Erythropoietin reduces nerve demyelination, neuropathic pain behavior and microglial MAPKs activation through erythropoietin receptors on Schwann cells in a rat model of peripheral neuropathy

Abstract

Neuroprotective effects of erythropoietin (EPO) on peripheral nerve injury remain uncertain. This study investigated the efficacy of EPO in attenuating median nerve chronic constriction injury (CCI)‐induced neuropathy. Animals received an intraneural injection of EPO at doses of 1,000, 3,000, or 5,000 units/kg 15 min before median nerve CCI. Afterwards, the behavioral and electrophysiological tests were conducted. Immunohistochemistry and immunoblotting were used for qualitative and quantitative analysis of microglial and mitogen‐activated protein kinases (MAPKs), including p38, JNK, and ERK, activation. Enzyme‐linked immunosorbent assay and microdialysis were applied to measure pro‐inflammatory cytokine and glutamate responses, respectively. EPO pre‐treatment dose‐dependently ameliorated neuropathic pain behavior, decreased microglial and MAPKs activation, and diminished the release of pro‐inflammatory cytokines and glutamate in the ipsilateral cuneate nucleus after CCI. Moreover, EPO pre‐treatment preserved myelination of the injured median nerve on morphological investigation and suppressed injury‐induced discharges. We also observed that EPO receptor (EPOR) expression was up‐regulated in the injured nerve after CCI. Double immunofluorescence showed that EPOR was localized to Schwann cells. Furthermore, siRNA‐mediated knockdown of EPOR expression eliminated the therapeutic effects of EPO on attenuating the microglial and MAPKs activation, pro‐inflammatory cytokine responses, injury discharges, and neuropathic pain behavior in CCI rats. In conclusion, binding of EPO to its receptors on Schwann cells maintains myelin integrity and blocks ectopic discharges in the injured median nerve, that in the end contribute to attenuation of neuropathic pain via reducing glutamate release from primary afferents and inhibiting activation of microglial MAPKs and production of pro‐inflammatory cytokines.

X-ray induces mechanical and heat allodynia in mouse via TRPA1 and TRPV1 activation

“…MAPK, including ERK, JNK, and p38, is required to maintain allodynia under inflammatory pain, 58 and inhibition of MAPK could reduce neuropathic pain. 59 In this study, both of pJNK and pERK were significantly increased in skin, SN, and DRG. These data suggested that MAPK pathway was involved in X-ray-induced allodynia.…”

The Role of PI3K/AKT and MAPK Signaling Pathways in Erythropoietin Signalization

“…Recently, the MAPK/ERK pathway was identified as a downstream effector of the EPO signaling pathway for migration and positioning of neurons in the developing neocortex [ 82 , 83 ]. On the contrary, in Schwann cells, EPO inhibited the microglial MAPK pathway to maintain myelin integrity [ 84 ]. Indeed, the neuroprotective effect of the ERK pathway is associated with either its activation [ 85 ] or inhibition [ 86 ] and depends on factors such as cell lineage, culture environment, and pathological circumstances.…”

Obligatory role of Schwann cell‐specific erythropoietin receptors in erythropoietin‐induced functional recovery and neurogenic muscle atrophy after nerve injury

“…Experimental and clinical studies have demonstrated that EPO can function as a neuroprotective molecule by mediating angiogenesis and mitigating oxidative stress, inflammation, and apoptosis 18‐22 . Despite potent neuroprotective effects of EPO in rodent models of PNI, 5,7‐11 investigation into the functional role of EpoR under baseline conditions or with exogenous EPO was not possible because of embryonic lethality of global EPO null and EpoR null mice 23,24 and the lack of selective EpoR antagonists or mice lacking Schwann cell‐specific EpoR . Although we demonstrated that EPO‐induced increased EpoR expression in the crushed nerves of mice was associated with improved functional recovery, 5 the specificity of the EpoR antibody is debatable 25,26 .…”

“…EPO has both direct and indirect effects on nerve cells and EPO's role as a neuroprotective agent is multifactorial 1‐4 . EPO treatment: (a) enhances global functional recovery of the affected limb, (b) promotes remyelination of the injured nerve, and (c) improves nerve conduction velocity in rodent model of traumatic peripheral nerve injury (PNI) 5,7‐11 . Nevertheless, the physiological role of EpoR in PNI recovery remains uncertain mainly because of the lack of selective EpoR antagonists or a Schwann cell‐specific EpoR deletion animal model.…”