Differential effects of collagen prolyl 3-hydroxylation on skeletal tissues.
Mutations in the genes encoding cartilage associated protein (CRTAP) and prolyl 3-hydroxylase 1 (P3H1 encoded by LEPRE1) were the first identified causes of recessive Osteogenesis Imperfecta (OI). These proteins, together with cyclophilin B (encoded by PPIB), form a complex that 3-hydroxylates a single proline residue on the α1(I) chain (Pro986) and has cis/trans isomerase (PPIase) activity essential for proper collagen folding. Recent data suggest that prolyl 3-hydroxylation of Pro986 is not required for the structural stability of collagen; however, the absence of this post-translational modification may disrupt protein-protein interactions integral for proper collagen folding and lead to collagen over-modification. P3H1 and CRTAP stabilize each other and absence of one results in degradation of the other. Hence, hypomorphic or loss of function mutations of either gene cause loss of the whole complex and its associated functions. The relative contribution of losing this complex's 3-hydroxylation versus PPIase and collagen chaperone activities to the phenotype of recessive OI is unknown. To distinguish between these functions, we generated knock-in mice carrying a single amino acid substitution in the catalytic site of P3h1 (Lepre1(H662A) ). This substitution abolished P3h1 activity but retained ability to form a complex with Crtap and thus the collagen chaperone function. Knock-in mice showed absence of prolyl 3-hydroxylation at Pro986 of the α1(I) and α1(II) collagen chains but no significant over-modification at other collagen residues. They were normal in appearance, had no growth defects and normal cartilage growth plate histology but showed decreased trabecular bone mass. This new mouse model recapitulates elements of the bone phenotype of OI but not the cartilage and growth phenotypes caused by loss of the prolyl 3-hydroxylation complex. Our observations suggest differential tissue consequences due to selective inactivation of P3H1 hydroxylase activity versus complete ablation of the prolyl 3-hydroxylation complex.
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Erica P
EP
Homan
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Caressa
C
Lietman
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Ingo
I
Grafe
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Jennifer
J
Lennington
Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
Roy
R
Morello
Department of Oral and Maxillofacial Surgery, School of Dentistry, University of Alabama at Birmingham, Birmingham, Alabama, United States of America.
Dobrawa
D
Napierala
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America ; Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America.
Ming-Ming
MM
Jiang
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Elda M
EM
Munivez
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America ; Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America.
Brian
B
Dawson
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Terry K
TK
Bertin
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America ; Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America.
Yuqing
Y
Chen
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Rhonald
R
Lua
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
Olivier
O
Lichtarge
Department of Pathology, Texas Children's Hospital, Baylor College of Medicine, Houston, Texas, United States of America.
John
J
Hicks
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
Mary Ann
MA
Weis
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
David
D
Eyre
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America ; Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America.
Brendan H L
BH
Lee
D000818:Animals; D003094:Collagen / Q000737:chemistry / Q000235:genetics*; D021983:Cyclophilins / Q000235:genetics; D016326:Extracellular Matrix Proteins; D055879:Gene Knock-In Techniques; D006900:Hydroxylation / Q000235:genetics*; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones; D010012:Osteogenesis / Q000235:genetics*; D010013:Osteogenesis Imperfecta / Q000235:genetics* / Q000473:pathology; D017510:Protein Folding; D060066:Protein Interaction Maps; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D011509:Proteoglycans / Q000235:genetics* / Q000378:metabolism; D012863:Skeleton
C486354:Crtap protein, mouse; D016326:Extracellular Matrix Proteins; C485658:Lepre1 protein, mouse; D008562:Membrane Glycoproteins; D018832:Molecular Chaperones; D011506:Proteins; D011509:Proteoglycans; C081786:cyclophilin B; D003094:Collagen; D021983:Cyclophilins