Increased cerebral expressions of MMPs, CLDN5, OCLN, ZO1 and AQPs are associated with brain edema following fatal heat stroke

Human brain samples were collected from 46 autopsy cases, including 23 fatal heat stroke cases and 23 age-matched controls. Nine candidate reference genes (PES1, POLR2A, IPO8, HMBS, SDHA, GAPDH, UBC, B2M, ACTB) were evaluated in the cerebral cortex of 10 forensic autopsy cases (5 heat stroke and 5 controls), using the geNorm module in qBase(plus) software. SDHA, POLR2A, IPO8 and HMBS were identified as the most stable reference genes. Using these validated reference genes, mRNA expressions of Matrix metalloproteinases (MMPs, MMP2 and MMP9), Claudin5 (CLDN5), Occludin (OCLN), Zona occludens protein-1 (ZO1) and Aquaporins (AQPs, AQP1 and AQP4) in the cerebral cortex were examined. Relative mRNA quantification using Taqman real-time PCR assay demonstrated increased calibrated normalized relative quantity (CNRQ) values of MMP9, CLDN5, OCLN, ZO1 and AQP4 in heat stroke cases. Heat stroke cases showed an increase in brain water content, which was found to be positively correlated with MMP9, OCLN, ZO1 and CLDN5 mRNA. When using one conventional reference gene (GAPDH or ACTB) for normalization, no difference was detected between heat stroke and controls. In immunostaining, only AQP4 showed more intense staining in most heat stroke cases. The present study, for the first time, reports increased cerebral MMP9, CLDN5, OCLN, ZO1 and AQP4 in heat stroke and suggest a crucial role of reference gene selection when using postmortem human tissues.