxic growth plate [27,28]. Hypoxia and HIF-1␣ not only induce the expression of SOX9, COL2A1, and aggrecan [29], but they simultaneously inhibit the expression of COL1A1, COL1A2, and COL3A1 [30].…”