Inhibition of the human colonic thiamine pyrophosphate (TPP) uptake process by the pro‐inflammatory cytokine, TNF‐α and IFN‐γ

Abstract

Thiamin in its pyrophosphate form, i. e., thiamin pyrophosphate (TPP), is essential for normal cellular functions due to its involvement in energy metabolism, maintenance of normal cellular redox state, and mitochondrial structure/function. Humans and other mammals obtain thiamin through intestinal absorption, as they lack the ability to synthesize the vitamin de novo. The vitamin is obtained from both dietary and microbiota sources. A considerable amount of the vitamin provided by the later source exists in the form of TPP. We have previously shown the existence of a specific and high‐affinity carrier‐mediated uptake process for TPP in human colonocytes (Am J Physiol Gastrointest Liver Physiol. 2012; 303: G389–95) and determined the molecular identity of the system involved (product of the SLC44A4 gene) (J Biol Chem. 2014; 289: 4405–16). We have also cloned the promoter of the SLC44A4 gene and delineated certain aspects of its transcriptional and post‐transcrptional regulation (Am J Physiol Cell Physiol 308: C750–C757, 2015; Am J Physiol cell Physiol. 2017; ajpcell.00169.2017). Pro‐inflammatory cytokines tumor necrosis factor‐α (TNF‐α) and interferon‐γ (IFN‐ γ) are involved in the pathogenesis of inflammatory bowel diseases and has been shown to affect transport physiology of a variety of substrates. The effect of prolonged‐exposure of colonic epithelial cells to TNF‐α and IFN‐ γ on uptake of TPP has not been examined and was investigated in this study. The results showed that exposing the human‐derived colonic epithelial NCM460 cells to clinically relevant concentration of TNF‐α (20 ng/ml for 48hr) and IFN‐ γ (30 ng/ml for 48 hrs) leads to a significant (p < 0.01) inhibition in carrier‐mediated TPP uptake. This was associated with a significant reduction in the level of the expression of SLC44A4 protein, mRNA and hetronuclear RNA (hnRNA) levels, as well as in a significant inhibition in the activity of the SLC44A4 promoter. We also observed a significant decrease in the expression of the transcription factor ELF3 (which drive the SLC44A4 promoter) following exposure to TNF‐α and IFN‐ γ. Studies are in progress to understand the exact molecular mechanism involved in this process. This study for the first time provide clear evidence that exposure of human‐derived colonic epithelial NCM460 cells to TNF‐ α and IFN‐ γ negatively affect the colonic TPP transport, and that the effect is mediated at the level of transcription of the SLC44A4 gene.Support or Funding InformationSupported by grants from the DVA and the NIH (DK‐56061, DK58057, and AA 018071)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.