Bach1 deficiency reduces severity of osteoarthritis through upregulation of heme oxygenase-1

Introduction: BTB and CNC homology 1 (Bach1) is a transcriptional repressor of Heme oxygenase-1 (HO-1), which is cytoprotective through its antioxidant effects. The objective of this study was to define the role of Bach1 in cartilage homeostasis and osteoarthritis (OA) development using in vitro models and Bach1(-/-) mice. Methods: HO-1 expression in Bach1(-/-) mice was analyzed by real-time PCR, immunohistochemistry and immunoblotting. Knee joints from Bach1(-/-) and wild-type mice with age-related OA and surgically-induced OA were evaluated by OA scoring systems. Levels of autophagy proteins and superoxide dismutase 2 (SOD2) were determined by immunohistochemistry. The relationship between HO-1 and the protective effects for OA was determined in chondrocytes treated with small interfering RNA (siRNA) targeting HO-1 gene. Results: HO-1 expression decreased with aging in articular cartilages and menisci of mouse knees. Bach1(-/-) mice showed reduced severity of age-related OA and surgically-induced OA compared with wild-type mice. Microtubule-associated protein 1 light chain 3 (LC3), autophagy marker, and SOD2 were increased in articular cartilage of Bach1(-/-) mice compared with wild-type mice. Interleukin-1 beta (IL-1 beta) induced a significant increase in Adamts-5 in wild-type chondrocytes but not in Bach1(-/-) chondrocytes. The expression of SOD2 and the suppression of apoptosis in Bach1(-/-) chondrocytes were mediated by HO-1. Conclusions: Bach1 deficiency reduces the severity of OA-like changes. This may be due to maintenance of cartilage homeostasis and joint health by antioxidant effects through HO-1 and downregulation of extracellular matrix degrading enzymes. These results suggest that inactivation of Bach1 is a novel target and signaling pathway in OA prevention.