Erythropoietin Requires NF-κB and its Nuclear Translocation to Prevent Early and Late Apoptotic Neuronal Injury During β-Amyloid Toxicity

Abstract

No longer considered exclusive for the function of the hematopoietic system, erythropoietin (EPO) is now considered as a viable agent to address central nervous system injury in a variety of cellular systems that involve neuronal, vascular, and inflammatory cells. Yet, it remains unclear whether the protective capacity of EPO may be effective for chronic neurodegenerative disorders such as Alzheimer's disease (AD) that involve beta-amyloid (Abeta) apoptotic injury to hippocampal neurons. We therefore investigated whether EPO could prevent both early and late apoptotic injury during Abeta exposure in primary hippocampal neurons and assessed potential cellular pathways responsible for this protection. Primary hippocampal neuronal injury was evaluated by trypan blue dye exclusion, DNA fragmentation, membrane phosphatidylserine (PS) exposure, and nuclear factor-kappaB (NF-kappaB) expression with subcellular translocation. We show that EPO, in a concentration specific manner, is able to prevent the loss of both apoptotic genomic DNA integrity and cellular membrane asymmetry during Abeta exposure. This blockade of Abeta generated neuronal apoptosis by EPO is both necessary and sufficient, since protection by EPO is completely abolished by co-treatment with an anti-EPO neutralizing antibody. Furthermore, neuroprotection by EPO is closely linked to the expression of NF-kappaB p65 by preventing the degradation of this protein by Abeta and fostering the subcellular translocation of NF-kappaB p65 from the cytoplasm to the nucleus to allow the initiation of an anti-apoptotic program. In addition, EPO intimately relies upon NF-kappaB p65 to promote neuronal survival, since gene silencing of NF-kappaB p65 by RNA interference removes the protective capacity of EPO during Abeta exposure. Our work illustrates that EPO is an effective entity at the neuronal cellular level against Abeta toxicity and requires the close modulation of the NF-kappaB p65 pathway, suggesting that either EPO or NF-kappaB may be used as future potential therapeutic strategies for the management of chronic neurodegenerative disorders, such as AD.

Erythropoietin ameliorates chemotherapy‐induced fibrosis of the lungs in a preclinical murine model

“…25,44 Although there is controversy as to whether EPO exerts a direct or indirect effect on the production of pro-inflammatory proteins, such as TNF-a and IL-1, convincing evidence exists to suggest that EPO may block the activity and perhaps downregulate expression of these proteins in experimental models. 45,46 Therefore, our findings are consistent with the aforementioned studies and confirm the ability of administered EPO to attenuate inflammatory responses in pulmonary tissue in a bleomycin-animal model.…”

“…Whether this effect of EPO is direct via cellular pathways involving inflammatory transcription factors (such as NF-kB) or indirect through inhibition of ROS formation and cytokine production remains to be seen. 44,46,52 Also, it is not clear from the present data whether EPO affects early or late fibrosis. Studies are underway in our laboratory to address these questions.…”

Triple play: Promoting neurovascular longevity with nicotinamide, WNT, and erythropoietin in diabetes mellitus

“…Phosphorylation of Akt leads to its activation and protects cells against genomic DNA degradation and membrane PS exposure [45,61,105]. Up-regulation of Akt activity during multiple injury paradigms, such as vascular and cardiomyocyte ischemia [106,107], free radical exposure [45,108], N-methyl-D-aspartate toxicity [109], hypoxia [110,111], β-amyloid toxicity [112][113][114], DNA damage [31, 41,110,115], metabotropic receptor signaling [38,116,117], cell metabolic pathways [42,63], and oxidative stress [31,33,41] increases cell survival. Cytoprotection through Akt also can involve control of inflammatory cell activation [33, 41,61], transcription factor regulation [118], maintenance of mitochondrial membrane potential (ΔΨ m ), prevention of cytochrome c release [45,61,105], and blockade of caspase activity [45,61,110] In addition to targeting the activity of membrane PS exposure and microglial activation, nicotinamide inhibits several pro-inflammatory cytokines, such as interleukin-1β, interleukin-6, interleukin-8, tissue factor, and tumor necrosis factor-α (TNF-α) [119][120][121][122].…”

“…In cells that involve the brain or the retina, EPO can prevent injury from hypoxic ischemia [45,110,[225][226][227], excitotoxicity [228,229], infection [230], free radical exposure [61, 105,229], amyloid exposure [112], staurosporine [231], and dopaminergic cell injury [232]. In addition, administration of EPO also represents a viable option for the prevention of retinal cell injury during glutamate toxicity [233] and glaucoma [234].…”

“…Dependent upon Akt controlled pathways, the transactivation domain of the p65 subunit of NF-κB is activated by IKK and the IKKκ catalytic subunit to lead to the induction of protective anti-apoptotic pathways [264]. Increased expression of NF-κB during injury can occur in cells, such as in inflammatory microglial cells [32,112,265] and in neurons [266]. NF-κB represents a critical pathway that is responsible for the activation of inhibitors of apoptotic proteins (IAPs), the maintenance of Bcl-x L expression, [27,267], and protection against cell injury during oxidative stress [112].…”