Transcription Factor Mohawk and the Pathogenesis of Human Anterior Cruciate Ligament Degradation

Abstract

Objective To investigate the expression and function of Mohawk (MKX) in human adult anterior cruciate ligament (ACL) tissues and ligament cells from normal and osteoarthritis-affected knees. Methods Knee joints were obtained at autopsy within 24-48 hours postmortem from 13 normal donors (age 36.9±11.0 years), 16 OA donors (age 79.7±11.4 years) and 8 old donors without OA (age 76.9±12.9 years). All cartilage surfaces were graded macroscopically. MKX expression was analyzed by immunohistochemistry and quantitative PCR. ACL-derived cells were used to study regulation of MKX expression by IL-1β. MKX was knocked down by siRNA to analyze function of MKX in extracellular matrix (ECM) production and differentiation in ACL-derived cells. Results The expression of MKX was significantly decreased in ACL-derived cells from OA knees compared with normal knees. Consistent with this finding, immunohistochemistry showed that MKX positive cells were significantly reduced in ACL tissues from OA donors in particular in cells located in disorientated fibers. In ACL-derived cells, IL-1β strongly suppressed MKX gene expression and reduced ligament ECM genes, COL1A1 and TNXB. On the other hand, SOX9, chondrocyte master transcription factor, was up regulated by IL-1β treatment. Importantly, knock down of MKX expression by siRNA upregulated SOX9 expression in ACL-derived cells, whereas the expression of COL1A1 and TNXB were decreased. Conclusion Reduced expression of MKX is a feature of degenerated ACL in OA-affected joints and this may be in part mediated by IL-1β. MKX appears necessary to maintain the tissue specific cellular differentiation status and ECM production in adult human tendons and ligaments.

Mohawk transcription factor regulates homeostasis of the periodontal ligament

“…Additionally, it is known that the PDL in periapical periodontitis is excessively expanded with the accumulation of inflammatory cells (Page and Schroeder, 1976). We previously observed that Mkx expression in human tendon cells is downregulated by inflammatory signals such as IL-1β stimulation (Nakahara et al, 2013). Inflammatory markers were not elevated in Mkx −/− mice, suggesting that PDL degeneration is due to changes in the expression of PDL-and osteogenic-related genes rather than inflammation (Fig.…”

“…In elderly subjects, the PDL shows atrophic changes and loss of function (Sloan, 1995). We reported that MKX expression in human tendon cells is reduced with age, indicating a function of MKX in tendon homeostasis (Nakahara et al, 2013). In this regard, the detailed analysis of potential Mkx expression changes with age, both in humans and mice, may lead us to uncover new information about the pathogenesis of PDL-related diseases.…”

The Mohawk homeobox transcription factor regulates the differentiation of tendons and volar plates

“…These data suggest that this morphologic difference might be due to mechanical stress or degenerative changes after birth. In this regard, we recently reported the potential role of Mkx in human tendon/ligament tissue homeostasis 28 . Since Mkx expression in VPs and pulleys was observed in adult mice, Mkx may also be involved in VP and pulley homeostasis and regeneration.…”

Tendons and Ligaments: Connecting Developmental Biology to Musculoskeletal Disease Pathogenesis

“…The numbers of ligament cells expressing MKX are reduced in OA ACL. HE staining ( A , C ) and MKX immunohistochemistry ( B , D ) (modified from Nakahara and colleagues).…”

“…As described above, the expression of Mkx is reduced in human ACL from aged and OA‐affected knees. One potential mechanism behind the suppression of Mkx is the involvement of inflammatory cytokines, such as IL‐1 . Thus, the loss of Mkx, driven by proinflammatory cytokines such as IL‐1β, can lead to the abnormal chondrocyte‐like differentiation of ligament cells and a reduced production of ECM with deficient biomechanical properties.…”