AMP-activated protein kinase negatively regulates heat treatment-induced lactate secretion in cultured boar sertoli cells

Effect of tannic acid on adiponectin and gonads in male Brandt's voles (Lasiopodomys brandtii)

Adiponectin regulates steroid production and influences gonadal development. This study examined the effects of tannic acid (TA) on the adiponectin levels and gonads of male Brandt's voles. Male Brandt's voles aged 90 d were randomly separated into three groups: a control group (provided distilled water), a group given 600 mg∙kg-1 TA, and a group that received 1200 mg∙kg-1 TA (continuous gavage for 18 d). In this study, we examined the effects of TA on the adiponectin, antioxidant, and inflammatory levels in the testes. Furthermore, we examined the expression of important regulatory elements that influence adiponectin expression and glucose utilisation. In addition, the body weight, reproductive organ weight, and testicular shape were assessed. Our study observed that TA treatment increased serum adiponectin levels, DsbA-L and Ero1-Lα transcription levels, and AdipoR1, AMPK, GLUT1, and MCT4 expression levels in testicular tissue. TA enhanced pyruvate and lactic acid levels in the testicular tissue, boosted catalase activity, and reduced MDA concentrations. TA reduced the release of inflammatory factors in the testicular tissues of male Brandt's voles. TA increased the inner diameter of the seminiferous tubules. In conclusion, TA appears to stimulate adiponectin secretion and gonadal growth in male Brandt's voles while acting as an antioxidant and anti-inflammatory agent.

Melatonin alleviates the heat stress-induced impairment of Sertoli cells by reprogramming glucose metabolism

Sertoli cells (SCs) provide structural and nutritional support for developing germ cells. Normal glucose metabolism of SCs is necessary for spermatogenesis. Melatonin could alleviate the effects of heat stress on spermatogenesis. However, the influences of heat stress on glucose metabolism in SCs remain unclear, and the potential protective mechanisms of melatonin on SCs need more exploration. In this study, boar SCs were treated at 43°C for 30 min, and different concentrations of melatonin were added to protect SCs from heat stress-induced impairment. These results showed that heat stress-induced oxidative stress caused cell apoptosis, inhibited the pentose phosphate pathway, and decreased the ATP content. Furthermore, heat stress increased the expressions of glucose intake- and glycolytic-related enzymes, which enhanced the glycolysis activity to compensate for the energy deficit. Melatonin relieved heat stress-induced oxidative stress and apoptosis by activating the Kelch-like ECH-associated protein 1 (KEAP1)/NF-E2-related factor 2 signaling pathway to increase the capacity of antioxidants. In addition, melatonin enhanced heat-shock protein 90 (HSP90) expression through melatonin receptor 1B (MTNR1B), thereby stabilizing hypoxia-inducible factor-1α (HIF-1α). Activation of the HIF-1α signaling pathway enhanced glycolysis, promoted the pentose phosphate pathway, and increased cell viability. Our results suggest that melatonin reprograms glucose metabolism in SCs through the MTNR1B-HSP90-HIF-1α axis and provides a theoretical basis for preventing heat stress injury.

Nonylphenol inhibited HIF-1alpha regulated aerobic glycolysis and induced ROS mediated apoptosis in rat Sertoli cells

Nonylphenol (NP) is an endocrine disruptor with reproductive toxicity, which can induce apoptosis of Sertoli cells (SCs). SCs have a high aerobic glycolytic flux to ensure sufficient lactate for germ cells as central energy metabolite, and hypoxia-inducible factors 1alpha (HIF-1α) is a major regulator of glycolysis. This study aimed to investigate whether NP can alter HIF-1α-regulated aerobic glycolysis metabolism and thus induce apoptosis in rat SCs. The results revealed that cell viability, intracellular and extracellular lactate levels, the expression of Hk2, Ldha and Mct4, and the protein levels of HIF-1α, HK2, LDHA and MCT4 were decreased significantly when rat SCs exposed to 20 and 30 μM NP for 24 h. Compared with the 30 μM NP group, the protein levels of HIF-1α, HK2 and LDHA, the expression of Hk2 and Ldha and intracellular lactate levels were increased in 30 μM NP and 125 μM cobalt chloride (CoCl₂, inhibitor of HIF-1α proteasome-mediated degradation) co-treated group. Furthermore, the elevation of reactive oxygen species (ROS) and apoptosis induced by 30 μM NP were also reversed. In summary, exposure to NP inhibited the ability of SCs to produce and secrete lactate. Meanwhile, NP exposure could lead to a decrease in HIF-1α thereby inhibiting aerobic glycolysis in rat SCs, disrupting intracellular homeostasis and further inducing ROS-mediated apoptosis. This research is the first to explore the NP toxicity on SCs function with respect to nutrition support to germ cells, and provide new evidence on the inhibition of aerobic glycolysis inducing ROS-mediated apoptosis in SCs.

Nrf2 activation mediates the protection of mouse Sertoli Cells damage under acute heat stress conditions

Heat stress is known to negatively impact the reproductive process of livestock, which inevitably leads to a decline in animal fertility. Nuclear factor E2-related factor 2 (Nrf2) is an inducible transcription factor, which is essential for maintaining redox signal transmission against oxidative stress. However, there is no reliable research on the response mechanism of Sertoli Cells (SCs) against heat stress and the activation of Nrf2 when SCs are exposed to heat stress. Here, we used primary mouse SCs and SCs line TM4, along with Nrf2 specific inhibitor to determine the reaction mechanism of SCs to maintain intracellular redox homeostasis and self-survival by activating Nrf2. We found that acute heat stress only affected the vitality of SCs and the expression of functional molecules (tight junction-associated proteins and lactate dehydrogenase A [LDHA]) but did not cause cell apoptosis. When Nrf2 was inhibited, more cell death occurred in TM4 cells post heat stress treatment, along with a greater decrease in cell viability and a significant increase in intracellular ROS levels. Our study clarified for the first time the protective effect of Nrf2 activation on heat stress-induced SCs damage. It explained the possible reasons or mechanisms involved in the survival of SCs, the critical protective cells in the testis, which were not affected by heat stress. This study further improved the response mechanism of SCs in the reproductive injury caused by a high-temperature environment.

Activated AMPK promoted the decrease of lactate production in rat Sertoli cells exposed to Zearalenone

Zearalenone, which is ubiquitous in grains and animal feed, is a mycotoxin that can cause serious damage to animals and humans. Sertoli cells (SCs) can be used to study ZEA male reproductive toxicity in vitro. SCs provide energy for germ cells, where AMPK regulates intracellular energy. In order to explore the regulatory effect of AMPK on ZEA-induced lactate decline, we activated AMPK by AICAR and then inhibited AMPK by Compound C with ZEA-treated SCs for 24 h to detect intracellular lactate production-related indicators. Cell viability in the presence of 20 μmol/L ZEA and either 50 μmol/L AICAR or 5 μmol/L Compound C, respectively, did not damage SCs, and could effectively either activate or inhibit AMPK. Inhibition of AMPK promoted the production of pyruvate and lactate via increased expression of the glycolysis-related genes Pgam1 and the lactate production-related proteins GLUT1, LDHA, and MCT4. Activating AMPK inhibited the production of lactate and pyruvate by suppressing the expression of glycolysis-related genes HK1, Pgam1, and Gpi1 and that of lactate production-related proteins LDHA and MCT4. Zearalenone destroys the energy balance in SCs, activates P-AMPK, which inhibit the production of lactate and pyruvate in SCs. This also leads to the decrease of energy supply of SCs to spermatogenic cells, damages to reproductive system.

Acute heat stress reduces viability but increases lactate secretion of porcine immature Sertoli cells through transcriptome reprogramming

Sertoli cells, important constituents of the somatic niche, supports the growth and development of spermatogonia. Heat stress (HS), among multiple intrinsic and external factors, can induce physiological and biochemical changes in Sertoli cells. However, the underlying molecular mechanism remains largely unclear. Here, we showed that acute heat stress (43 °C, 0.5 h) could reduce cell viability, promote apoptosis, and increase the lactate production of porcine immature Sertoli cells (iSCs) cultured in vitro. Then, transcriptome sequencing identified 126 immediately and 3372 prolonged responded differentially expressed genes (DEGs) after acute heat stress (43 °C, 0.5 h) (HS0.5), and 36 h recovery culture following heat stress (HS0.5-R36), respectively. Enrichment analyses found different signaling pathways: immediate changes including cell response to heat, regulation of cellular response to stress, heat shock protein binding, chaperon-mediated protein folding, and sterol biosynthetic process, but prolonged changes mainly involving cell cycle, regulation of apoptotic process/cell proliferation, reproductive process, P53, PI3K-Akt and Glycolysis/Gluconeogenesis. Furthermore, transcriptional patterns of 9 DEGs (Dnajb1, Traf6, Insig1, Gadd45g, Hdac6, Fkbp4, Serpine1, Pfkp and Galm), and 6 heat shock proteins (HSPs) (Hspa6, Hspb1, Hspd1, HSP90aa1, HSP90ab1 and Hsph1) were validated, as well as the protein pattern of HSP90AA1 via immunostaining and western blot. Taken together, heat stress could initiate immediate changes of heat shock-related genes, and reprogram transcriptome and signaling pathways affecting the viability, apoptosis and metabolite production of pig iSCs.

Ssc-novel-miR-106-5p reduces lipopolysaccharide-induced inflammatory response in porcine endometrial epithelial cells by inhibiting the expression of the target gene mitogen-activated protein kinase kinase kinase 14 (MAP3K14)

As an important gram-negative bacterial outer membrane component, lipopolysaccharide (LPS) plays an important role in bacterial-induced endometritis in sows. However, how LPS induces endometritis is unclear. We stimulated sow endometrial epithelial cells (EECs) with LPS and detected cell viability and tumour necrosis factor-α (TNF-α) and interleukin-1 (IL-1) secretion. LPS affected EEC viability and TNF-α and IL-1 secretion in a dose-dependent manner. LPS induced differential expression in 10 of 393 miRNAs in the EECs (downregulated, nine; upregulated, one). MicroRNA (miRNA) high-throughput sequencing of the LPS-induced EECs plus bioinformatics analysis and the dual-luciferase reporter system revealed a novel miRNA target gene: mitogen-activated protein kinase kinase kinase 14 (MAP3K14). Ssc-novel-miR-106-5p mimic, inhibitor and the nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) phosphorylation inhibitor Bay11-7085 were used to detect EEC nuclear factor-κB phosphorylation levels (p-NF-κB) and TNF-α and IL-1 secretion. MiR-106-5p mimic downregulated MAP3K14 mRNA and protein expression levels, inhibited p-NF-κB levels and decreased IL-1 and TNF-α secretion, whereas miR-106-5p inhibitor had the opposite effect. Bay11-7085 inhibited p-NF-κB expression and TNF-α and IL-1 secretion. These results suggest that LPS downregulates ssc-novel-miR-106-5p expression in sow EECs to increase MAP3K14 expression, which increases p-NF-κB to promote IL-1 and TNF-α secretion.

AMPK Function in Mammalian Spermatozoa

AMP-activated protein kinase AMPK regulates cellular energy by controlling metabolism through the inhibition of anabolic pathways and the simultaneous stimulation of catabolic pathways. Given its central regulator role in cell metabolism, AMPK activity and its regulation have been the focus of relevant investigations, although only a few studies have focused on the AMPK function in the control of spermatozoa's ability to fertilize. This review summarizes the known cellular roles of AMPK that have been identified in mammalian spermatozoa. The involvement of AMPK activity is described in terms of the main physiological functions of mature spermatozoa, particularly in the regulation of suitable sperm motility adapted to the fluctuating extracellular medium, maintenance of the integrity of sperm membranes, and the mitochondrial membrane potential. In addition, the intracellular signaling pathways leading to AMPK activation in mammalian spermatozoa are reviewed. We also discuss the role of AMPK in assisted reproduction techniques, particularly during semen cryopreservation and preservation (at 17 °C). Finally, we reinforce the idea of AMPK as a key signaling kinase in spermatozoa that acts as an essential linker/bridge between metabolism energy and sperm's ability to fertilize.