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Contrasting Local and Macroscopic Effects of Collagen Hydroxylation.

ABSTRACT: Collagen is heavily hydroxylated. Experiments show that proline hydroxylation is important to triple helix (monomer) stability, fibril assembly, and interaction of fibrils with other molecules. Nevertheless, experiments also show that even without hydroxylation, type I collagen does assemble into its native D-banded fibrillar structure. This raises two questions. Firstly, even though hydroxylation removal marginally affects macroscopic structure, how does such an extensive chemical change, which is expected to substantially reduce hydrogen bonding capacity, affect local structure? Secondly, how does such a chemical perturbation, which is expected to substantially decrease electrostatic attraction between monomers, affect collagen's mechanical properties? To address these issues, we conduct a benchmarked molecular dynamics study of rat type I fibrils in the presence and absence of hydroxylation. Our simulations reproduce the experimental observation that hydroxylation removal has a minimal effect on collagen's D-band length. We also find that the gap-overlap ratio, monomer width and monomer length are minimally affected. Surprisingly, we find that de-hydroxylation also has a minor effect on the fibril's Young's modulus, and elastic stress build up is also accompanied by tightening of triple-helix windings. In terms of local structure, de-hydroxylation does result in a substantial drop (23%) in inter-monomer hydrogen bonding. However, at the same time, the local structures and inter-monomer hydrogen bonding networks of non-hydroxylated amino acids are also affected. It seems that it is this intrinsic plasticity in inter-monomer interactions that preclude fibrils from undergoing any large changes in macroscopic properties. Nevertheless, changes in local structure can be expected to directly impact collagen's interaction with extra-cellular matrix proteins. In general, this study highlights a key challenge in tissue engineering and medicine related to mapping collagen chemistry to macroscopic properties but suggests a path forward to address it using molecular dynamics simulations.

SUBMITTER: Varma S

PROVIDER: S-EPMC8396666 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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.

Project description:IntroductionSalvage radiotherapy is the only curative treatment for biochemical progression after radical prostatectomy. Macroscopic recurrence may be found in the prostatic bed. The purpose of our study is to evaluate the effectiveness of salvage radiotherapy of the prostate bed with a boost to the area of the macroscopic recurrence.Material and methodsFrom January 2005 to January 2020, 89 patients with macroscopic recurrence in the prostatectomy bed were treated with salvage radiotherapy +/- hormone therapy. The average PSA level prior to radiotherapy was 1.1 ng/mL (SD: 1.6). At the time of biochemical progression, 96% of the patients had a MRI that revealed the macroscopic recurrence, and 58% had an additional choline PET scan. 67.4% of the patients got a boost to the macroscopic nodule, while 32.5% of the patients only underwent radiotherapy of the prostate bed without a boost. The median total dose of radiotherapy was 70 Gy (Min.: 60 - Max.: 74). The most commonly-used regimen was radiotherapy of the prostatectomy bed with a concomitant boost. 48% of the patients were concomitantly treated with hormone therapy.ResultsAfter a median follow-up of 53.7 months, 77 patients were alive and 12 had died, of which 4 following metastatic progression. The 5-year and 8-year survival rates (CI95%) are, respectively, 90.2% (78.9-95.6%) and 69.8% (46.4-84.4%). The 5-year biochemical progression-free survival rate (CI95%) is 50.8% (36.7-63.3). Metastatic recurrence occurred in 11.2% of the patients. We did not find any statistically significant impact from the various known prognostic factors for biochemical progression-free survival. No toxicity with a grade of > or = to 3 was found.ConclusionsOur series is one of the largest published to date. Salvage radiotherapy has its place in the management of patients with biochemical progression with local recurrence in the prostate bed, with an acceptable toxicity profile. The interest of the boost is to be evaluated in prospective trials.

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Contrasting Local and Macroscopic Effects of Collagen Hydroxylation.

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