Age-Dependent Astroglial Vulnerability to Hypoxia and Glutamate: The Role for Erythropoietin

Abstract

Extracellular accumulation of toxic concentrations of glutamate (Glu) is a hallmark of many neurodegenerative diseases, often accompanied by hypoxia and impaired metabolism of this neuromediator. To address the question whether the multifunctional neuroprotective action of erythropoietin (EPO) extends to the regulation of extracellular Glu-level and is age-related, young and culture-aged rat astroglial primary cells (APC) were simultaneously treated with 1mM Glu and/or human recombinant EPO under normoxic and hypoxic conditions (NC and HC). EPO increased the Glu uptake by astrocytes under both NC and especially upon HC in culture-aged APC (by 60%). Moreover, treatment with EPO up-regulated the activity of glutamine synthetase (GS), the expression of glutamate-aspartate transporter (GLAST) and the level of EPO mRNA. EPO alleviated the Glu- and hypoxia-induced LDH release from astrocytes. These protective EPO effects were concentration-dependent and they were strongly intensified with age in culture. More than a 4-fold increase in apoptosis and a 2-fold decrease in GS enzyme activity was observed in APC transfected with EPO receptor (EPOR)-siRNA. Our in vivo data show decreased expression of EPO and a strong increase of EPOR in brain homogenates of APP/PS1 mice and their wild type controls during aging. Comparison of APP/PS1 and age-matched WT control mice revealed a stronger expression of EPOR but a weaker one of EPO in the Alzheimer’s disease (AD) model mice. Here we show for the first time the direct correlation between the extent of differentiation (age) of astrocytes and the efficacy of EPO in balancing extracellular glutamate clearance and metabolism in an in-vitro model of hypoxia and Glu-induced astroglial injury. The clinical relevance of EPO and EPOR as markers of brain cells vulnerability during aging and neurodegeneration is evidenced by remarkable changes in their expression levels in a transgenic model of AD and their WT controls.

Antifibrotic Effects of Amyloid-Beta and Its Loss in Cirrhotic Liver

“…Astroglia-rich primary cultures (APC) were prepared from newborn C57/BL6 (Charles River) mouse brains as described elsewhere [3,4,28]. Briefly, the cells obtained from 5-7 brains of newborn littermates were mechanically dissociated, centrifuged, and plated onto cell culture flasks (1 × 10 6 cells/75 cm 2 ) in DMEM with 4.5 g/L glucose supplemented with 10% fetal calf serum, 100 µg/mL streptomycin sulphate, 100 units/mL penicillin G, and 1 µM pyruvate (Biochrom AG, Berlin, Germany) in a humidified 10% CO 2 atmosphere at 37 • C.…”

Regeneration in the nervous system with erythropoietin

“…In relation to blocking the detrimental effects of oxidative stress and ROS, EPO protects endothelial cells (144, 194, 199, 203, 204, 214, 220, 221, 316, 368, 371–376), neurons (26, 210, 237, 345, 362, 377–382), astrocytes (377, 383–385), and microglia (166, 186, 196, 227, 368, 381). During oxidative stress, EPO also preserves neurogenesis (336, 386), stem cell development (126, 220, 237, 312, 372, 387), and promotes erythroid progenitor cell development with the modulation of FoxO3a activity (29, 169, 237, 307).…”

Erythropoietin and mTOR: A “One-Two Punch” for Aging-Related Disorders Accompanied by Enhanced Life Expectancy

“…EPO has the capacity to offer protection against a number of disease entities (208–212) as well as enhanced biological activity (213, 214). For example, EPO has been reported to improve clinical outcome during development (215), neurodegenerative disorders (216), stroke (217–222), aging (223), TBI (32, 224), vascular disease (217–222), depression (208, 225), and metabolic disturbances (63, 211, 226, 227). …”