Resistin as a new player in the regulation of porcine corpus luteum luteolysis: in vitro effect on proliferation/viability, apoptosis and autophagy.

The formation and luteolysis of the corpus luteum (CL) is strictly controlled by many factors. Imbalance between proliferation and apoptosis processes leads to deficiency of the luteal phase and infertility. Our previous study showed resistin expression in porcine luteal cells and an inhibitory effect on progesterone synthesis. Thus, the aim of the present study was to examine the in vitro effect of resistin on the proliferation/viability, apoptosis and autophagy of porcine luteal cells as well as the involvement of mitogen-activated kinase (MAP3/1), protein kinase B (AKT) and signal transducer and activator of transcription 3 (STAT3) in these processes. Porcine luteal cells were incubated with resistin (0.1-10 ng/mL) for 24-72 h and viability was assessed using the alamarBlue or 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Then, the time-dependent effect of resistin on mRNA and protein expression of proliferating cell nuclear antigen (PCNA), caspase 3, BCL2-like protein 4 (BAX), B-cell lymphoma 2 (BCL2), beclin1, microtubule-associated protein 1A/1B-light chain 3 (LC3) and lysosomal-associated membrane protein 1 (LAMP1) was measured by real-time polymerase chain reaction (PCR) and immunoblotting, respectively. We found that resistin enhanced luteal cell viability with no effect on caspase 3 mRNA and protein, increased the BAX/BCL2 mRNA and protein ratio and significantly stimulated the initiation of autophagy, which promotes the maintenance of CL function rather than its regression. Additionally, using pharmacological inhibitors of MAP3/1 (PD98059), AKT (LY294002) and STAT3 (AG490), we observed that the effect of resistin was reversed to the control level in viability and, by influence, MAP3/1 and STAT3 in autophagy. Taken together, our results suggest that resistin, in addition to its well-known effect on granulosa cell function has direct influence on CL luteolysis and the formation and maintenance of luteal cell function.