Vascular endothelial growth factor B regulates insulin secretion in β cells of type 2 diabetes mellitus mice via PLCγ and the IP3R‑evoked Ca2+/CaMK2 signaling pathway

Knockdown of VEGF-B improves HFD-induced insulin resistance by enhancing glucose uptake in vascular endothelial cells via the PI3K/Akt pathway

Vascular endothelial growth factor B (VEGF-B) has been suggested to play a crucial role in regulating whole-body glucose homeostasis. However, the involved mechanisms are not fully understood. This study aimed to elucidate the regulatory effects and mechanisms of VEGF-B on glucose uptake in skeletal muscle, focusing on glucose uptake by skeletal muscle cells and vascular endothelial cells. Our results showed that a high-fat diet (HFD) induced significant increase in VEGF-B expression and decrease in glucose uptake by skeletal muscle, accompanied by elevated serum glucose levels. Interestingly, VEGF-B had no direct effect on glucose uptake by skeletal muscle cells (differentiated C2C12). Instead, VEGF-B inhibited glucose uptake of vascular endothelial cells bEnd.3 and subsequent trans-endothelial glucose transport, ultimately resulting in decreased glucose uptake by skeletal muscle cells. Furthermore, VEGF-B suppressed glucose uptake of vascular endothelial cells by downregulating the expression of glucose transporter 1 (GLUT1) through the VEGFR-PI3K/Akt signaling pathway. In vivo, knockdown of VEGF-B in skeletal muscle increased the HFD-impaired glucose uptake of skeletal muscle and improved the HFD-induced glucose intolerance and insulin resistance. This beneficial effect of VEGF-B knockdown was associated with the elevated expression of GLUT1 in the plasma membrane and the activation of the PI3K/Akt pathway in skeletal muscle. In conclusion, our findings demonstrated that knockdown of VEGF-B improved HFD-induced insulin resistance by enhancing glucose uptake in vascular endothelial cells via the PI3K/Akt pathway. These results highlighted the critical role of VEGF-B in regulating glucose uptake by vascular endothelial cells in skeletal muscle, providing a potential new target for improving obesity-induced glucose homeostasis imbalance.

Comparison of Steroidogenic and Ovulation-Inducing Effects of Orthosteric and Allosteric Agonists of Luteinizing Hormone/Chorionic Gonadotropin Receptor in Immature Female Rats

Gonadotropins, including human chorionic gonadotropin (hCG), are used to induce ovulation, but they have a number of side effects, including ovarian hyperstimulation syndrome (OHSS). A possible alternative is allosteric luteinizing hormone (LH)/hCG receptor agonists, including the compound TP4/2 we developed, which remains active when administered orally. The aim was to study the effectiveness of TP4/2 (orally, 40 mg/kg) as an ovulation inducer in FSH-stimulated immature female rats, compared with hCG (s.c., 15 IU/rat). TP4/2 stimulated progesterone production and corpus luteum formation; time-dependently increased the ovarian expression of steroidogenic genes (Star, Cyp11a1, Cyp17a1) and genes involved in ovulation regulation (Adamts-1, Cox-2, Egr-1, Mt-1); and increased the content of metalloproteinase ADAMTS-1 in the ovaries. These effects were similar to those of hCG, although in some cases they were less pronounced. TP4/2, in contrast to hCG, maintained normal LH levels and increased the ovarian expression of the LH/hCG receptor gene, indicating preservation of ovarian sensitivity to LH, and did not cause a sustained increase in expression of vascular endothelial growth factor-A involved in OHSS. Thus, TP4/2 is an effective ovulation inducer that, unlike hCG, has a lower risk of OHSS and ovarian LH resistance due to its moderate stimulating effect on steroidogenesis.