Bone Research最新文献

Intervertebral disc degeneration (IVDD) is the primary contributor to a range of spinal diseases. Dynamin-related protein 1 (Drp1)-mediated mitochondrial fission has recently been identified as a new cause of nucleus pulposus cell (NPC) death and IVDD, but the underlying mechanisms remain unclear. Although the effects of Drp1 phosphorylation in IVDD have been studied, it is currently unknown if small ubiquitin-like modifications (SUMOylation) of Drp1 regulate IVDD. This study aimed to investigate the functions and mechanisms of mitochondria-anchored protein ligase (MAPL), a mitochondrial SUMO E3 ligase, during IVDD progression. The expression of genes related to SUMOylation and mitochondrial dynamics in TNF-α-stimulated NPCs was analysed via RNA sequencing. The levels of total and mitochondrial SUMO1 conjugates were elevated with MAPL upregulation in TNF-α-treated NPCs. Additionally, mitochondrial fragmentation and dysfunction were induced by TNF-α stimulation. MAPL overexpression promoted mitochondrial SUMOylation and SUMO1 modification of Drp1, thereby facilitating the mitochondrial translocation of Drp1 and mitochondrial fission. MAPL-induced ROS accumulation and ΔΨm loss led to increased NPC apoptosis. Mutation of the SUMO-acceptor lysine residues of Drp1 hindered its SUMOylation and rescued the mitochondrial phenotypes caused by MAPL. SENP5 overexpression phenocopied MAPL silencing, negatively modulating the SUMO1 modification of Drp1 and mitochondrial fission in NPCs. In a rat IVDD model, forced expression of MAPL by using an adeno-associated virus (AAV) vector aggravated IVD tissue damage, whereas the knockdown of MAPL delayed IVDD progression. Our findings highlight the importance of SUMOylation in IVDD. The inhibition of MAPL-mediated Drp1 SUMOylation alleviates mitochondrial fission and limits IVDD development, providing a potential strategy for IVDD treatment.

Precision medicine has become a cornerstone in modern therapeutic strategies, with nucleic acid aptamers emerging as pivotal tools due to their unique properties. These oligonucleotide fragments, selected through the Systematic Evolution of Ligands by Exponential Enrichment process, exhibit high affinity and specificity toward their targets, such as DNA, RNA, proteins, and other biomolecules. Nucleic acid aptamers offer significant advantages over traditional therapeutic agents, including superior biological stability, minimal immunogenicity, and the capacity for universal chemical modifications that enhance their in vivo performance and targeting precision. In the realm of osseous tissue repair and regeneration, a complex physiological process essential for maintaining skeletal integrity, aptamers have shown remarkable potential in influencing molecular pathways crucial for bone regeneration, promoting osteogenic differentiation and supporting osteoblast survival. By engineering aptamers to regulate inflammatory responses and facilitate the proliferation and differentiation of fibroblasts, these oligonucleotides can be integrated into advanced drug delivery systems, significantly improving bone repair efficacy while minimizing adverse effects. Aptamer-mediated strategies, including the use of siRNA and miRNA mimics or inhibitors, have shown efficacy in enhancing bone mass and microstructure. These approaches hold transformative potential for treating a range of orthopedic conditions like osteoporosis, osteosarcoma, and osteoarthritis. This review synthesizes the molecular mechanisms and biological roles of aptamers in orthopedic diseases, emphasizing their potential to drive innovative and effective therapeutic interventions.

Cellular senescence and its senescence-associated secretory phenotype (SASP) represent a pivotal role in the development of skeletal diseases. Targeted elimination or rejuvenation of senescent cells has shown potential as a therapeutic strategy to reverse age-related skeletal senescence and promote bone regeneration. Meanwhile, other age-related mechanisms, involving altered cellular functions, impaired intercellular crosstalk, disturbed tissue microenvironment, and decreased regenerative capacity, synergistically contribute to the pathogenesis. In this review, we outline the cellular senescence and other age-related mechanisms in developing skeletal diseases, including osteoporosis, intervertebral disc degeneration, osteoarthritis, rheumatoid arthritis, bone tumors and ankylosing spondylitis, with the aim of comprehensively understanding their detrimental effects on the aged skeleton and screening the potential targets for anti-aging therapy within the skeletal system.

Polytrauma with significant bone and volumetric muscle loss presents substantial clinical challenges. Although immune responses significantly influence fracture healing post-polytrauma, the cellular and molecular underpinnings of polytrauma-induced immune dysregulation require further investigation. While previous studies examined either injury site tissue or systemic tissue (peripheral blood), our study uniquely investigated both systemic and local immune cells at the same time to better understand polytrauma-induced immune dysregulation and associated impaired bone healing. Using single-cell RNA sequencing (scRNA-seq) in a rat polytrauma model, we analyzed blood, bone marrow, and the local defect soft tissue to identify potential cellular and molecular targets involved in immune dysregulation. We identified a trauma-associated immunosuppressive myeloid (TIM) cell population that drives systemic immune dysregulation, immunosuppression, and potentially impaired bone healing. We found CD1d as a global marker for TIM cells in polytrauma. In the local defect tissue, we observed Spp1⁺ monocytes/macrophages mediating inflammatory, fibrotic, and impaired adaptive immune responses. Finally, our findings highlighted increased signaling via Anxa1-Fpr2 and Spp1-Cd44 axes. This comprehensive analysis enhances our understanding of immune dysregulation-mediated nonunion following traumatic injury and provides biomarkers that could function as treatment targets.

Peripheral neuropathy is a common complication in diabetes, affecting around 50% of the diabetic population. Co-occurrence of diabetic peripheral neuropathy (DPN) and diabetic bone disease has led to the hypothesis that DPN influences bone metabolism, although little experimental evidence has yet supported this premise. To investigate, mice were fed a high-fat diet (HFD) followed by phenotyping of skeletal-innervating neurons and bone architectural parameters. Results showed that HFD feeding resulted in a marked decrease in skeletal innervation (69%-41% reduction in Beta-III-Tubulin-stained nerves, 38% reduction in CGRP-stained nerves in long bone periosteum). These changes in skeletal innervation were associated with significant alterations in bone mass and in cortical and trabecular bone microarchitecture of long bones. Single-cell RNA sequencing (scRNA-Seq) of sensory neurons and bone tissue was next utilized to reconstruct potential nerve-to-bone signaling interactions, including implication of sensory nerve-derived neurotrophins (Bdnf), neuropeptides (Gal, Calca and Calcb), and other morphogens (Vegfa, Pdgfa, and Angpt2). Moreover, scRNA-Seq identified marked shifts in periosteal cell transcriptional changes within HFD-fed conditions, including a reduction in cell proliferation, an increase in adipogenic differentiation markers, and reductions in WNT, TGFβ, and MAPK signaling activity. When isolated, periosteal cells from HFD-fed mice showed deficits in proliferative and osteogenic differentiation potential. Moreover, these cellular changes in proliferation and differentiation capacity were restored by treatment of HFD-exposed periosteal cells to sensory neuron-conditioned medium. In summary, HFD modeling of type 2 diabetes results in skeletal polyneuropathy. Moreover, the combination of multi-tissue scRNA-Seq and isolated in vitro studies strengthen the case for altered nerve-to-bone signaling in diabetic bone disease.

The effectiveness of cranial suture expansion therapy hinges on the timely and adequate regeneration of bone tissue in response to mechanical stimuli. To optimize clinical outcomes and prevent post-expansion relapse, we delved into the underlying mechanisms governing bone remodeling during the processes of suture expansion and relapse. Our findings revealed that in vitro stretching bolstered mesenchymal stem cells’ antioxidative and osteogenic capacity by orchestrating mitochondrial activities, which governed by force-induced endoplasmic reticulum (ER) stress. Nonetheless, this signal transduction occurred through the activation of protein kinase R-like ER kinase (PERK) at the ER-mitochondria interface, rather than ER-mitochondria calcium flow as previously reported. Subsequently, PERK activation triggered TFEB translocation to the nucleus, thus regulating mitochondrial dynamics transcriptionally. Assessment of the mitochondrial pool during expansion and relapse unveiled a sequential, two-phase regulation governed by the ER stress/p-PERK/TFEB signaling cascade. Initially, PERK activation facilitated TFEB nuclear localization, stimulating mitochondrial biogenesis through PGC1-α, thereby addressing energy demands during the initial phase. Subsequently, TFEB shifted focus towards ensuring adequate mitophagy for mitochondrial quality maintenance during the remodeling process. Premature withdrawal of expanding force disrupted this sequential regulation, leading to compromised mitophagy and the accumulation of dysfunctional mitochondria, culminating in suboptimal bone regeneration and relapse. Notably, pharmacological activation of mitophagy effectively mitigated relapse and attenuated bone loss, while its inhibition impeded anticipated bone growth in remodeling progress. Conclusively, we elucidated the ER stress/p-PERK/TFEB signaling orchestrated sequential mitochondria biogenesis and mitophagy under mechanical stretch, thus ensuring antioxidative capacity and osteogenic potential of cranial suture tissues.

Membrane-initiated estrogen receptor α (mERα) signaling has been shown to affect bone mass in murine models. However, it remains unknown which cell types mediate the mERα-dependent effects on bone. In this study, we generated a novel mouse model with a conditional C451A mutation in Esr1, which enables selective knockout of the palmitoylation site essential for the membrane localization of ERα (C451A^f/f). First, we used Runx2-Cre mice to generate Runx2-C451A^f/f mice with conditional inactivation of mERα signaling in Runx2-expressing osteoblast lineage cells. No significant changes were observed in body weight, weights of estrogen-responsive organs, or serum concentrations of estradiol between female Runx2-C451A^f/f and homozygous C451A^f/f littermate controls. High-resolution microcomputed tomography analysis showed a consistent decrease in cortical bone mass in the tibia, femur, and vertebra L5 of Runx2-C451A^f/f mice and three-point bending analysis of humerus revealed an impaired mechanical bone strength in Runx2-C451A^f/f female mice compared to controls. Additionally, primary osteoblast cultures from mice lacking mERα signaling showed impaired differentiation compared to controls. In contrast, conditional inactivation of mERα signaling in hematopoietic cells, by transplantation of bone marrow from mice lacking mERα signaling in all cells to adult wildtype female mice, did not result in any skeletal alterations. In conclusion, this study demonstrates that mERα signaling in osteoblast lineage cells plays a crucial role in the regulation of cortical bone in female mice and shows that mERα inactivation in hematopoietic cells of adult female mice is dispensable for bone regulation.

Rheumatoid arthritis (RA) is a prevalent and debilitating inflammatory disease that significantly impairs functional capacity and quality of life. RA accelerates musculoskeletal aging, leading to complications such as muscle degeneration and sarcopenia. Recent research has identified myopenia as a condition of significant muscle loss associated with illness, distinct from the muscle wasting seen in other chronic diseases like cancer cachexia or heart failure. In RA, myopenia is characterized by muscle depletion without concurrent significant fat loss, and it can affect individuals of all ages. While inflammation plays a central role, it is not the sole factor contributing to the high incidence of muscle wasting in RA. In subsequent discussions, secondary sarcopenia will be considered alongside myopenia, as both involve muscle wasting decline primarily due to disease. This review summarizes recent findings on the impact of RA-related myopenia and secondary sarcopenia on functional capacity, explores its underlying mechanisms, and discusses contemporary strategies to mitigate the process of musculoskeletal aging in RA patients.