Dysregulation of Prolyl Hydroxylation in Human Skeletal Dysplasias and Recessive Osteogenesis Imperfecta
A poorly understood collagen post-translational modification has been 3-prolyl-hydroxylation (P3H) converting proline to 3-hydroxy proline (3-Hyp). It occurs in the fibrillar collagens, i.e., types I, II and III collagen, at only one proline position, but abundantly in other collagens such as network collagens, i.e., type IV collagen, where it occurs in up to 10% of residues. This begs the question of whether 3-Hyp residues serve divergent biological functions in different settings and tissues.
In recent data, we have identified a novel protein, CRTAP or Cartilage Associated Protein, that is representative of the Leprecan family of proteins recently reported to contain a conserved 2-oxoglutarate dioxygenase domain that is found in collagen 4-prolyl-hydroxylases (P4Hs), Hypoxic Inducible Factor (HIF) 4-prolyl- hydoxylases (PDHs), and lysyl hydroxylases (PLODs). Moreover, Leprecan or P3H1 has collagen 3- prolyl-hydroxylase activity in vitro implicating this family of genes as the long sought after P3H's. By combining human and mouse genetic, and proteomic approaches, we have shown that loss of Crtap in mice causes an osteochondrodysplasia characterized by short stature, kyphosis, and severe osteoporosis. Moreover, this phenotype is biochemically associated with conversion of the single 3-hydroxy-proline to proline in the triple helical domain of types I and II collagen. CRTAP can bind P3H1 and is required for P3H activity in vivo .
These data raise important mechanistic questions that we will address in our Specific Aims.
- Are the phenotypic features of Crtap loss of function due solely to loss of 3-prolyl-hydroxylation of fibrillar collagens?
- What are the consequences of 3-Hyp loss in cartilage and bone on cellular differentiation and function, and collagen biosynthesis?
- What is the human clinical spectrum associated with loss of 3-prolyl- hydroxylation of fibrillar collagens?
- What regulates the context-dependent function of CRTAP?
These questions address what we believe to be a new area in matrix biology and pathogenesis of skeletal dysplasias, i.e., the in vivo phenotypic and biochemical consequences of dysregulation of the 3-prolyl-hydroxylation machinery?
Relevance of the project to IDDRC mission:
Dysregulation of prolyl-3 hydroxylation is a novel mechanism for human connective tissue disease. Among them include the brittle bone disorders such as osteogenesis imperfecta. They constitute a group of disorders associated with significant physical disability related to immobility, fracture, and pain. Moreover, patients are neurodevelopmentally intact. Hence, developing accurate diagnostic and interventional approaches are important in decreasing morbidity associated with these conditions.