Hongmin Li

Mettl14, a key component of the m6A methyltransferase complex, plays a crucial role in regulating mRNA stability and splicing. Reduced expression of Mettl14 is associated with hepatocellular carcinoma and liver regeneration, yet the molecular mechanisms by which it regulates the hepatocyte cell cycle remain unclear. Using RNA‐Seq and MeRIP‐Seq in liver‐specific Mettl14 knockout mice, we found that Mettl14 deficiency stabilizes Fam32a mRNA through m6A modifications, resulting in increased Fam32a protein levels. Elevated Fam32a expression accelerates the G1/S transition by modulating Cdkn1a splicing, specifically downregulating its variant 2. These findings uncover a novel m6A‐dependent mechanism that regulates hepatocyte cell cycle progression and highlight the previously unrecognized role of Fam32a in promoting the G1/S transition.

HMGB1, one of the most abundant nuclear non‐histone proteins, also performs extracellular functions, and its nuclear export mechanisms have been extensively studied. Here, a novel mechanism of nuclear export for HMGB1 driven by lactylation is proposed. In addition, it is revealed that hypoxia‐induced lactylation of HMGB1 facilitates its nuclear export in a complex with TIAR, promoting stress granule (SG) formation in the cytosol. Mass spectrometry revealed 12 lysine residues in HMGB1 undergoing lactylation, with K172 and K177 being the most susceptible. Functional studies using lysine‐to‐arginine mutants (K→R) demonstrated that lactylation at K177 is crucial for HMGB1‐TIAR complex export, as K177R mutation completely blocked this export and subsequent SG formation. Notably, this lactylation‐mediated mechanism is specific to hypoxic stress, while other stressors, such as sodium arsenite exposure and heat shock, triggered TIAR nuclear export and SG assembly independently of HMGB1. These findings reveal a previously unrecognized role of HMGB1 lactylation in mediating nuclear export and SG formation under hypoxia.

Background/Objectives: The avascular nature of the follicle creates a hypoxic microenvironment, establishing a niche where granulosa cells (GCs) rely on glycolysis to produce energy in the form of lactate (L-lactate). Autophagy, an evolutionarily conserved stress-response process, involves the formation of autophagosomes to encapsulate intracellular components, delivering them to lysosomes for degradation. This process plays a critical role in maintaining optimal follicular development. However, whether hypoxia regulates autophagy in GCs via lactate remains unclear. Methods: In this study, we investigated lactate-induced autophagy under hypoxia by utilizing glycolysis inhibitors or silencing related genes. Results: We observed a significant increase in autophagy in ovarian GCs under hypoxic conditions, indicated by elevated LC3II levels and reduced P62 levels. Suppressing lactate production through glycolytic inhibitors (2-DG and oxamate) or silencing lactate dehydrogenase (LDHA/LDHB) effectively reduced hypoxia-induced autophagy. Further investigation revealed that the HIF1-α/BNIP3/Beclin-1 axis is essential for lactate-induced autophagy under hypoxic conditions. Inhibiting HIF-1α activity using siRNAs or PX-478 downregulated BNIP3 expression and subsequently suppressed autophagy. Similarly, BNIP3 silencing with siRNAs repressed lactate-induced autophagy in hypoxic conditions. Mechanistically, immunoprecipitation experiments showed that BNIP3 disrupted pre-existing Bcl-2/Beclin-1 complexes by competing with Bcl-2 to form Bcl-2/BNIP3 complexes. This interaction released Beclin-1, which subsequently triggered lactate-induced autophagy under hypoxic conditions. Conclusions: These findings unveil a novel mechanism by which hypoxia regulates GC autophagy through lactate production, highlighting its potential role in sustaining follicular development under hypoxic conditions.

Severe hypoxia induced by vascular compromise (ovarian torsion, surgery), obliteration of vessels (aging, chemotherapy, particularly platinum drugs) can cause massive follicle atresia. On the other hand, hypoxia increases the occurrence of DNA double‐strand breaks (DSBs) and triggers cellular damage repair mechanisms; however, if the damage is not promptly repaired, it can also induce the apoptosis program. Insulin‐like growth factor‐I (IGF‐I) is a polypeptide hormone that plays essential roles in stimulating mammalian follicular development. Here, we report a novel role for IGF‐I in protecting hypoxic GCs from apoptosis by promoting DNA repair through the homologous recombination (HR) process. Indeed, the hypoxic environment within follicles significantly inhibited the efficiency of HR‐directed DNA repair. The presence of IGF‐I‐induced HR pathway to alleviate hypoxia‐induced DNA damage and apoptosis primarily through upregulating the expression of the RAD51 recombinase. Importantly, we identified a new transcriptional regulator of RAD51 , namely E2F8, which mediates the protective effects of IGF‐I on hypoxic GCs by facilitating the transcriptional activation of RAD51 . Furthermore, we demonstrated that the PI3K/AKT pathway is crucial for IGF‐I‐induced E2F8 expression, resulting in increased RAD51 expression and enhanced HR activity, which mitigates hypoxia‐induced DNA damage and thereby protects against GCs apoptosis. Together, these findings define a novel mechanism of IGF‐I‐mediated GCs protection by activating the HR repair through the PI3K/AKT/E2F8/RAD51 pathway under hypoxia.

Numerous studies have established that the hypoxic conditions within ovarian follicles induce apoptosis in granulosa cells (GCs), a pivotal hallmark of follicular atresia. Melatonin (N-acetyl-5-methoxytryptamine, MT), a versatile antioxidant naturally present in follicular fluid, acts as a safeguard for maintaining GCs’ survival during stress exposure. In this study, we unveil an innovative protective mechanism of melatonin against hypoxia-triggered GC apoptosis by selectively inhibiting mitochondrial ROS (mtROS) generation. Specifically, under hypoxic conditions, a gradual accumulation of mitochondrial ROS occurred, consequently activating the JNK-FOXO1 pathway, and driving GCs toward apoptosis. The blocking of JNK or FOXO1 diminished hypoxia-induced GC apoptosis, but this effect was nullified in the presence of GSH, indicating that mtROS instigates apoptosis through the JNK-FOXO1 pathway. Consistent with this, hypoxic GCs treated with melatonin exhibited decreased levels of mtROS, reduced JNK-FOXO1 activation, and mitigated apoptosis. However, the protective capabilities of melatonin were attenuated upon inhibiting its receptor MTNR1B, accompanied by the decreased expression of antioxidant genes. Notably, SOD2, a key mitochondrial antioxidant gene modulated by the melatonin–MTNR1B axis, effectively inhibited the activation of mtROS-JNK-FOXO1 and subsequent apoptosis, whereas SOD2 knockdown abrogated the protective role of melatonin in hypoxic GCs. In conclusion, our study elucidates that melatonin, through MTNR1B activation, fosters SOD2 expression, effectively quelling mtROS-JNK-FOXO1-mediated apoptosis in follicular GCs under hypoxic stress.

Accumulations of high molecular weight glutenin subunits (HMW‐GS) and glutenin macropolymer (GMP) in wheat grains are important indicators of grain quality. Two wheat cultivars, Yangmai 158 (shading tolerant) and Yangmai 11 (shading intolerant) which contains the same subunit pairs of 7 + 8 and 2 + 12, were used to evaluate the impacts of shading on HMW‐GS accumulation and GMP concentration in the grain. Three shading levels were implemented from jointing to maturity, i.e. S1, S2 and S3, in which the plants received 8 %, 15 % and 23 % less radiation of the control (S0), respectively. The initial formation of HMW‐GS was pre‐dated by shading. The rapid HMW‐GS accumulation duration was shortened, and the accumulation rate during late grain filling period was lowered in the two relatively severe shaded treatments (S2 & S3). Thus, the total HMW‐GS accumulation in single grain at maturity was lower in S2 and S3 than in the control (S0). However, concentrations of HMW‐GS and GMP at maturity increased because of the reduced single grain weight in S2 and S3, as compared to S0. In contrast, the low density shading (S1) prolonged the rapid accumulation duration of HMW‐GS, hence increased the accumulation and concentration of HMW‐GS in the grains. Consequently, S1 reduced falling number and SDS‐sedimentation volume, while shortened dough development time (DDT) and dough stability time (DST). In contrast, S2 and S3 increased falling number, wet‐gluten concentration and SDS‐sedimentation volume, and lengthened the DDT and DST. In addition, the fluctuations in accumulations of HMW‐GS and GMP and most quality traits because of shading in Yangmai 158 were less than Yangmai 11. The interrelations between HMW‐GS accumulation, GMP concentration and quality of grain and dough were further discussed.