MiR-21-5p regulates the dynamic of mitochondria network and rejuvenates the senile phenotype of bone marrow stromal cells (BMSCs) isolated from osteoporotic SAM/P6 mice

Cell life-or-death events in osteoporosis: All roads lead to mitochondrial dynamics

Mitochondria exhibit heterogeneous shapes and networks within and among cell types and tissues, also in normal or osteoporotic bone tissues with complex cell types. This dynamic characteristic is determined by the high plasticity provided by mitochondrial dynamics and is stemmed from responding to the survival and functional requirements of various bone cells in a specific microenvironments. In contrast, mitochondrial dysfunction, induced by dysregulation of mitochondrial dynamics, may act as a trigger of cell death signals, including common apoptosis and other forms of programmed cell death (PCD). These PCD processes consisting of tightly structured cascade gene expression events, can further influence the bone remodeling by facilitating the death of various bone cells. Mitochondrial dynamics, therefore, drive the bone cells to stand at the crossroads of life and death by integrating external signals and altering metabolism, shape, and signal-response properties of mitochondria. This implies that targeting mitochondrial dynamics displays significant potential in treatment of osteoporosis. Considerable effort has been made in osteoporosis to emphasize the parallel roles of mitochondria in regulating energy metabolism, calcium signal transduction, oxidative stress, inflammation, and cell death. However, the emerging field of mitochondrial dynamics-related PCD is not well understood. Herein, to bridge the gap, we outline the latest knowledge on mitochondrial dynamics regulating bone cell life or death during normal bone remodeling and osteoporosis.

DNA Tetrahedron Delivering miR-21-5p Promotes Senescent Bone Defects Repair through Synergistic Regulation of Osteogenesis and Angiogenesis

Compromised osteogenesis and angiogenesis is the character of stem cell senescence, which brought difficulties for bone defects repairing in senescent microenvironment. As the most abundant bone-related miRNA, miRNA-21-5p plays a crucial role in inducing osteogenic and angiogenic differentiation. However, highly efficient miR-21-5p delivery still confronts challenges including poor cellular uptake and easy degradation. Herein, TDN-miR-21-5p nanocomplex is constructed based on DNA tetrahedral (TDN) and has great potential in promoting osteogenesis and alleviating senescence of senescent bone marrow stem cells (O-BMSCs), simultaneously enhancing angiogenic capacity of senescent endothelial progenitor cells (O-EPCs). Of note, the activation of AKT and Erk signaling pathway may direct regulatory mechanism of TDN-miR-21-5p mediated osteogenesis and senescence of O-BMSCs. Also, TDN-miR-21-5p can indirectly mediate osteogenesis and senescence of O-BMSCs through pro-angiogenic growth factors secreted from O-EPCs. In addition, gelatin methacryloyl (GelMA) hydrogels are mixed with TDN and TDN-miR-21-5p to fabricate delivery scaffolds. TDN-miR-21-5p@GelMA scaffold exhibits greater bone repair with increased expression of osteogenic- and angiogenic-related markers in senescent critical-size cranial defects in vivo. Collectively, TDN-miR-21-5p can alleviate senescence and induce osteogenesis and angiogenesis in senescent microenvironment, which provides a novel candidate strategy for senescent bone repair and widen clinical application of TDNs-based gene therapy.

MiR-144-5p and miR-21-5p do not drive bone disease in a mouse model of type 1 diabetes mellitus

The increased risk of fractures in patients with type 1 diabetes mellitus (T1DM) is nowadays well recognized. However, the exact mechanism of action of diabetic bone disease has not been fully elucidated. MicroRNAs (miRNAs) are gene regulators that operate post-transcriptionally and have been implicated in the development of various metabolic disorders including T1DM. Previous studies have implicated a role for miR-144-5p and miR-21-5p, which are involved in controlling oxidative stress by targeting Nrf2, in T1DM. To date, it is unclear whether miR-144-5p and miR-21-5p affect bone health in T1DM. Thus, this study aimed to investigate the influence of miR-144-5p and miR-21-5p knockdown in the development of bone disease in T1DM male mice. Therefore, T1DM was induced in 10-wk-old male mice using streptozotocin (STZ). One week later, after development of hyperglycemia, antagomir-144-5p and antagomir-21-5p or their non-targeting control were administered at 10 mg/kg BW once a week until the end of the experiment. At 14 wk of age, glucose levels, bone, and fat mass were analyzed. The results revealed that treating T1DM male mice with antagomir-144-5p and antagomir-21-5p did not protect against diabetes development or bone loss, despite the successful downregulation of the miRNAs and the normalization of Nrf2 mRNA levels in bone tissue. Histological and serological parameters of bone formation or resorption were not altered by the antagomir treatment. Finally, we measured the expression of miRNA-144-5p or miRNA-21-5p in the serum of 30 individuals with T1DM and compared them to non-diabetic controls, but did not find an altered expression of either miRNA. In conclusion, the knockdown of miR-144-5p and miR-21-5p does not affect STZ-induced diabetes development or loss of bone mass in male mice. However, it does normalize expression of the anti-oxidant factor Nrf2 in diabetic bone tissue.

Mitochondrial dysfunction and therapeutic perspectives in osteoporosis

Osteoporosis (OP) is a systemic skeletal disorder characterized by reduced bone mass and structural deterioration of bone tissue, resulting in heightened vulnerability to fractures due to increased bone fragility. This condition primarily arises from an imbalance between the processes of bone resorption and formation. Mitochondrial dysfunction has been reported to potentially constitute one of the most crucial mechanisms influencing the pathogenesis of osteoporosis. In essence, mitochondria play a crucial role in maintaining the delicate equilibrium between bone formation and resorption, thereby ensuring optimal skeletal health. Nevertheless, disruption of this delicate balance can arise as a consequence of mitochondrial dysfunction. In dysfunctional mitochondria, the mitochondrial electron transport chain (ETC) becomes uncoupled, resulting in reduced ATP synthesis and increased generation of reactive oxygen species (ROS). Reinforcement of mitochondrial dysfunction is further exacerbated by the accumulation of aberrant mitochondria. In this review, we investigated and analyzed the correlation between mitochondrial dysfunction, encompassing mitochondrial DNA (mtDNA) alterations, oxidative phosphorylation (OXPHOS) impairment, mitophagy dysregulation, defects in mitochondrial biogenesis and dynamics, as well as excessive ROS accumulation, with regards to OP (Figure 1). Furthermore, we explore prospective strategies currently available for modulating mitochondria to ameliorate osteoporosis. Undoubtedly, certain therapeutic strategies still require further investigation to ensure their safety and efficacy as clinical treatments. However, from a mitochondrial perspective, the potential for establishing effective and safe therapeutic approaches for osteoporosis appears promising.

Regulation Mechanisms and Maintenance Strategies of Stemness in Mesenchymal Stem Cells

Stemness pertains to the intrinsic ability of mesenchymal stem cells (MSCs) to undergo self-renewal and differentiate into multiple lineages, while simultaneously impeding their differentiation and preserving crucial differentiating genes in a state of quiescence and equilibrium. Owing to their favorable attributes, including uncomplicated isolation protocols, ethical compliance, and ease of procurement, MSCs have become a focal point of inquiry in the domains of regenerative medicine and tissue engineering. As age increases or ex vivo cultivation is prolonged, the functionality of MSCs decreases and their stemness gradually diminishes, thereby limiting their potential therapeutic applications. Despite the existence of several uncertainties surrounding the comprehension of MSC stemness, considerable advancements have been achieved in the clarification of the potential mechanisms that lead to stemness loss, as well as the associated strategies for stemness maintenance. This comprehensive review provides a systematic overview of the factors influencing the preservation of MSC stemness, the molecular mechanisms governing it, the strategies for its maintenance, and the therapeutic potential associated with stemness. Finally, we underscore the obstacles and prospective avenues in present investigations, providing innovative perspectives and opportunities for the preservation and therapeutic utilization of MSC stemness.

The role of WWP1 and WWP2 in bone/cartilage development and diseases

Bone and cartilage diseases are often associated with trauma and senescence, manifested as pain and limited mobility. The repair of bone and cartilage lesion by mesenchymal stem cells is regulated by various transcription factors. WW domain-containing protein 1 (WWP1) and WW domain-containing protein 2 (WWP2) are named for WW domain which recognizes PPXY (phono Ser Pro and Pro Arg) motifs of substrate. WWP1and WWP2 are prominent components of the homologous to the E6-AP carboxyl terminus (HECT) subfamily, a group of the ubiquitin ligase. Recently, some studies have found that WWP1 and WWP2 play an important role in the pathogenesis of bone and cartilage diseases and regulate the level and the transactivation of various transcription factors through ubiquitination. Therefore, this review summarizes the distribution and effects of WWP1 and WWP2 in the development of bone and cartilage, discusses the potential mechanism and therapeutic drugs in bone and cartilage diseases such as osteoarthritis, fracture, and osteoporosis.

Cellular senescence in skeletal disease: mechanisms and treatment

The musculoskeletal system supports the movement of the entire body and provides blood production while acting as an endocrine organ. With aging, the balance of bone homeostasis is disrupted, leading to bone loss and degenerative diseases, such as osteoporosis, osteoarthritis, and intervertebral disc degeneration. Skeletal diseases have a profound impact on the motor and cognitive abilities of the elderly, thus creating a major challenge for both global health and the economy. Cellular senescence is caused by various genotoxic stressors and results in permanent cell cycle arrest, which is considered to be the underlying mechanism of aging. During aging, senescent cells (SnCs) tend to aggregate in the bone and trigger chronic inflammation by releasing senescence-associated secretory phenotypic factors. Multiple signalling pathways are involved in regulating cellular senescence in bone and bone marrow microenvironments. Targeted SnCs alleviate age-related degenerative diseases. However, the association between senescence and age-related diseases remains unclear. This review summarises the fundamental role of senescence in age-related skeletal diseases, highlights the signalling pathways that mediate senescence, and discusses potential therapeutic strategies for targeting SnCs.

Milk-Derived Small Extracellular Vesicles Promote Osteogenic Differentiation and Inhibit Inflammation via microRNA-21

Chronic apical periodontitis (CAP) is a disease with characteristics of inflammation and bone loss. In this study, our objective was to examine the function of small extracellular vesicles (sEVs) obtained from milk in encouraging osteogenic differentiation and inhibiting inflammation by miR-21 in CAP. The expression of miR-21 was detected using qRT-PCR in human CAP samples. The impact of miR-21 on the process of osteogenic differentiation was investigated using CCK-8, qRT-PCR, immunofluorescence staining, and Western blot analysis. The evaluation of RAW 264.7 cell polarization and the assessment of inflammatory factor expression were conducted through qRT-PCR. The influence of sEVs on MC3T3-E1 cells and RAW 264.7 cells was examined, with a particular emphasis on the involvement of miR-21. In human CAP samples, a decrease in miR-21 expression was observed. MiR-21 increased the expression of osteogenesis-related genes and M2 polarization genes while decreasing the expression of M1 polarization genes and inflammatory cytokines. Treatment with milk-derived sEVs also promoted osteogenesis and M2 polarization while inhibiting M1 polarization and inflammation. Conversely, the addition of miR-21 inhibitors resulted in opposite effects. Our results indicated that sEVs derived from milk had a positive effect on bone formation and activation of anti-inflammatory (M2) macrophages and simultaneously reduced inflammation by regulating miR-21 in CAP.