The effect of collagen organization on tensile strength loss in anterior cruciate ligament grafts post-reconstruction surgery

Gemstone Team LEGSGrafts used for anterior cruciate ligament (ACL) reconstructions fall short of restoring native mechanics. This study investigated a morphological cause for tension loss by comparing native ACL and two common grafts, bone-patellar tendonbone (BPTB) and semitendinosus/gracilis hamstring tendon (ST/G), in a cadaveric system. Tension loss during continuous passive motion was quantified via force transducer. Microstructural changes were assessed by measuring collagen crimp angles. No significant differences were found for rates of percent tension loss relative to total tension loss among grafts. However, all groups displayed exponential decay, implying rapid tension loss. The crimp angles for the unstressed grafts were significantly different from each other, suggesting innate differences. The percent change experienced by stressed grafts, normalized to their unstressed baselines, showed that ST’s crimp behavior was significantly different from that of ACL and BPTB, implying the BPTB graft is superior for ACL reconstruction because it better mimics the ACL’s morphological behavior

Provisional extracellular matrix citrullination as a stimulus for pathological fibroblast activation

Activated fibroblasts have been implicated as drivers of disease progression in a variety of conditions including rheumatoid arthritis (RA), fibrotic diseases, and cancer, and importantly, there currently exists a dearth of understanding regarding how fibroblasts become activated. The central hypothesis of this work is that an inflammation-mediated provisional extracellular matrix (pECM) modification called citrullination may be responsible in whole or in part for activated fibroblast phenotypes. In Aim 1 the influence of citrullinated fibronectin (Cit Fn) was investigated at a molecular scale utilizing a combination of mass spectrometry (MS), bio-layer interferometry (BLI), and immunocytochemistry (ICC) and force-inducible co-immunoprecipitation methods to probe for integrin interactions and downstream signaling. A total of 24 unique citrullination sites were discovered that effectively cause a shift in integrin preference from αvβ3 towards α5β1 that ultimately leads to enhancement of mechanotransduction signaling. In Aim 2 the ability of citrullinated pECM (Cit-pECM) as a stand-alone stimulus to influence fibroblast behavior was explored through a variety of adhesion, migration, apoptosis, proliferation, contraction, and focal adhesion (FA) turnover assays, in addition to atomic force microscopy (AFM). Results indicate that Cit-pECM is sufficient to impact several aspects of fibroblast behavior including increasing FA turnover which leads to an enhancement of cell migration. Overall these findings signify that Cit-pECM is influential in the context fibroblast activation and it may therefore constitute a promising therapeutic target in the treatment of a variety of inflammatory conditions.Ph.D