Mesenchymal Stem Cells-Derived Extracellular Vesicles Mimetics as Osteoinductive Mediators for Bone Healing

AUTHORS

Antoine Karoichan, Ling Li, Celine J. Agnes, Bettina M. Willie, Maryam Tabrizian

ABSTRACT

Bone defects remain challenging to treat, with common therapies still relying on invasive approaches. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) offer a promising alternative due to their regenerative and immunomodulatory properties, but challenges in scalable EV production limit clinical translation. Nanoghosts (NGs) are an emerging class of EV-mimetics synthesized through the physical distortion of ghost cells that offer innate bioactivity similar to EVs while having more scalable yields. In this study, the osteogenic potential of NGs made from MSC ghosts (MSC-NGs) is explored for the first time and contrasted with conventional MSC-EVs. MSC-NGs are generated through sonication, yielding two-fold more vesicles compared to MSC-EVs from the same number of cells. Unlike MSC-EVs, MSC-NGs significantly enhanced the osteogenic differentiation of MSCs, evidenced by increased alkaline phosphatase (ALP) activity and early mineralization. Proteomic analysis further revealed that MSC-NGs are more enriched in osteogenesis-related proteins than MSC-EVs. In vivo, treatment of a 0.5 mm mouse femoral osteotomy with MSC-NGs accelerated fracture healing, showing increased callus mineralization by day 14 and improved bone marrow reconstitution by day 21, along with reduced osteoclastic activity. These findings demonstrate MSC-NGs as scalable and effective therapeutics for bone tissue engineering, offering advantages over MSC-EVs in future bone healing strategies.

Cholestyramine alleviates bone and muscle loss in irritable bowel syndrome via regulating bile acid metabolism

AUTHORS

Ming Chen, Wei Wei, Yi Li, Siliang Ge, Junmin Shen, Jiayu Guo, Yu Zhang, Xiang Huang, Xinyu Sun, Dongliang Cheng, Huayong Zheng, Feifan Chang, Junyu Chen, Jiang Liu, Qinxiang Zhang, Tianjunke Zhou, Kang Yu, Peifu Tang

ABSTRACT

Irritable bowel syndrome (IBS) is a widespread gastrointestinal disorder known for its multifaceted pathogenesis and varied extraintestinal manifestations, yet its implications for bone and muscle health are underexplored. Recent studies suggest a link between IBS and musculoskeletal disorders, but a comprehensive understanding remains elusive, especially concerning the role of bile acids (BAs) in this context. This study aimed to elucidate the potential contribution of IBS to bone and muscle deterioration via alterations in gut microbiota and BA profiles, hypothesizing that cholestyramine could counteract these adverse effects. We employed a mouse model to characterize IBS and analysed its impact on bone and muscle health. Our results revealed that IBS promotes bone and muscle loss, accompanied by microbial dysbiosis and elevated BAs. Administering cholestyramine significantly mitigated these effects, highlighting its therapeutic potential. This research not only confirms the critical role of BAs and gut microbiota in IBS-associated bone and muscle loss but also demonstrates the efficacy of cholestyramine in ameliorating these conditions, thereby contributing significantly to the field's understanding and offering a promising avenue for treatment.

The Dietary Fiber Inulin Slows Progression of Chronic Kidney Disease–Mineral Bone Disorder (CKD-MBD) in a Rat Model of CKD

AUTHORS

Annabel Biruete, Neal X. Chen, Corinne E. Metzger, Shruthi Srinivasan, Kalisha O'Neill, Paul B. Fallen, Austin Fonseca, Hannah E. Wilson, Henriette de Loor, Pieter Evenepoel, Kelly S. Swanson, Matthew R. Allen, Sharon M. Moe

ABSTRACT

Chronic kidney disease (CKD)–mineral bone disorder (CKD-MBD) leads to fractures and cardiovascular disease. Observational studies suggest beneficial effects of dietary fiber on both bone and cardiovascular outcomes, but the effect of fiber on CKD-MBD is unknown. To determine the effect of fiber on CKD-MBD, we fed the Cy/+ rat with progressive CKD a casein-based diet of 0.7% phosphate with 10% inulin (fermentable fiber) or cellulose (non-fermentable fiber) from 22 weeks to either 30 or 32 weeks of age (~30% and ~15% of normal kidney function; CKD 4 and 5). We assessed CKD-MBD end points of biochemistry, bone quantity and quality, cardiovascular health, and cecal microbiota and serum gut-derived uremic toxins. Results were analyzed by two-way analysis of variance (ANOVA) to evaluate the main effects of CKD stage and inulin, and their interaction. The results showed that in CKD animals, inulin did not alter kidney function but reduced the increase from stage 4 to 5 in serum levels of phosphate and parathyroid hormone, but not fibroblast growth factor-23 (FGF23). Bone turnover and cortical bone parameters were similarly improved but mechanical properties were not altered. Inulin slowed progression of aorta and cardiac calcification, left ventricular mass index, and fibrosis. To understand the mechanism, we assessed intestinal microbiota and found changes in alpha and beta diversity and significant changes in several taxa with inulin, together with a reduction in circulating gut derived uremic toxins such as indoxyl sulfate and short-chain fatty acids. In conclusion, the addition of the fermentable fiber inulin to the diet of CKD rats led to a slowed progression of CKD-MBD without affecting kidney function, likely mediated by changes in the gut microbiota composition and lowered gut-derived uremic toxins.

Lipolysis supports bone formation by providing osteoblasts with endogenous fatty acid substrates to maintain bioenergetic status

AUTHORS

Ananya Nandy, Ron C. M. Helderman, Santosh Thapa, Shobana Jayapalan, Alison Richards, Nikita Narayani, Michael P. Czech, Clifford J. Rosen & Elizabeth Rendina-Ruedy

ABSTRACT

Bone formation is a highly energy-demanding process that can be impacted by metabolic disorders. Glucose has been considered the principal substrate for osteoblasts, although fatty acids are also important for osteoblast function. Here, we report that osteoblasts can derive energy from endogenous fatty acids stored in lipid droplets via lipolysis and that this process is critical for bone formation. As such, we demonstrate that osteoblasts accumulate lipid droplets that are highly dynamic and provide the molecular mechanism by which they serve as a fuel source for energy generation during osteoblast maturation. Inhibiting cytoplasmic lipolysis leads to both an increase in lipid droplet size in osteoblasts and an impairment in osteoblast function. The fatty acids released by lipolysis from these lipid droplets become critical for cellular energy production as cellular energetics shifts towards oxidative phosphorylation during nutrient-depleted conditions. In vivo, conditional deletion of the ATGL-encoding gene Pnpla2 in osteoblast progenitor cells reduces cortical and trabecular bone parameters and alters skeletal lipid metabolism. Collectively, our data demonstrate that osteoblasts store fatty acids in the form of lipid droplets, which are released via lipolysis to support cellular bioenergetic status when nutrients are limited. Perturbations in this process result in impairment of bone formation, specifically reducing ATP production and overall osteoblast function.

Loss of Notch signaling in skeletal stem cells enhances bone formation with aging

AUTHORS

Lindsey H. Remark, Kevin Leclerc, Malissa Ramsukh, Ziyan Lin, Sooyeon Lee, Backialakshmi Dharmalingam, Lauren Gillinov, Vasudev V. Nayak, Paulo El Parente, Margaux Sambon, Pablo J. Atria, Mohamed A. E. Ali, Lukasz Witek, Alesha B. Castillo, Christopher Y, Park, Ralf H. Adams, Aristotelis Tsirigos, Sophie M. Morgani & Philipp Leucht

ABSTRACT

Skeletal stem and progenitor cells (SSPCs) perform bone maintenance and repair. With age, they produce fewer osteoblasts and more adipocytes leading to a loss of skeletal integrity. The molecular mechanisms that underlie this detrimental transformation are largely unknown. Single-cell RNA sequencing revealed that Notch signaling becomes elevated in SSPCs during aging. To examine the role of increased Notch activity, we deleted Nicastrin, an essential Notch pathway component, in SSPCs in vivo. Middle-aged conditional knockout mice displayed elevated SSPC osteo-lineage gene expression, increased trabecular bone mass, reduced bone marrow adiposity, and enhanced bone repair. Thus, Notch regulates SSPC cell fate decisions, and moderating Notch signaling ameliorates the skeletal aging phenotype, increasing bone mass even beyond that of young mice. Finally, we identified the transcription factor Ebf3 as a downstream mediator of Notch signaling in SSPCs that is dysregulated with aging, highlighting it as a promising therapeutic target to rejuvenate the aged skeleton.

β-Arrestin 2 knockout prevents bone loss in response to continuous parathyroid hormone stimulation in male and female mice

AUTHORS

Gilberto Li Feng, Marc D Grynpas & Jane Mitchell

ABSTRACT

Background

β-Arrestin 2 (β-arr2) binds activated parathyroid hormone (PTH) receptors stimulating internalization. PTH stimulates both anabolic and catabolic effect on bone depending on the way it is administered. Intermittent PTH stimulation increases trabecular bone formation in mice, but this is decreased in mice lacking β-arr 2, suggesting a role for β-arr 2 in the anabolic effects of PTH. The role of β-arr 2 in the catabolic effects of continuous PTH (cPTH) treatment is not known.

Objective

To assess the effects of cPTH administration on bone in mice lacking β-arr 2 compared to wild-type (WT).

Methods

Groups of male and female WT or β-arr2 knockout (KO) mice were administered either PTH or phosphate-buffered saline by osmotic pumps for 2 weeks. Following treatment, serum calcium and phosphate levels were measured, bone structure and mineral density were measured by microcomputed tomography, and bone cells measured by static and dynamic histomorphometry.

Results

β-arr2 KO had no effects on skeletal development in mice of either sex. PTH treatment caused hypercalcemia and hypophosphatemia and decreased trabecular and cortical bone only in male WT mice. β-arr2 KO in male mice completely abrogated the effects of PTH on bone, while in female β-arr2 KO mice, PTH treatment increased trabecular bone with no effects on cortical bone.

Conclusions

These results demonstrate a profound sex effect on skeletal responses to cPTH treatment, suggesting a protective effect of estrogen on bone loss. β-arr2 plays a role in restraining the anabolic effects of PTH in both male and female mice.