During aging, disruptions in various signaling pathways become more common. Some older patients will exhibit irregular bone morphogenetic protein (BMP) signaling, which can lead to osteoporosis (OP)—a debilitating bone disease resulting from an imbalance between osteoblasts and osteoclasts. In 2002, the Food and Drug Administration (FDA) approved recombinant human BMP-2 (rhBMP-2) for use in spinal fusion surgeries as it is required for bone formation. However, complications with rhBMP-2 arose and primary osteoblasts from OP patients often fail to respond to BMP-2. Although patient samples are available for study, previous medical histories can impact results. Consequently, the C57BL/6 mouse line serves as a valuable model for studying OP and aging. We find that BMP receptor type Ia (BMPRIa) is upregulated in the bone marrow stromal cells (BMSCs) of 15-month-old mice, consistent with prior data. Furthermore, conjugating BMP-2 with Quantum Dots (QDot^®s) allows effective binding to BMPRIa, creating a fluorescent tag for BMP-2. Furthermore, after treating BMSCs with methyl-β-cyclodextrin (MβCD), a disruptor of cellular endocytosis, BMP signaling is restored in 15-month-old mice, as shown by von Kossa assays. MβCD has the potential to restore BMPRIa function, and the BMP signaling pathway offers a promising avenue for future OP therapies.

As humans age, aberrancies in several signaling pathways occur. In the aging population, some patients display abnormal bone morphogenetic protein (BMP) signaling. This can lead to osteoporosis (OP), a debilitating bone disorder caused by an imbalance between osteoblasts and osteoclasts. In 2002, the Food and Drug Administration (FDA) approved usage of recombinant human BMP-2 (rhBMP-2) during spinal fusion surgery as it is crucial for bone formation. However, complications have been reported with rhBMP-2 and primary osteoblasts isolated from OP patients are unresponsive to BMP-2. While patient samples are available, previous medical history may alter results. Therefore, C57BL/6 mice, an aging model that displays aberrant BMP-signaling, can be utilized to investigate OP and aging. We show that BMP receptor type Ia (BMPRIa) is upregulated in the bone marrow stromal cells (BMSCs) of 15-month mice similar to previous data. We show that a conjugation between BMP-2 and Quantum Dots (QDot®s) effectively binds to BMPRIa and can investigate BMP-2 activity. After incubating BMSCs with methyl-β-cyclodextrin (MβCD), BMP-signaling is restored in 15-month mice as shown by western blotting and the von Kossa assay. MβCD may be used to rescue BMPRIa and the BMP-signaling pathway can be utilized by future therapeutics to treat OP.

Bone Morphogenetic Protein-2 (BMP-2) is a growth factor that maintains bone homeostasis through BMP receptor type-I (BMPRIa) and type II (BMPRII). BMP-2 promotes osteogenesis by inducing bone marrow mesenchymal stem cell (BMSC) differentiation into osteoblasts, but it can also trigger BMSC differentiation into adipocytes. BMP-2's osteo-inductive ability has made it a potential treatment for osteoporosis, yet its dual role in BMSC differentiation complicates its efficacy. The mechanisms governing BMP-2-induced adipogenesis remain unclear. High BMP-2 levels cause BMPRIa cleavage, but the downstream effects and determinants of osteogenesis or adipogenesis activation are unresolved. Here, we identify Caspase-1 as a key mediator of BMPRIa cleavage and its downstream effects on adipogenesis. We used primary BMSCs from C57BL/6 mice, stimulated with varying BMP-2 concentrations, to explore BMP-2-induced BMPRIa cleavage and its impact on PPARγ – a key regulator of adipogenesis. Western blotting and immunostaining using antibodies against BMPRIa and PPARγ uncovered BMPRIa cleavage and revealed the nuclear translocation of the cleaved segment, colocalizing with PPARγ. Caspase-1 inhibition significantly reduced BMPRIa cleavage and PPARγ expression, highlighting its pivotal role in adipogenic differentiation. Understanding the molecular mechanisms of BMP-2-induced adipogenesis and Caspase-1 inhibition could improve BMP-2 therapeutic efficacy for osteoporosis by promoting osteogenesis over adipogenesis.

Bone Morphogenetic Protein-2 (BMP2) is a growth factor that maintains bone homeostasis through the BMP receptor type Ia (BMPRIa) and type II (BMPRII). BMP2 promotes osteogenesis by inducing the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts; however, it can also trigger BMSC differentiation into adipocytes. BMP2’s osteo-inductive ability has made it a potential treatment for osteoporosis, yet its dual role in BMSC differentiation complicates its efficacy. High BMP2 levels cause BMPRIa cleavage, but the downstream effects and the mechanisms governing BMP2-induced osteogenesis or adipogenesis are unresolved. Here, we identify Caspase-1 as a key mediator of BMPRIa cleavage and its downstream effects on adipogenesis. We used primary BMSCs from C57BL/6 mice, stimulated with varying BMP2 concentrations, to explore BMP2-induced BMPRIa cleavage and its impact on PPARγ—a key regulator of adipogenesis. Western blotting and immunostaining using antibodies against BMPRIa and PPARγ uncovered BMPRIa cleavage and revealed the nuclear translocation of the cleaved segment, colocalizing with PPARγ. Caspase-1 inhibition significantly reduced BMPRIa cleavage and PPARγ expression, highlighting its pivotal role in adipogenic differentiation. Understanding the molecular mechanisms of BMP2-induced adipogenesis and Caspase-1 inhibition could improve BMP2 therapeutic efficacy for osteoporosis by promoting osteogenesis over adipogenesis.