1 2 3 4 Attenuated Thermoregulatory , Metabolic and Liver Acute Phase Protein Response to 5 Heat Stroke in TNF Receptor Knockout Mice

40 Tumor necrosis factor (TNF) is considered an adverse mediator of heat stroke (HS) based 41 on clinical studies showing high serum levels. However, soluble TNF receptors (sTNFR; TNF 42 antagonists) were higher in survivors than nonsurvivors and TNFR KO mice showed a trend 43 towards increased mortality suggesting TNF has protective actions for recovery. We delineated 44 TNF actions in HS by comparing thermoregulatory, metabolic and inflammatory responses 45 between B6129F2 (WT) and TNFR KO mice. Prior to heat exposure, TNFR KO mice showed 46 ~0.4°C lower core temperature (Tc; radiotelemetry), ~10% lower metabolic rate (Mr; indirect 47 calorimetry) and reduced plasma IL-1α and sIL-1RI than WT mice. KO mice selected warmer 48 temperatures than WT mice in a gradient, but remained hypothermic. In the calorimeter, both 49 genotypes showed a similar heating rate, but TNFR KO maintained lower Tc and Mr than WT 50 mice for a given heat exposure duration and required ~30 min longer to reach maximum Tc 51 (42.4°C). Plasma IL-6 increased at ~3h of recovery in both genotypes, but KO mice showed a 52 more robust sIL-6R response. Higher sIL-6R in the KO mice was associated with delayed liver 53 p-STAT3 protein expression and attenuated serum amyloid A3 (SAA3) gene expression 54 suggesting the acute phase response (APR) was attenuated in these mice. Our data suggest that 55 the absence of TNF signaling induced a regulated hypothermic state in the KO mice, TNF-IL-1 56 interactions may modulate Tc and Mr during homeostatic conditions, and TNF modulates the 57 APR during HS recovery through interactions with the liver IL-6-STAT3 pathway of SAA3 58 regulation. 59