Mitochondria play an important role in controlling oocyte developmental competence. Our previous studies showed that glycine (Gly) can regulate mitochondrial function and improve oocyte maturation in vitro. However, the mechanisms by which Gly affects mitochondrial function during oocyte maturation in vitro have not been fully investigated. In this study, we induced a mitochondrial damage model in oocytes with the Bcl-2-specific antagonist ABT-199. We investigated whether Gly could reverse the mitochondrial dysfunction caused by ABT-199 exposure and whether it is related to calcium regulation. Our results showed that ABT-199 inhibited cumulus expansion, decreased the oocyte maturation rate and the intracellular glutathione (GSH) level, caused mitochondrial dysfunction, which was confirmed by decreased mitochondrial membrane potential (ΔΨm) and the expression of mitochondrial function-related genes PGC-1α, and increased reactiveoxygenspecies (ROS) levelsand the expression of apoptosis-associated genes Bax, Caspase-3, and Cyto C.More importantly, ABT-199-treated oocytes showed an increase in the intracellular free calcium concentration ([Ca²⁺]i) and had impaired cortical type 1 inositol 1,4,5-trisphosphate receptors (IP₃R1) distribution. Nevertheless, treatment with Gly significantly ameliorated mitochondrial dysfunction, oxidative stress, and apoptosis, and Gly also regulated [Ca²⁺]i levels and IP₃R1 cellular distribution, which further protects oocyte maturation in ABT-199-induced porcine oocytes.Taken together, our results indicate that Gly has a protective action against ABT-199-induced mitochondrial dysfunction in porcine oocytes.

Tetrabromobisphenol (TBBPA) is the most widely used brominated flame retardant in the world and displays toxicity to humans and animals. However, few studies have focused on its impact on oocyte maturation. Here, TBBPA was added to the culture medium of bovine cumulus–oocyte complexes (COCs) to examine its effect on oocytes. We found that TBBPA exposure displayed an adverse influence on oocyte maturation and subsequent embryonic development. The results of this study showed that TBBPA exposure induced oocyte meiotic failure by disturbing the polar-body extrusion of oocytes and the expansion of cumulus cells. We further found that TBBPA exposure led to defective spindle assembly and chromosome alignment. Meanwhile, TBBPA induced oxidative stress and early apoptosis by mediating the expression of superoxide dismutase 2 (SOD2). TBBPA exposure also caused mitochondrial dysfunction, displaying a decrease in mitochondrial membrane potential, mitochondrial content, mtDNA copy number, and ATP levels, which are regulated by the expression of pyruvate dehydrogenase kinase 3 (PDK3). In addition, the developmental competence of oocytes and the quality of blastocysts were also reduced after TBBPA treatment. These results demonstrated that TBBPA exposure impaired oocyte maturation and developmental competence by disrupting both nuclear and cytoplasmic maturation of the oocyte, which might have been caused by oxidative stress induced by mitochondrial dysfunction.

Melatonin has been proved to be involved in testosterone synthesis, but whether melatonin participates in testosterone synthesis by regulating miRNA in Leydig cells is still unclear. The purpose of this study is to clarify the mechanism of melatonin on Leydig cells testosterone synthesis from the perspective of miRNA. Our results showed that melatonin could significantly inhibit testosterone synthesis in rooster Leydig cells. miR-7481-3p and CXCL14 were selected as the target of melatonin based on RNA-seq and miRNA sequencing. The results of dual-luciferase reporter assays showed that miR-7481-3p targeted the 3′-UTR of CXCL14. The overexpression of miR-7481-3p significantly inhibited the expression of CXCL14 and restored the inhibitory role of melatonin testosterone synthesis and the expression of StAR, CYP11A1, and 3β-HSD in rooster Leydig cells. Similarly, interference with CXCL14 could reverse the inhibitory effect of melatonin on the level of testosterone synthesis and the expression of StAR, CYP11A1, and 3β-HSD in rooster Leydig cells. The RNA-seq results showed that melatonin could activate the PI3K/AKT signal pathway. Interference with CXCL14 significantly inhibited the phosphorylation level of PI3K and AKT, and the inhibited PI3K/AKT signal pathway could reverse the inhibitory effect of CXCL14 on testosterone synthesis and the expression of StAR, CYP11A1 and 3β-HSD in rooster Leydig cells. Our results indicated that melatonin inhibits testosterone synthesis by targeting miR-7481-3p/CXCL14 and inhibiting the PI3K/AKT pathway.

Mercury, a prevalent heavy metal, negatively impacts oocyte maturation. However, the exact mechanism by which methylmercury chloride (MMC) affects this process remains elusive. The present study found that MMC administration triggered meiotic failure in oocytes by disrupting cumulus cell expansion, leading to compromised spindle apparatus and altered chromosomal architecture, which are crucial for oocyte development. This disruption is characterized by abnormal microtubule organization and defective chromosome alignment. Additionally, MMC exposure caused oxidative stress-induced apoptosis due to mitochondrial dysfunction, as indicated by decreased mitochondrial membrane potential, mitochondrial content, mitochondrial DNA copy number, and adenosine triphosphate levels. Proteomic analysis identified 97 differentially expressed proteins, including P62, an autophagy marker. Our results confirmed that MMC induced autophagy, particularly through the hyperactivation of the mitochondrial autophagy to remove damaged and normal mitochondria. The mitochondrial reactive oxygen species (ROS) scavenger Mito-TEMPO alleviated oxidative stress and mitochondrial autophagy levels, suggesting that mitochondrial ROS initiates this autophagic response. Notably, MMC activates mitochondrial autophagy via the monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signal pathway due to mitochondrial dysfunction. In vivo studies in mice revealed that MMC exposure decreased reproductive performance, attributed to excessive mitochondrial autophagy leading to reduced oocyte quality. Overall, these findings demonstrate that MMC exposure impairs oocyte maturation via the hyperactivation of mitochondrial autophagy induced by mitochondrial dysfunction.

Nickel, a heavy metal with industrial applications and as a feed additive for livestock, can adversely impact reproductive function and gamete quality when present in excessive amounts in the animal feed environment. In this study, the results indicate that nickel exposure hampers polar body extrusion and cumulus cell expansion, thereby diminishing oocyte quality and developmental competence. Furthermore, nickel exposure reduces glutathione (GSH) levels in oocytes, leading to excessive accumulation of reactive oxygen species (ROS), provoking oxidative stress and mitochondrial impairment. This cascade initiates mitochondrial autophagy, upregulates the expression of autophagy-related proteins Parkin and PINK1, promotes LC3 binding to autophagosomes. Nickel exposure disrupts calcium homeostasis and induces endoplasmic reticulum stress (ERS). Inhibiting ERS effectively alleviates the deterioration of oocytes quality caused by nickel exposure and inhibits mitochondrial autophagy. Proteomics further confirms nickel's exposure detrimental effects on mitochondria and ER, impacting cellular processes. Employing bovine oocytes as a model, consistent phenotypes were observed. These results indicate that nickel exposure disrupts intracellular calcium homeostasis, elicits ERS, disrupts cellular calcium homeostasis, diminishes the quality of pig oocytes, impairs oocyte maturation and developmental potential, and instigates mitochondrial autophagy.