Role of Nampt in Regulating the Senescence of Bone Marrow Mesenchymal Stem Cells and Senile Osteoporosis

The objective of this study is to delve into the pathogenesis of senile osteoporosis (SOP) and explore the role of nicotinamide phosphoribosyltransferase (NAMPT) in the aging process of bone marrow mesenchymal stem cells (BMSCs), its impact on osteogenic differentiation, and the efficacy of the small molecule compound P7C3-A20 as a potential therapeutic strategy for SOP. C57BL/6 mice were purchased from the Laboratory Animal Center of Soochow University. All experiments comply with relevant animal ethics regulations and have been approved by the Ethics Committee of Soochow University (SUDA20231215A04). Expression levels of NAMPT, NAD, and mitochondrial complex I subunit NDUFA4L2 were assessed through Western blot (WB), immunofluorescence, and histochemistry. Single-cell transcriptome sequencing was employed to analyze gene expression differences among BMSC cell subpopulations. Ex vivo and in vivo experiments were conducted to evaluate the effects of NAMPT on BMSC aging, osteogenic, and adipogenic differentiation through lentiviral-mediated overexpression or knockdown, and CRISPR-Cas9 gene editing. BMSCs and conditional knockout mice ( Nampt fl/fl ; Prrx1 CreERT2 ) were treated with P7C3-A20 to observe its effects on mitochondrial function, senescence markers, and osteogenic capacity. The study found that NAMPT expression significantly decreased in BMSCs of aged mice, correlating with bone density and metabolic markers. Overexpression of Nampt notably reduced the expression of senescence-associated proteins in aging BMSCs and promoted osteogenic differentiation while inhibiting adipogenic differentiation. The downregulation of NAMPT was associated with decreased NDUFA4L2 expression and mitochondrial dysfunction. Treatment with P7C3-A20 improved mitochondrial function in aging BMSCs, reduced senescence markers, promoted osteogenic differentiation, and alleviated bone loss in the aged osteoporosis mouse model. The findings suggest that NAMPT plays a pivotal role in BMSC aging and the pathogenesis of SOP, potentially by regulating mitochondrial function and energy metabolism in the aging process. Reduced NAMPT expression may lead to mitochondrial dysfunction, affecting the osteogenic differentiation capacity of BMSCs, reducing bone formation, increasing bone marrow fat accumulation, and ultimately resulting in SOP. P7C3-A20, as a specific agonist of NAMPT, has shown inhibitory effects on senescence at the cellular level and has also confirmed its positive effects on bone mass maintenance in animal models, providing a novel therapeutic strategy for SOP.