L-theanine alleviates heat stress via modulating the transcriptional regulation of Hsph1 by Hsf1

Strategies altering dietary nutrients composition, such as the addition of appropriate essential amino acids or phytochemicals, is effective in addressing the adverse effects of heat stress (HS) under rising temperatures. The new food ingredient L-theanine (LTA), a natural non-protein amino acid found in tea, shows promising effect in alleviating HS. However, systematic studies underlying LTA mitigating HS are lacking. Here, we evaluated the mechanisms by which LTA alleviates HS both in vivo and in vitro. The results showed that LTA suppressed HS-induced decreases in cell viability, antioxidant enzyme activity, mitochondrial membrane potential and ATP content. It reduced reactive oxygen species levels and apoptosis in heat-stressed BRL-3A cells. In addition, LTA affected the expression of heat shock proteins, ribosomal proteins and apoptosis-relate genes during HS and HS recovery process. Similar results were observed in heat-stressed rats. Mechanistically, the alleviating effect of LTA on HS may be mediated by heat shock factor 1 (Hsf1). Specifically, in the initiation of HS, LTA promoted the binding of Hsf1 to the promoter of heat shock protein family H member 1 (Hsph1), which facilitated Hsph1 transcription and accelerated the response to HS. Following the end of HS treatment, LTA repressed the expression of Hsph1, thus restoring intracellular homeostasis. Taken together, these results suggest that LTA is effective in regulating the transcription of Hsph1 via Hsf1, thereby mitigating HS-induced hepatic injury. This provides scientific evidence that drinking tea is helpful in preventing HS and LTA is a promising anti-HS phytochemical deserves further development.