Differential roles of Aβ processing in hypoxia-induced axonal damage

Non-prophylactic resveratrol-mediated protection of neurite integrity under chronic hypoxia is associated with reduction of Cav1.2 channel expression and calcium overloading

Cellular hypoxia is a major cause of oxidative stress, culminating in neuronal damage in neurodegenerative diseases. Numerous ex vivo studies have implicated that hypoxia episodes leading to disruption of Ca²⁺ homeostasis and redox status contribute to the progression of various neuropathologies and cell death. Isolation and maintenance of primary cell culture being cost-intensive, the details of the time course relationship between Ca²⁺ overload, L-type Ca²⁺ channel function, and neurite retraction under chronic and long-term hypoxia remain undefined. In order to explore the effect of oxidative stress and Ca²⁺ overload on neurite length, first, we developed a 5-day-long neurite outgrowth model using N2a cell line. Second, we propose a chronic hypoxia model to investigate the modulation of the L-type Ca²⁺ channel (Cav1.2) and oxidative resistance gene (OXR1) expression level during the process of neurite retraction and neuronal damage over 32 h. Thirdly, we developed a framework for quantitative analysis of cytosolic Ca²⁺, superoxide formation, neurite length, and constriction formation in individual cells using live imaging that provides an understanding of molecular targets. Our findings suggest that an increase in cytosolic Ca²⁺ is a feature of an early phase of hypoxic stress. Further, we demonstrate that augmentation in the L-type channel leads to amplification in Ca²⁺ overload, ROS accumulation, and a reduction in neurite length during the late phase of hypoxic stress. Next, we demonstrated that non-prophylactic treatment of resveratrol leads to the reduction of calcium overloading under chronic hypoxia via lowering of L-type channel expression. Finally, we demonstrate that resveratrol-mediated reduction of Cav1.2 channel and STAT3 expression are associated with retention of neurite integrity. The proposed in vitro model assumes significance in the context of drug designing and testing that demands monitoring of neurite length and constriction formations by imaging before animal testing.

Dehydroepiandrosterone alleviates hypoxia-induced learning and memory dysfunction by maintaining synaptic homeostasis

AIMS

Hypoxia causes plenty of pathologies in the central nervous system (CNS) including impairment of cognitive and memory function. Dehydroepiandrosterone (DHEA) has been proved to have therapeutic effects on CNS injuries by maintaining the homeostasis of synapses, yet its effect on hypoxia-induced CNS damage remains unknown.

METHODS

In vivo and in vitro models were established. Concentrations of glutamate and γ GABA were tested by ELISA. Levels of synapse-associated proteins were measured by western blotting. Density of dendritic protrusions of hippocampal neurons was assessed by Golgi staining. Immunofluorescence was adopted to observe the morphology of primary neurons. The novel object recognition test (NORT) and shuttle box test were used to evaluate cognition.

RESULTS

Dehydroepiandrosterone reversed abnormal elevation of glutamate levels, shortenings of neuronal processes, decreases in the density of dendritic protrusions, downregulation of synaptosome-associated protein (SNAP25), and impaired cognition caused by hypoxia. Hypoxia also resulted in notably downregulation of syntaxin 1A (Stx-1A). Overexpression of Stx-1A dramatically attenuated hypoxia-induced elevation of glutamate. Treatment with DHEA reversed the Stx-1A downregulation caused by hypoxic exposure.

CONCLUSION

Dehydroepiandrosterone may exert a protective effect on hypoxia-induced memory impairment by maintaining synaptic homeostasis. These findings offer a novel understanding of the therapeutic effect of DHEA on hypoxia-induced cognitive dysfunction.

Emerging Roles of Dyslipidemia and Hyperglycemia in Diabetic Retinopathy: Molecular Mechanisms and Clinical Perspectives

Diabetic retinopathy (DR) is a significant cause of vision loss and a research subject that is constantly being explored for new mechanisms of damage and potential therapeutic options. There are many mechanisms and pathways that provide numerous options for therapeutic interventions to halt disease progression. The purpose of the present literature review is to explore both basic science research and clinical research for proposed mechanisms of damage in diabetic retinopathy to understand the role of triglyceride and cholesterol dysmetabolism in DR progression. This review delineates mechanisms of damage secondary to triglyceride and cholesterol dysmetabolism vs. mechanisms secondary to diabetes to add clarity to the pathogenesis behind each proposed mechanism. We then analyze mechanisms utilized by both triglyceride and cholesterol dysmetabolism and diabetes to elucidate the synergistic, additive, and common mechanisms of damage in diabetic retinopathy. Gathering this research adds clarity to the role dyslipidemia has in DR and an evaluation of the current peer-reviewed basic science and clinical evidence provides a basis to discern new potential therapeutic targets.

The Roles of Microtubules and Membrane Tension in Axonal Beading, Retraction, and Atrophy

Axonal beading, or the formation of a series of swellings along the axon, and retraction are commonly observed shape transformations that precede axonal atrophy in Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions. The mechanisms driving these morphological transformations are poorly understood. Here, we report controlled experiments that can induce either beading or retraction and follow the time evolution of these responses. By making quantitative analysis of the shape modes under different conditions, measurement of membrane tension, and using theoretical considerations, we argue that membrane tension is the main driving force that pushes cytosol out of the axon when microtubules are degraded, causing axonal thinning. Under pharmacological perturbation, atrophy is always retrograde, and this is set by a gradient in the microtubule stability. The nature of microtubule depolymerization dictates the type of shape transformation, vis-à-vis beading or retraction. Elucidating the mechanisms of these shape transformations may facilitate development of strategies to prevent or arrest axonal atrophy due to neurodegenerative conditions.