Vitamin B1 (thiamin) transport in Alzheimer’s Disease: Role of microRNAs in regulating level of expression of its transporters (SLC19A2 & SLC19A3) in human brain cells and effect of hypoxia

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PROJECT SUMMARY/ABSTRACT Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by Amyloid-β peptide-containing plaques, neurofibrillary tangles, neuronal loss in the brain, and cognitive deficits. Constant features of the disease include impaired glucose/energy metabolism, oxidative stress, and mitochondrial dysfunction in brain cells. Vitamin B1 (thiamin; also referred to as the “energy vitamin”) is indispensable for normal cellular function and metabolism. Thiamin serves as cofactor for multiple enzymes that are involved in critical metabolic reactions including oxidative energy metabolism, ATP production, and reduction of cellular oxidative stress; it also possesses anti-inflammatory properties. Thus, it is not surprising that cellular deficiency of thiamin leads to impairment in energy metabolism, reduction in cellular ATP level, and to a propensity for oxidative stress; it also leads to impairment in the function/structure of mitochondria. A wealth of evidence exist showing that vitamin B1 deficiency aggravates the pathology of AD, and that alterations in thiamine homeostasis/physiology occur in this neurodegenerative disease. The latter includes recently published findings from our laboratory showing that the level of expression of the cell membrane thiamin transporters-1 & -2 (THTR-1 & -2; products of the SLC19A2 and SLC19A3 genes) are significantly reduced in brain tissues of AD patients compared to control subjects. MicroRNAs (miRNAs) are a group of small noncoding single-stranded RNAs that exert gene-silencing effects. They regulate a variety of cellular functions including transport across cell membrane. Expression of miRNAs is tissue-specific; also effect of a miRNA on a target protein could be cell-specific in nature. In new preliminary studies, we obtained evidence suggesting that the level of expression of THTR-1 in human differentiated neuroblastoma SH-SY5Y cells is regulated by miRNAs (several of which have been shown to be induced in AD). In another preliminary study, we found that hypoxia (a condition that contributes to different pathological aspects of AD) causes significant inhibition in thiamin uptake and in level of expression of THTR-1 & -2 in human differentiated neuroblastoma SH-SY5Y cells. Based on these preliminary findings, we hypothesize in this supplement application that the level of expression of THTR-1 & -2 in brain cells is regulated by miRNAs, and that hypoxia exert deleterious effects on thiamin uptake physiology/molecular biology in these cells. We will test these hypotheses by accomplishing two specific aims: 1) Examine the role of miRNAs in regulating the level of expression of THTR-1 & -2 in human brain cells; and 2) Examine the effect of hypoxia on thiamin uptake by human brain cells and delineate the cellular/molecular mechanism(s) involved. We will use complementary models of human differentiated SH-SY5Ycells, human primary neurons, and human brain organoids in our investigations.