Effects of Physiological Temperature Changes On Micro RNA Expression and Their Functional Consequences

Abstract

Physiological changes in human core body temperature have important biological consequences for host response to infection, inflammation and survival. Work from our lab and others have shown that changes in temperature within clinically relevant range modify the expression of many chemokines, cytokines and other signaling molecules. Previous studies have focused on transcriptional regulation of temperature-dependent gene expression. In our present studies, we analyzed the mechanisms of temperature-dependent post transcriptional gene regulation by small non coding RNAs called micro RNAs (miRNAs). We found that exposure to clinically relevant hypothermia (32°C) within physiological range increased the expression of a surprisingly limited subset of miRNAs with some unusual characteristics. These miRNAs represent the passenger strands of miRNA duplex that are usually less abundant at 37°C. The same miRNAs tended to decrease at 39.5°C. Three of these miRNA targeted protein kinase C alpha (PKCα), a key player in cell cycle regulation. PKCα protein levels decreased with temperature and were rescued by miRNA inhibition at 32°C. The PKCα-dependent block of G1-S cell cycle transition was reversed at 32°C, and the effects of 32°C abrogated by miRNA inhibition. We further studied the effects of physiological temperature change on wnt signaling pathway, which contains several predicted targets of temperature-sensitive miRNAs. Exposure to 32°C reduced and exposure to 39.5°C increased wnt signaling as measured by wnt-dependent gene expression and a wnt-dependent reporter plasmid. Hypothermia reduced cell levels of the wnt-dependent transcription factor, TCF7 and this was reversed by miRNA inhibitors. The potential impact of these temperature changes on lung injury, repair, and fibrosis was evaluated by analyzing expression of genes involved in epithelial mesenchymal transition, which were reduced at 32°C and increased at 39.5°C. These genes, including collagen-1, TWIST1, N-cadherin, and MMP7 have all been shown to markers of human lung fibrosing diseases. These studies suggest that fever may worsen and hypothermia mitigate lung fibrosis and identifies a set of temperature-sensitive miRNAs as one potential mechanism.