Identification of the Protective Role of DJ-1 in Hypoglycemic Astrocyte Injury Using Proteomics

Potential biomarkers in hypoglycemic brain injury

Oxidative stress is a major underlying mechanism in hypoglycemic brain injury. Several oxidative stress-related proteins were identified through previous proteomics and literature review. The aim of the present study was to evaluate the potential of these proteins as biomarkers in hypoglycemic brain injury. Forty male Sprague Dawley rats were randomly and equally divided into four groups: control, acute hypoglycemia, hypoglycemia resuscitation 24 h, and hypoglycemia resuscitation 7 days. The hypoglycemic brain injury rat model was successfully constructed according to the Auer model. Real-time fluorescent quantitative polymerase chain reaction, western blot analysis, and immunohistochemical staining were used to quantify the expression of oxidative stress-related proteins. We also verified the expression level of selected protein in the brain samples of fatal insulin overdose cases. The expression of oxidative stress-related proteins PEX1/5/12 was down-regulated in hypoglycemic brain injury (P < 0.05), while the expressions of DJ-1 and NDRG1 were up-regulated (P < 0.05). Compared with the control group, the serum oxidative stress indexes SOD and MDA in the acute hypoglycemia group were significantly different (P < 0.01). The expressions of DJ-1 and NDRG1 in the hippocampus, cortex, and hypothalamus of rats were increased (P < 0.05). The expressions of DJ-1 and NDRG1 proteins in the cortex of the autopsy samples of insulin overdose were increased (P < 0.05). Oxidative stress-related proteins showed potential value as specific molecular markers in hypoglycemic brain injury, but further confirmatory studies are needed.

Functional dissection of astrocyte-secreted proteins: Implications in brain health and diseases

Astrocytes, which are homeostatic cells of the central nervous system (CNS), display remarkable heterogeneity in their morphology and function. Besides their physical and metabolic support to neurons, astrocytes modulate the blood-brain barrier, regulate CNS synaptogenesis, guide axon pathfinding, maintain brain homeostasis, affect neuronal development and plasticity, and contribute to diverse neuropathologies via secreted proteins. The identification of astrocytic proteome and secretome profiles has provided new insights into the maintenance of neuronal health and survival, the pathogenesis of brain injury, and neurodegeneration. Recent advances in proteomics research have provided an excellent catalog of astrocyte-secreted proteins. This review categorizes astrocyte-secreted proteins and discusses evidence that astrocytes play a crucial role in neuronal activity and brain function. An in-depth understanding of astrocyte-secreted proteins and their pathways is pivotal for the development of novel strategies for restoring brain homeostasis, limiting brain injury/inflammation, counteracting neurodegeneration, and obtaining functional recovery.

DJ-1 overexpression restores ischaemic post-conditioning-mediated cardioprotection in diabetic rats: role of autophagy

IPO (ischaemic post-conditioning) is a promising method of alleviating myocardial IR (ischaemia-reperfusion) injury; however, IPO-mediated cardioprotection is lost in diabetic hearts via mechanisms that remain largely unclear. We hypothesized that decreased cardiac expression of DJ-1, a positive modulator of autophagy, compromises the effectiveness of IPO-induced cardioprotection in diabetic rats. Diabetic rats subjected to myocardial IR (30 min of coronary artery occlusion followed by 120 min of reperfusion) exhibited more severe myocardial injury, less cardiac autophagy, lower DJ-1 expression and AMPK (adenosine monophosphate-activated protein kinase)/mTOR (mammalian target of rapamycin) pathway activity than non-diabetic rats. IPO significantly attenuated myocardial injury and up-regulated cardiac DJ-1 expression, AMPK/mTOR activity and autophagy in non-diabetic rats but not in diabetic rats. AAV9 (adeno-associated virus 9)-mediated cardiac DJ-1 overexpression as well as pretreatment with the autophagy inducer rapamycin restored IPO-induced cardioprotection in diabetic rats, an effect accompanied by AMPK/mTOR activation and autophagy up-regulation. Combining HPO (hypoxic post-conditioning) with DJ-1 overexpression markedly attenuated HR (hypoxia-reoxygenation) injury in H9c2 cells with high glucose (HG, 30 mM) exposure, accompanied by AMPK/mTOR signalling activation and autophagy up-regulation. The DJ-1 overexpression-mediated preservation of HPO-induced cardioprotection was completely inhibited by the AMPK inhibitor compound C (CC) and the autophagy inhibitor 3-MA (3-methyladenine). Thus, decreased cardiac DJ-1 expression, which results in impaired AMPK/mTOR signalling and decreased autophagy, could be a major mechanism underlying the loss of IPO-induced cardioprotection in diabetes.

Protective effect of lithium chloride against hypoglycemia-induced apoptosis in neuronal PC12 cell

Hypoglycemia is defined by an arbitrary plasma glucose level lower than 3.9mmol/L and is a most common and feared adverse effect of treatment of diabetes mellitus. Emerging evidences demonstrated that hypoglycemia could induce enhanced apoptosis. Lithium chloride (LiCl), a FDA approved drug clinically used for treatment of bipolar disorders, is recently proven having neuroprotection against various stresses in the cellular and animal models of neural disorders. Here, we have established a hypoglycemia model in vitro and assessed the neuroprotective efficacy of LiCl against hypoglycemia-induced apoptosis and the underlying cellular and molecular mechanisms. Our studies showed that LiCl protects against hypoglycemia-induced neurotoxicity in vitro. Exposure to hypoglycemia results in enhanced apoptosis and the underlying cellular and molecular mechanisms involved inhibition of the canonical Wnt signaling pathway by decreasing wnt3a levels, β-catenin levels and increasing GSK-3β levels, which was confirmed by the use of Wnt-specific activator LiCl. Hypoglycemia-induced apoptosis were significantly reversed by LiCl, leading to increased cell survival. LiCl also alters the expression/levels of the Wnt pathway genes/proteins, which were reduced due to exposed to hypoglycemia. Overall, our results conclude that LiCl provides neuroprotection against hypoglycemia-induced apoptosis via activation of the canonical Wnt signaling pathway.