HSP70 reduces chronic hypoxia-induced neural suppression via regulating expression of syntaxin

Role of a Heat Shock Transcription Factor and the Major Heat Shock Protein Hsp70 in Memory Formation and Neuroprotection

Heat shock proteins (Hsps) represent the most evolutionarily ancient, conserved, and universal system for protecting cells and the whole body from various types of stress. Among Hsps, the group of proteins with a molecular weight of 70 kDa (Hsp70) plays a particularly important role. These proteins are molecular chaperones that restore the native conformation of partially denatured proteins after exposure to proteotoxic forms of stress and are critical for the folding and intracellular trafficking of de novo synthesized proteins under normal conditions. Hsp70s are expressed at high levels in the central nervous system (CNS) of various animals and protect neurons from various types of stress, including heat shock, hypoxia, and toxins. Numerous molecular and behavioral studies have indicated that Hsp70s expressed in the CNS are important for memory formation. These proteins contribute to the folding and transport of synaptic proteins, modulate signaling cascades associated with synaptic activation, and participate in mechanisms of neurotransmitter release. In addition, HSF1, a transcription factor that is activated under stress conditions and mediates Hsps transcription, is also involved in the transcription of genes encoding many synaptic proteins, whose levels are increased in neurons under stress and during memory formation. Thus, stress activates the molecular mechanisms of memory formation, thereby allowing animals to better remember and later avoid potentially dangerous stimuli. Finally, Hsp70 has significant protective potential in neurodegenerative diseases. Increasing the level of endogenous Hsp70 synthesis or injecting exogenous Hsp70 reduces neurodegeneration, stimulates neurogenesis, and restores memory in animal models of ischemia and Alzheimer’s disease. These findings allow us to consider recombinant Hsp70 and/or Hsp70 pharmacological inducers as potential drugs for use in the treatment of ischemic injury and neurodegenerative disorders.

Genetic Variation for Mitochondrial Function in the New Zealand Freshwater Snail Potamopyrgus antipodarum

The proteins responsible for mitochondrial function are encoded by 2 different genomes with distinct inheritance regimes, rendering rigorous inference of genotype-phenotype connections intractable for all but a few model systems. Asexual organisms provide a powerful means to address these challenges because offspring produced without recombination inherit both nuclear and mitochondrial genomes from a single parent. As such, these offspring inherit mitonuclear genotypes that are identical to the mitonuclear genotypes of their parents and siblings but different from those of other asexual lineages. Here, we compared mitochondrial function across distinct asexual lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail model for understanding the evolutionary consequences of asexuality. Our analyses revealed substantial phenotypic variation across asexual lineages at 3 levels of biological organization: mitogenomic, organellar, and organismal. These data demonstrate that different asexual lineages have different mitochondrial function phenotypes, likely reflecting heritable variation (i.e., the raw material for evolution) for mitochondrial function in P. antipodarum. The discovery of this variation combined with the methods developed here sets the stage to use P. antipodarum to study central evolutionary questions involving mitochondrial function, including whether mitochondrial mutation accumulation influences the maintenance of sexual reproduction in natural populations.

Heat shock protein 70 protects PC12 cells against ischemia-hypoxia/reoxygenation by maintaining intracellular Ca(2+) homeostasis

Heat shock protein 70 (HSP70) maintains Ca²⁺ homeostasis in PC12 cells, which may protect against apoptosis; however, the mechanisms of neuroprotection are unclear. Therefore, in this study, we examined Ca²⁺ levels in PC12 cells transfected with an exogenous lentiviral HSP70 gene expression construct, and we subsequently subjected the cells to ischemia-hypoxia/reoxygenation injury. HSP70 overexpression increased neuronal viability and ATPase activity, and it decreased cellular reactive oxygen species levels and intracellular Ca²⁺ concentration after hypoxia/reoxygenation. HSP70 overexpression enhanced the protein and mRNA expression levels of sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA), but it decreased the protein and mRNA levels of inositol 1,4,5-trisphosphate receptor (IP₃R), thereby leading to decreased intracellular Ca²⁺ concentration after ischemia-hypoxia/reoxygenation. These results suggest that exogenous HSP70 protects against ischemia-hypoxia/reoxygenation injury, at least in part, by maintaining cellular Ca²⁺ homeostasis, by upregulating SERCA expression and by downregulating IP₃R expression.

Heat shock response and homeostatic plasticity

Heat shock response and homeostatic plasticity are mechanisms that afford functional stability to cells in the face of stress. Each mechanism has been investigated independently, but the link between the two has not been extensively explored. We explore this link. The heat shock response enables cells to adapt to stresses such as high temperature, metabolic stress and reduced oxygen levels. This mechanism results from the production of heat shock proteins (HSPs) which maintain normal cellular functions by counteracting the misfolding of cellular proteins. Homeostatic plasticity enables neurons and their target cells to maintain their activity levels around their respective set points in the face of stress or disturbances. This mechanism results from the recruitment of adaptations at synaptic inputs, or at voltage-gated ion channels. In this perspective, we argue that heat shock triggers homeostatic plasticity through the production of HSPs. We also suggest that homeostatic plasticity is a form of neuroprotection.

Anti-hypoxia effect of adenovirus-mediated expression of heat shock protein 70 (HSP70) on primary cultured neurons

Heat shock protein 70 (HSP70) has attracted great attention recently in hypoxia injury because of its close link to the recovery after hypoxic-ischemic damage in organs. However, the cellular mechanism underlying its protective roles remains unclear. In this study, we developed a recombinant adenovirus containing HSP70-GFP (vAd-HSP70-GFP) and studied the effect of virus-mediated expression of exogenous HSP70 gene on neurons in response to hypoxia-reoxygenation injury. Virus-mediated expression of HSP70 was detected as early as 24 hr and lasted until 10 days after infection. Neurons with 48 hr vAd-HSP70-GFP infection were exposed to 0, 0.5, 1, 2, 3, or 4 hr hypoxia followed by 1 hr reoxygenation. The mRNA and protein levels of HSP70 in neurons exposed to different lengths of hypoxia were compared by using RT-PCR and Western blotting (WB). The 1-hr hypoxia exposure showed the most significant increases in the HSP70 mRNA and protein level compared with other exposure durations. MTT assay showed that HSP70 overexpression significantly increased the neuronal viability, accompanied by decreased lactate dehydrogenase (LDH) activity in the culture medium after hypoxia-reoxygenation. Neurons with vAd-HSP70-GFP exhibited increased levels of mitochondrial cytochrome C (Cyt-C) and decreased levels of cytoplasmic Cyt-C compared with vAd-GFP-infected cells. These results suggest a neuroprotective role of exogenous HSP70 against hypoxia-reoxygenation injury, possibly via preventing initiation of mitochondrial apoptosis.

Multifaceted role of heat shock protein 70 in neurons

Heat shock protein 70 (Hsp70) plays important roles in neural protection from stress by assisting cellular protein folding. In this review we discuss the current understanding of inducible and constitutive Hsp70 in maintaining and protecting neuronal synaptic function under normal and stressed conditions.