Hypoxia inducible factors HIFs including HIF HIF HIF and HIF
Hypoxia-inducible factors (HIFs), including HIF-1α, HIF-1β, HIF-2α and HIF-3α, are important endogenous signaling proteins that contribute to the cellular response to hypoxia. Among these proteins, HIF-1α is involved in many pathophysiological processes, including inflammation, tumor growth and metastasis, angiogenesis, hypoxic injury, neuronal apoptosis and stem cell proliferation and differentiation. Interestingly, many of these mechanisms are similar to the pathogenesis of epilepsy. Recent studies have demonstrated that HIF-1α is upregulated in the pathological hippocampus of patients suffering from temporal lobe epilepsy and animal models (Feast et al., 2012, Gualtieri et al., 2013), indicating that HIF-1α is involved in the hippocampal pathological changes observed after epilepsy. Although previous studies have shown that HIF may have an important effect on regulating vascular endothelial growth factor (VEGF) (Huang et al., 2010), erythropoietin (EPO) (Fan et al., 2009) production, the tumor necrosis factor (TNF-α) pathway (Yang et al., 2016) and hippocampal apoptosis (Long et al., 2014) during the process of epilepsy, the specific mechanism by which HIF-1α regulates epilepsy remains unclear.
Notch signaling is an evolutionarily conserved signaling pathway involved in various cellular processes in adult tissues. As one of the most important pathways, Notch signaling is activated by ligand binding and releasing the Notch intracellular domain (NICD), which transports into the nucleus and binds the DNA-binding transcription factor CSL (Kopan and Ilagan, 2009). The aberrant activation of Notch signaling has been identified in multiple diseases, including different types of tumors (Ranganathan et al., 2011), vascular diseases (Cheng et al., 2014) and epilepsy (Sha et al., 2014). Moreover, Notch is a critical modulator promoting the proliferation and differentiation of neural stem Beauvericin synthesis into astrocytes and plays an important role in the maintenance of dendritic morphology (Breunig et al., 2007), which is strongly related to the mechanism of epilepsy. Additionally, Sha et al. found that Notch signaling is upregulated in response to seizure activity, and its activation further promotes neuronal excitation in acute seizures (Sha et al., 2014). Whether activated Notch signaling is involved in the aberrant neurogenesis observed in acute epilepsy needs further investigation.
Recent studies have shown that HIF-1α regulates the maintenance and progression of several diseases by activating Notch1 signaling (Qiang et al., 2012). Additionally, HIF-1α promotes the metastasis and invasion of tumor cells by binding NICD and stabilizing its structure (Sahlgren et al., 2008). However, whether HIF-1α is related to epilepsy through Notch signaling remains unclear. Thus, we investigated the role of HIF-1α in neurogenesis and whether Notch signaling is involved in this process during epileptogenesis by assessing hippocampal apoptosis, neuronal injury, and the proliferation and differentiation of neural stem cells (NSCs) in four groups, including the control, epilepsy, epilepsy + 2-methoxyestradiol (2ME2) and epilepsy + GSI-IX (DAPT) groups. Our results suggested that HIF-1α could mediate neurogenesis through the Notch signaling pathway in lithium chloride- and pilocarpine-induced temporal lobe epilepsy, illustrating the mechanism of HIF and Notch during the process of epileptic neurogenesis. These findings might be highly significant for exploring how epilepsy occurs and may provide new targets for medicinal development.
Introduction Pathological cardiac hypertrophy is an adaptive response of the heart to sustained pressure overload. With the development of cardiac hypertrophy, myocardial energy metabolism may gradually switch from fatty acids to glucose utilization (Tuomainen and Tavi, 2017). The hypoxia-inducible factor-1α (HIF-1α) may play an important role in this shift process (Abe et al., 2017), its activation can affect the expressions of peroxisome proliferator activated receptor α/γ (PPARα/γ) (Krishnan et al., 2009, Narravula and Colgan, 2001), which are known to regulate the homeostasis of myocardial energy metabolism. PPARα is a key regulator of myocardial fatty acid uptake and oxidation, and it can activate the carnitine palmitoyltransferase-1 (CPT-1), which is responsible for transporting fatty acids from the cytosol into the mitochondria for subsequent β-oxidation (Lehman and Kelly, 2002). PPARα can also control the pyruvate dehydrogenase kinase-4 (PDK-4), a negative regulating enzyme in myocardial glucose oxidation process (Liao et al., 2017). PPARγ can increase the expressions of glucose transporter-4 (GLUT-4) and glycerol phosphate acyltransferase (GPAT) (Chabowski et al., 2012, Mueckler and Thorens, 2013). The former may promote the uptake and transport of glucose from the blood into the myocardium, and the latter can increase the myocardial triglyceride biosynthesis. Thus, HIF-1α-mediated abnormal expressions of PPARα/γ may result in the imbalance of myocardial energy metabolism.