Role of hif-1a in thiamine deficiency
Zera, Kristy Anne
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Chronic alcohol consumption is one of the leading causes of preventable death in the United States. Alcohol misuse leads to alcohol-associated dementia and results in cognitive deficits due to oxidative stress, inflammation and excitotoxicity in the brain. Thiamine deficiency is a common comorbidity of alcohol abuse, which leads to mitochondrial dysfunction and subsequent oxidative stress, inflammation and excitotoxicity independent of ethanol consumption. These changes result in biochemical lesions in focal brain regions with subsequent apoptotic cell death. However, the underlying factor responsible for the initiation of damage is unresolved. We have previously demonstrated that thiamine deficiency stabilizes and activates the hypoxia inducible transcription factor HIF-1α under physiological oxygen levels. Under acute ischemic stress, HIF-1α is responsible for metabolic reprogramming to promote a shift towards glycolytic metabolism and subsequent decrease in oxygen utilization. This allows cellular adaptation and survival in low oxygen conditions. Additionally, under chronic ischemic stress HIF-1α may promote the activation of pro-inflammatory and pro-apoptotic proteins, resulting in cell death. The role of HIF-1α in thiamine deficiency is unclear, however the activation of HIF-1α in both conditions suggests a congruent transcriptional response to both stress conditions. Therefore, the purpose of this research is to understand the role of HIF-1α activation in thiamine deficiency. Using a HIF-1α transcription factor assay and chromatin immunoprecipitation assay in breast and colon cancer cell models, we have identified the thiamine transporter SLC19A3 as a direct transcriptional target of HIF-1α in both hypoxia and thiamine deficiency. Additionally, we report HIF-1α activation in mouse primary astrocytes exposed to thiamine deficiency up to 2 weeks, and subsequent trans-activation of pro-apoptotic and pro-inflammatory HIF-1α target genes in these conditions resulting in apoptotic cell death. Using a pharmacological inhibitor of HIF-1α or thiamine repletion strategies, we reported a decrease in expression of pro-apoptotic target genes, and subsequent decrease in apoptotic cell death. Additionally, we observed that in vivo thiamine deficiency results in focal thalamic expression of HIF-1α and pro-apoptotic and pro-inflammatory target genes. To understand the mechanism of HIF-1α stabilization in thiamine deficiency, we investigated the activation of the PI3K/Akt pathway and accumulation of pyruvate and lactate in thiamine deficiency. We reported no role for Akt in thiamine deficiency-induced HIF-1α accumulation, although we did observe a correlation between pyruvate accumulation and HIF-1α stabilization in thiamine deficiency. Overall, these results suggest that HIF-1α activity in the thiamine deficient brain may contribute to focal apoptotic cell death and subsequent neurological symptoms associated with this condition.