Vascular structure and function in the medial collateral ligament of anterior cruciate ligament transected rabbit knees

Abstract

To determine if decreased vascular responsiveness in the medial collateral ligament (MCL) of anterior cruciate ligament transected (ACL-t) rabbit knees is due to pericyte deficiency associated with angiogenesis. Vascular responses to potassium chloride (KCl), phenylephrine, acetylcholine, and sodium nitroprusside (SNP) were evaluated in ACL-t rabbit knees (n ¼ 6) and control knees (n ¼ 5) using laser speckle perfusion imaging. Ligament degeneration was determined by ultrasound imaging. Vascular and pericyte volume were measured using quantitative immunohistochemical volumetric analysis using CD31 and a-smooth muscle actin antibodies with co-localization analysis. Perfusion was increased in the ACL-t rabbits 2.5-fold. Responsiveness to phenylephrine, SNP, and acetylcholine was significantly decreased in the ACL knee while no change in KCl responses was seen. MCL ultrasound imaging revealed decreased collagen organization, increased ligament thickness, and increased water content in the ACL-t MCL. Vascular Volume was increased fourfold in ACL deficient knees, while pericyte volume to endothelial volume was not changed. No difference in CD31 and a-SMA co-localization was found. Blood vessels in the MCL of ACL-t knees do not lack smooth muscle. [2]. Our focus has centered on the pathologic changes that occur in the MCL following rupture of the anterior cruciate ligament. Our hope is that understanding early secondary OA pathology future interventions may be developed to preserve joint function and improve outcomes.The rabbit ACL transected (ACL-t) model has been extensively tested and is well known model of secondary OA having a reliable and reproducible natural history [3]. Joint instability induces osteoarthritic degeneration of rabbit knees, whereas immediate ACL reconstruction prevents joint degeneration [7]. The MCL tensile strength decreases after ACL-t, exacerbating joint instability [7]. A strong angiogenic response occurs in the MCL following ACL-t [8].The MCL vasculature does not respond appropriately to vasoactive mediators such as phenylephrine (PHE) and acetylcholine (ACH) after ACL-t [9,10].These processes are known as endothelial dysfunctionloss of vasodilatory responses mediated through the endothelium; and vascular dysfunction-loss of vasocontractile responses mediated through smooth muscle. Typically endothelial and vascular dysfunction are associated with inflammation [11]. Alternatively, angiogenesis may lead to decreased vascular smooth muscle and therefore decreased dilatory and contractile responses as has been found in synovium of rheumatoid arthritis patients [12].Quantification of the a-smooth muscle actin (a-SMA) content can be utilized to determine the anatomic state of blood vessels and if these vessels are capable of vasoregulation. 1 A volume based ratiometric analysis of the endothelial volume (CD31 label) to a-SMA content has been previously utilized to determine the composition of angiogenic vessels, 2,3 and using similar methods will define the vascular anatomy of the MC...

Comparative histomorphometric analysis of cellular phenotype in canine stifle ligaments and tendon

“…Reports of previous experimental studies have described findings similar to this study . Medial collateral ligament fibroblasts were predominately fusiform, whereas ACL cells were predominately ovoid and did not resemble typical fibroblasts.…”

“…Despite extensive efforts to understand the pathogenesis of CrCL disease, the exact cause of this common problem is still unknown. Ligaments and tendons are dense regular collagenous connective tissues that share numerous common histological and mechanical properties . The natural course of ligament/tendon healing is similar to other vascular soft tissues.…”

“…The natural course of ligament/tendon healing is similar to other vascular soft tissues. However, in man, it is well documented that the healing responses of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) are dramatically different, ranging from spontaneous healing of the MCL to little or no healing of the ACL . Anterior cruciate ligament and MCL tissues have different biochemical compositions, lie within different synovial environments, have different blood supplies, and experience different magnitude and directions of forces.…”

“…Fibroblasts are the predominant cell types in ligaments and tendons . Fibroblasts are responsible for synthesis of extracellular matrix collagen, which provides ligaments and tendons with mechanical properties required for their functions . In human ACL, 3 distinct fibroblast cell phenotypes (fusiform, ovoid, and spheroid) are defined according to morphology with respect to their nuclear aspect ratio .…”

HMGB1‐induced angiogenesis in perforated disc cells of human temporomandibular joint

“…TMJ disc, a fibro-cartilaginous tissue, aids in joint motions by lubricating the surfaces of motion, decreasing incongruence between the articulating surfaces, and dissipating loads and impact within the joint [20]. A variety of studies have shown that angiogenesis of pathological discs correlates with the severity of joint degeneration [21][22][23]. Our previous study demonstrated the abundance of HMGB1 surrounding the perforated area of discs.…”