Profiling the Hsp70 Chaperone Network in Heat-Induced Proteotoxic Stress Models of Human Neurons

SIMPLE SUMMARY: Rising temperatures and consequent heat waves are detrimental manifestations of climate change for the population’s health. Exposure to extreme environmental heat during episodes of intense and long-lasting heat waves is a direct cause of heat-related illnesses, particularly life-threatening heat stroke. A harmful manifestation of heat stroke is damage to the central nervous system, particularly the brain, which can result in permanent disability in approximately a third of patients. Heat can damage biomolecules, particularly proteins, because of their high vulnerability to changes in cellular conditions such as temperature. Temperature-induced protein damage leads to misfolding and clumping into aggregates that are the neurotoxic agents for most neurodegenerative disorders, including heat-induced damage, with certain defining features for later. The cellular response to these processes is to increase the production of a subset of helpful proteins called heat shock proteins 70 (Hsp70). Here, we report that hyperthermia induces severe brain proteotoxic stress in different neuronal models. Likewise, we showed a differential vulnerability among neuronal cells, with more damage in mature than young cells. As part of the stress response, we report the identification, differential importance, and co-expression of Hsp70 chaperones and their interacting partners in the human neuronal models of heat-induced damage. These findings support the idea that proteotoxic stress may play a role in heat stroke-induced brain damage. This study also helps expand our knowledge about stress response during neurodegenerative damage and is essential in developing therapeutic approaches. ABSTRACT: Heat stroke is among the most hazardous hyperthermia-related illnesses and an emerging threat to humans from climate change. Acute brain injury and long-lasting brain damage are the hallmarks of this condition. Hyperthermic neurological manifestations are remarkable for their damage correlation with stress amplitude and long-term persistence. Hyperthermia-induced protein unfolding, and nonspecific aggregation accumulation have neurotoxic effects and contribute to the pathogenesis of brain damage in heat stroke. Therefore, we generated heat-induced, dose-responsive extreme and mild proteotoxic stress models in medulloblastoma [Daoy] and neuroblastoma [SH-SY5Y] and differentiated SH-SY5Y neuronal cells. We show that heat-induced protein aggregation is associated with reduced cell proliferation and viability. Higher protein aggregation in differentiated neurons than in neuroblastoma precursors suggests a differential neuronal vulnerability to heat. We characterized the neuronal heat shock response through RT-PCR array analysis of eighty-four genes involved in protein folding and protein quality control (PQC). We identify seventeen significantly expressed genes, five of which are Hsp70 chaperones, and four of their known complementing function proteins. Protein expression analysis determined the individual differential contribution of the five Hsp70 chaperones to the proteotoxic stress response and the significance of only two members under mild conditions. The co-expression analysis reveals significantly high co-expression between the Hsp70 chaperones and their interacting partners. The findings of this study lend support to the hypothesis that hyperthermia-induced proteotoxicity may underlie the brain injury of heat stroke. Additionally, this study presents a comprehensive map of the Hsp70 network in these models with potential clinical and translational implications.