It is well known that the cornea plays an important role in providing protection to the eye, but it is fragile and vulnerable. To clarify the biological effects and molecular mechanisms of the pituitary adenylate cyclase activating polypeptide (PACAP)-derived peptide MPAPO (named MPAPO) to promote corneal wound healing, we applied a mechanical method to establish a corneal injury model and analyzed the repair effects of MPAPO on corneal injury. MPAPO significantly promoted corneal wound repair in C57BL/6 mice. In addition, we established injury models of epithelial cells and trigeminal ganglion cells with H2O2. The results show that when the concentration of MPAPO is 1 μM, it can significantly promote the repair of injured corneal epithelial cells and the regeneration of trigeminal ganglion cell axons. MPAPO repairs epithelial cells through the promotion of GSK3β phosphorylation by binding to PAC1 and activating AKT. β-catenin escapes the phosphorylation of GSK3β and enters the nucleus to promote the expression of cyclin D1, accelerate cell cycle progression and promote cell proliferation. MPAPO promotes axonal regeneration by binding to the PAC1 receptor and activating adenylate cyclase activity, followed by the cAMP activation of protein kinase A activity and the promotion of CREB phosphorylation. Phosphorylated CREB promotes Bcl2 expression and axonal regeneration. In conclusion, our data support the role of MPAPO to facilitate corneal wound healing by promoting corneal epithelial cell proliferation and trigeminal ganglion cell axon regeneration.

Obesity is strongly linked to male infertility. Testicular spermatogenic cell apoptosis plays an important role in obesity-related male infertility. Pituitary adenylate cyclaseactivating peptide (PACAP) has been recently shown to exhibit antiapoptotic and antidiabetic effects. However, the effects of PACAP on obesity-related male infertility remain unknown. The purpose of the current study is to explore the role of PACAP in obesity-related male infertility. Here, C57BL/6 male mice were fed with a high-fat diet to induce obesity and then treated with PACAP. PACAP treatment ameliorated obesity characteristics, including body weight, epididymal adipose weight, testes/body weight, serum lipids levels, and reproductive hormone levels in vivo. Additionally, PACAP was shown to improve the reproductive function of the obese mice, which was characterized by improved testis morphology, sperm parameters, acrosome reaction, and embryo quality after in vitro fertilization via silent information regulator 1 (Sirt1) activation and p53 deacetylation. These beneficial effects of PACAP were abolished in obese mice with testis-specific knockdown of Sirt1. The mechanism studies showed that PACAP selectively binds to the PAC1 receptor to attenuate palmitic acid-induced mouse spermatogenic cell (GC-1) apoptosis via the PKA/CREB/Sirt1/p53 pathway. However, this mechanism was inhibited in GC-1 cells lacking Sirt1. Finally, human semen studies showed that the decline in sperm quality in obese infertile men was partly due to Sirt1 downregulation and p53 acetylation. Our data suggest that PACAP could ameliorate fertility in obese male mice and may be a promising candidate drug for obesity-induced male infertility.

Obesity is strongly linked to male infertility. Apoptotic inflammatory response caused by oxidative stress in testicular spermatogenic cells is one of the important causes of obesity-related male infertility. Pituitary adenylate cyclase activating polypeptide (PACAP) as a bioactive peptide secreted by the pituitary gland, has a powerful triple role of anti-oxidation, anti-apoptosis and anti-inflammation, and is involved in male reproduction regulation, but the specific mechanism remains unknown. The purpose of the current study is to explore the role of PACAP in obesity-related male infertility. In cell-level experiments, Mouse spermatocytes (GC-2) were treated with palmitate (PA) to establish an high-fat injury cell model in vitro and then treated with PACAP. In animal-level experiments, C57BL/6 male mice were fed with a high-fat diet (HFD) to induce obesity and then treated with PACAP. The cell mechanism studies showed that PACAP selectively binds to the PAC1 receptor to attenuate palmitic acid-induced mouse spermatogenic cell (GC-2) oxidative damage and apoptotic inflammatory response via the PKA/ERK/Nrf2 signaling axis. However, this mechanism was inhibited in GC-2 cells inhibiting the activity of Nrf2. The animal experiment studies showed that PACAP treatment ameliorated obesity characteristics, including body weight, epididymal adipose weight, testes/body weight, serum lipids levels, and reproductive hormone levels in vivo. Additionally, PACAP was shown to improve the reproductive function of the obese mice, which was characterized by improved testis morphology and sperm parameters via Keap1/Nrf2/ARE pathway. These beneficial effects of PACAP were abolished in obese mice with testis-specific knockdown of Nrf2.