Protective Effects of Velvet Antler Polypeptides on Cyclophosphamide-Induced Myelosuppression in Mouse and Bone Marrow Mesenchymal Stem Cells

<b>Background:</b> Myelosuppression is one of the most common chemotherapy side effects, seriously threatening the quality of life of cancer patients. Studies have shown that velvet antler polypeptides (VAPs) could enhance immunity and anti-aging and also have a hematopoietic-promoting effect. However, there are relatively few studies on the treatment of myelosuppression with VAPs, and the therapeutic mechanism remains unclear. <b>Methods:</b> This study employed both in vitro and in vivo models to explore the mechanism of VAPs against myelosuppression. In this study, the cyclophosphamide (CTX)-induced bone marrow mesenchymal stem cell (BMSC) injury model was used to evaluate the effects of VAPs on cell viability, apoptosis, reactive oxygen species activity, and protein expression. Furthermore, a CTX-induced myelosuppression mouse model was employed to evaluate peripheral blood counts, organ indices, femoral tissue histopathology, immunohistochemical expression of CD34, VEGF, and Notch1, and key proteins in the Notch1/PI3K/AKT pathway in vivo. <b>Results:</b> Our results showed that VAPs protected BMSCs from CTX-induced apoptosis, inhibited ROS production, and promoted the secretion of VEGF, TPO, and VCAM-1, thereby improving the bone marrow microenvironment. Furthermore, the results showed that VAPs improved the peripheral blood counts and bone marrow nucleated cell (BMNC) count in CTX-induced myelosuppression mice and ameliorated pathological injury of the spleen, thymus, and liver. VAPs inhibited the apoptosis of bone marrow cells, manifested by regulating the expression levels of proteins like PI3K/p-PI3K, AKT/p-AKT, Bcl-2, Bax, and Caspase-3. Simultaneously, it upregulated the expression of Notch1 and Hes1 proteins. The application of the PI3K inhibitor LY294002 and the Notch1 inhibitor DAPT demonstrated that the ameliorative effect of VAPs on myelosuppression was dependent on the activation of both the Notch1 and PI3K/AKT pathways. <b>Conclusions:</b> Our study indicates that VAPs may achieve treatment of myelosuppression by improving the hematopoietic microenvironment, inhibiting apoptosis of mouse bone marrow cells, and regulating the Notch1 and PI3K/AKT signaling pathways.