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.

Enhanced fatty acid oxidation in osteoprogenitor cells provides protection from high-fat diet induced bone dysfunction

AUTHORS

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

ABSTRACT

Bone homeostasis within the skeletal system is predominantly maintained by bone formation and resorption, where formation of new bone involves maturation of stromal cells to mineral and matrix secreting mature osteoblasts, which requires cellular energy or adenosine triphosphate. Alterations in systemic metabolism can influence osteoblast function. In line with this, type 2 diabetes mellitus (T2DM), a common metabolic disorder is also associated with reduced bone formation and increased risk of fracture. Impairment in lipid metabolism is one of the key features associated with T2DM-related pathologies in multiple tissues. Therefore, we tested the hypothesis that the reduced bone formation reported in obese murine models of impaired glucose tolerance is a function of disrupted lipid metabolism in osteoblasts. We first confirmed that mice fed a high-fat diet (HFD) have reduced bone microarchitecture along with lower bone formation rates. Interestingly, osteoblasts from obese mice harbor higher numbers of cytosolic lipid droplets along with decreased bioenergetic profiles compared to control cells. Further supporting this observation, bone cortex demonstrated higher total lipid content in HFD fed mice compared to control-fed mice. As a further proof of principle, we generated a novel murine model to conditionally delete Plin2 in osteoblast-progenitor cells using Prrx1-Cre, to enhance lipid droplet breakdown. Our data demonstrate that knocking down Plin2 in an osteoprogenitor specific manner protects from HFD induced osteoblast dysfunction. Furthermore, the mechanism of action involves enhanced osteoblast fatty acid oxidation. In conclusion, the current studies establish that HFD induced glucose intolerance leads to perturbations in osteoblast lipid metabolism, thus causing lower bone formation, which can be protected against by increasing fatty acid oxidation.

The MCP-3/Ccr3 axis contributes to increased bone mass by affecting osteoblast and osteoclast differentiation

AUTHORS

Jung Ha Kim, Kabsun Kim, Inyoung Kim, Semun Seong, Xiangguo Che, Je-Yong Choi, Jeong-Tae Koh, Nacksung Kim

ABSTRACT

Several CC subfamily chemokines have been reported to regulate bone metabolism by affecting osteoblast or osteoclast differentiation. However, the role of monocyte chemotactic protein 3 (MCP-3), a CC chemokine, in bone remodeling is not well understood. Here, we show that MCP-3 regulates bone remodeling by promoting osteoblast differentiation and inhibiting osteoclast differentiation. In a Ccr3-dependent manner, MCP-3 promoted osteoblast differentiation by stimulating p38 phosphorylation and suppressed osteoclast differentiation by upregulating interferon beta. MCP-3 increased bone morphogenetic protein 2-induced ectopic bone formation, and mice with MCP-3-overexpressing osteoblast precursor cells presented increased bone mass. Moreover, MCP-3 exhibited therapeutic effects by abrogating receptor activator of nuclear factor kappa-B ligand-induced bone loss. Therefore, MCP-3 has therapeutic potential for diseases involving bone loss due to its positive role in osteoblast differentiation and negative role in osteoclast differentiation.

Girk3 deletion increases osteoblast maturation and bone mass accrual in adult male mice

AUTHORS

Samantha R Weaver, Haydee M Torres, Katherine M Arnold, Elizabeth L Zars, Eduardo Peralta-Herrera, Earnest L Taylor, Kanglun Yu, Ezequiel Marron Fernandez de Velasco, Kevin Wickman, Meghan E McGee-Lawrence, Elizabeth W Bradley, Jennifer J Westendorf

ABSTRACT

Osteoporosis and other metabolic bone diseases are prevalent in the aging population. While bone has the capacity to regenerate throughout life, bone formation rates decline with age and contribute to reduced bone density and strength. Identifying mechanisms and pathways that increase bone accrual in adults could prevent fractures and accelerate healing. G protein-gated inwardly rectifying K+ (GIRK) channels are key effectors of G protein-coupled receptor signaling. Girk3 was recently shown to regulate endochondral ossification. Here, we demonstrate that deletion of Girk3 increases bone mass after 18 weeks of age. Male 24-week-old Girk3-/- mice have greater trabecular bone mineral density and bone volume fraction than wildtype (WT) mice. Osteoblast activity is moderately increased in 24-week-old Girk3-/- mice compared to WT mice. In vitro, Girk3-/- bone marrow stromal cells (BMSCs) are more proliferative than WT BMSCs. Calvarial osteoblasts and BMSCs from Girk3-/- mice are also more osteogenic than WT cells, with altered expression of genes that regulate the wingless-related integration site (Wnt) family. Wnt inhibition via Dickkopf-1 (Dkk1) or β-catenin inhibition via XAV939 prevents enhanced mineralization, but not proliferation, in Girk3-/- BMSCs and slows these processes in WT cells. Finally, selective ablation of Girk3 from cells expressing Cre recombinase from the 2.3 kb-Col1a1 promoter, including osteoblasts and osteocytes, is sufficient to increase bone mass and bone strength in male mice at 24 weeks of age. Taken together, these data demonstrate that Girk3 regulates progenitor cell proliferation, osteoblast differentiation, and bone mass accrual in adult male mice.

Osteoblastic erythropoietin is not required for bone mass accrual

AUTHORS

Giulia Lanzolla, Christophe Merceron, Mohd Parvez Khan, Elena Sabini, Amato Giaccia, Ernestina Schipani

ABSTRACT

Erythropoietin, primarily produced by interstitial fibroblasts in the kidney during adulthood, and its receptor are well-known for their crucial role in regulating erythropoiesis. Recent research has unveiled an additional function of circulating erythropoietin in the control of bone mass accrual and homeostasis through its receptor, which is expressed in both osteoblasts and osteoclasts. Notably, cells of the osteoblast lineage can produce and secrete functional erythropoietin upon activation of the hypoxia signaling pathway. However, the physiological relevance of osteoblastic erythropoietin remains to be fully elucidated.

This study aimed to investigate the potential role of osteoblastic erythropoietin in regulating bone mass accrual and erythropoiesis in young adult mice. To accomplish this, we employed a mutant mouse model lacking erythropoietin specifically in mesenchymal progenitors and their descendants. Our findings indicate that in vivo loss of erythropoietin in the osteoblast lineage does not significantly affect either bone mass accrual or erythropoiesis in young adult mice. Further investigations are necessary to comprehensively understand the potential contribution of erythropoietin produced and secreted by osteoblast cells during aging, repair and under pathological conditions.

In vivo effects of cell seeding technique in an ex vivo regional gene therapy model for bone regeneration

AUTHORS

Jennifer A. Bell, Cory K. Mayfield, Kevin Collon, Stephanie Chang, Matthew C. Gallo, Elizabeth Lechtholz-Zey, Mina Ayad, Osamu Sugiyam, Amy H. Tang, Sang-Hyun Park, Jay R. Lieberman

ABSTRACT

When delivering cells on a scaffold to treat a bone defect, the cell seeding technique determines the number and distribution of cells within a scaffold, however the optimal technique has not been established. This study investigated if human adipose-derived stem cells (ASCs) transduced with a lentiviral vector to overexpress bone morphogenetic protein 2 (BMP-2) and loaded on a scaffold using dynamic orbital shaker could reduce the total cell dose required to heal a critical sized bone defect when compared with static seeding. Human ASCs were loaded onto a collagen/biphasic ceramic scaffold using static loading and dynamic orbital shaker techniques, compared with our labs standard loading technique, and implanted into femoral defects of nude rats. Both a low dose and standard dose of transduced cells were evaluated. Outcomes investigated included BMP-2 production, radiographic healing, micro-computerized tomography, histologic assessment, and biomechanical torsional testing. BMP-2 production was higher in the orbital shaker cohort compared with the static seeding cohort. No statistically significant differences were noted in radiographic, histomorphometric, and biomechanical outcomes between the low-dose static and dynamic seeding groups, however the standard-dose static seeding cohort had superior biomechanical properties. The standard-dose 5 million cell dose standard loading cohort had superior maximum torque and torsional stiffness on biomechanical testing. The use of orbital shaker technique was labor intensive and did not provide equivalent biomechanical results with the use of fewer cells.