Suppressing phosphoinositide-specific phospholipases Cγ1 promotes mineralization of osteoarthritic subchondral bone osteoblasts via increasing autophagy, thereby ameliorating articular cartilage degeneration

Non-coding RNAs as regulators of autophagy in chondrocytes: Mechanisms and implications for osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease with multiple causative factors such as aging, mechanical injury, and obesity. Autophagy is a complex dynamic process that is involved in the degradation and modification of intracellular proteins and organelles under different pathophysiological conditions. Autophagy, as a cell survival mechanism under various stress conditions, plays a key role in regulating chondrocyte life cycle metabolism and cellular homeostasis. Non-coding RNAs (ncRNAs) are heterogeneous transcripts that do not possess protein-coding functions, but they can act as effective post-transcriptional and epigenetic regulators of gene and protein expression, thus participating in numerous fundamental biological processes. Increasing evidence suggests that ncRNAs, autophagy, and their crosstalk play crucial roles in OA pathogenesis. Therefore, we summarized the complex role of autophagy in OA chondrocytes and focused on the regulatory role of ncRNAs in OA-associated autophagy to elucidate the complex pathological mechanisms of the ncRNA-autophagy network in the development of OA, thus providing new research targets for the clinical diagnosis and treatment of OA.

Insights into the underlying pathogenesis and therapeutic potential of endoplasmic reticulum stress in degenerative musculoskeletal diseases

Degenerative musculoskeletal diseases are structural and functional failures of the musculoskeletal system, including osteoarthritis, osteoporosis, intervertebral disc degeneration (IVDD), and sarcopenia. As the global population ages, degenerative musculoskeletal diseases are becoming more prevalent. However, the pathogenesis of degenerative musculoskeletal diseases is not fully understood. Previous studies have revealed that endoplasmic reticulum (ER) stress is a stress response that occurs when impairment of the protein folding capacity of the ER leads to the accumulation of misfolded or unfolded proteins in the ER, contributing to degenerative musculoskeletal diseases. By affecting cartilage degeneration, synovitis, meniscal lesion, subchondral bone remodeling of osteoarthritis, bone remodeling and angiogenesis of osteoporosis, nucleus pulposus degeneration, annulus fibrosus rupture, cartilaginous endplate degeneration of IVDD, and sarcopenia, ER stress is involved in the pathogenesis of degenerative musculoskeletal diseases. Preclinical studies have found that regulation of ER stress can delay the progression of multiple degenerative musculoskeletal diseases. These pilot studies provide foundations for further evaluation of the feasibility, efficacy, and safety of ER stress modulators in the treatment of musculoskeletal degenerative diseases in clinical trials. In this review, we have integrated up-to-date research findings of ER stress into the pathogenesis of degenerative musculoskeletal diseases. In a future perspective, we have also discussed possible directions of ER stress in the investigation of degenerative musculoskeletal disease, potential therapeutic strategies for degenerative musculoskeletal diseases using ER stress modulators, as well as underlying challenges and obstacles in bench-to-beside research.

Impaired autophagy contributes to the aggravated deterioration of osteoarthritis articular cartilage by peroxisome proliferator-activated receptor α deficiency, associated with decreased ERK and Akt activation

BACKGROUND

Although the chondroprotection of peroxisome proliferator-activated receptor α (PPARα) activation against osteoarthritis (OA) has been revealed, the regulatory mechanism of PPARα deficiency to aggravate osteoarthritic cartilage deterioration remains unclear. Here, we aimed to investigate whether and how autophagy is involved in OA pathological progression.

METHODS

Model of experimental OA was established using destabilization of the medial meniscus in PPARα-KO 129S4/SvJae male mice, followed by histopathological detection of articular cartilage and immunohistochemistry detection of extracellular matrix (ECM) or autophagy-related signal molecules. Meanwhile, human OA chondrocytes obtained from total knee replacement surgery patients with OA were cultured with the pretreatment of IL-1β, followed with the treatment of PPARα agonist WY14643 and the detection of related signal molecules.

RESULTS

PPARα deficiency aggravated cartilage damage with decreased LC3B level in combination with an increase in P62 level, accompanied with reduced p-Akt and p-ERK levels in PPARα-KO mouse model of experimental OA. On the contrary, PPARα activation by WY14643 promoted ECM synthesis in IL-1β-treated human OA chondrocytes, accompanied with increased LC3B-II/I ratio and Beclin 1 level and decreased P62 and Bcl2 levels. Meanwhile, it was observed that activated ERK and Akt by PPARα activation contributed to the enhancement of autophagy and ECM synthesis in human OA chondrocytes.

CONCLUSIONS

Impaired autophagy contributed to the aggravated deterioration of osteoarthritis articular cartilage by PPARα deficiency associated with the suppression of ERK and Akt, with an implication that triggering PPARα activation ought to be a potential promising therapeutic target for OA therapy.

Structural characterization and anti-osteoporosis effect of an arabinomannan from Anemarrhena asphodeloides Bge

To discover the polysaccharide with anti-diabetic osteoporosis (DOP) activity and clarify its structure, an arabinomannan (PAAP-1B) with a molecular weight of 14.0 kDa was isolated from Anemarrhena asphodeloides Bge. using column chromatography. It consists of arabinose, mannose, and galactose in a molar ratio of 6:3:1. PAAP-1B has a backbone composed of 1,5-α-Araf, 1,4-β-Manp, and 1,6-β-Galp residues that are branched at C3 of α-Araf and β-Galp residues. The side chains are T-α-Araf, T-α-Manp, T-β-Galp, and 1,6-β-Galp. PAAP-1B attenuated DOP and reduced ferroptosis in the femurs and tibias of alloxan-induced mice. It also suppressed ferroptosis in advanced glycation end product-induced osteoblasts by decreasing 4-hydroxynonenal, malondialdehyde, mitochondrial reactive oxidative species levels, and lipid peroxidation, while reversing the downregulation of solute carrier family 7 membrane 11 and glutathione expression.

Endoplasmic Reticulum Stress in Osteoarthritis: A Novel Perspective on the Pathogenesis and Treatment

Osteoarthritis (OA), the most common degenerative joint disease, causes an enormous socioeconomic burden due to its disabling properties and high prevalence. Increasing evidence suggests that OA is a whole-joint disease involving cartilage degradation, synovitis, meniscal lesions, and subchondral bone remodeling. Endoplasmic reticulum (ER) stress is the accumulation of misfolded/unfolded proteins in the ER. Recent studies have found that ER stress is involved in the OA pathological changes by influencing the physiological function and survival of chondrocytes, fibroblast-like synoviocytes, synovial macrophages, meniscus cells, osteoblasts, osteoclasts, osteocytes, and bone marrow mesenchymal stem cells. Therefore, ER stress is an attractive and promising target for OA. However, although targeting ER stress has been proven to alleviate OA progression in vitro and in vivo, the treatments for OA remain in preclinical stage and require further investigation.