4B). == Figure 4. EPO-induced proregenerative effects in nerve cells are through EPO receptors and Janus kinase 2/Signal transducer and activator of transcription 5 pathway and not via early direct modulation of small GTPase RhoA. These preclinical studies indicate that EPO is a viable candidate drug to develop further for neuroprotection and enhancing nerve repair in patients with GBS. == Introduction == Anti-ganglioside antibodies (Abs) are the most commonly recognized autoimmune markers in all forms of Guillain-Barr syndrome (GBS)[1],[2]. Association between axonal variants of GBS and specific anti-ganglioside Abs is now widely accepted[1],[3]. The full spectrum of anti-ganglioside Ab-mediated pathobiologic effects and associated mechanisms remains to be defined. Several studies suggest that GBS patients with IgG and/or IgM anti-ganglioside Abs directed against GM1 or GD1a recover more slowly and have poorer prognosis[4][14]. Anti-ganglioside Abs induce impairment of nerve repair is supported by our studies showing that monoclonal and patient-derived anti-ganglioside Abs inhibit axon regeneration and nerve repair after injury in an animal model[15],[16]. Further, we have established primary neuronal culture models in which anti-ganglioside Abs inhibit neurite/axon outgrowth[17]. Our cell culture studies establish that anti-ganglioside Abs induce inhibition via activation of small GTPase RhoA and its key downstream effector Rho kinase[17]. These models are not only critical to study the mechanisms underlying failure of axon regeneration in GBS cases with anti-ganglioside Abs and slow/poor recovery but they also provide an opportunity to examine therapeutic interventions to enhance axon regeneration in preclinical studies. Erythropoietin (EPO), 34-kD glycoprotein, is a pleiotropic cytokine originally identified for it role in erythropoiesis[18]. It also has remarkable protective activity in preclinical models of different tissue injury. Notably, EPO has been shown to be neuroprotective in animal models of stroke, spinal cord and peripheral nerve injury, and experimental autoimmune encephalomyelitis[19][21]. EPO readily penetrates the blood-brain barrier (BBB)[19]and recent phase II studies showed that peripherally administered EPO is beneficial in stroke and multiple sclerosis cIAP1 Ligand-Linker Conjugates 15 hydrochloride patients[22],[23]. Somein vitroandin vivostudies suggest that EPO may promote neurite/axon regeneration in the central as well as the peripheral nervous system[24][27]. Since a significant proportion of cases with GBS are left with residual damage despite use of current immunomodulatory therapies, i.e., intravenous immunoglobulins and plasma exchange, the need to develop therapies to protect the neural substrate and its targets during the acute phase and enhance axonal regeneration KPSH1 antibody and target reinnervation in the recovery period is increasingly realized. In view of this need, we examined the proregenerative effects of recombinant human EPO in preclinical models of inhibited axon regeneration induced with autoimmune Abs relevant to GBS. We found that EPO can significantly attenuate the anti-ganglioside Abs mediated inhibition of axon regeneration/nerve repair, and cell culture studies show that EPO induced proregenerative effect is through EPO receptor (EPOR) and sequentially activating Janus kinase 2 (JAK2)/Signal transducer and activator of transcription 5 (STAT5) pathway. == Results == == EPO enhances neurite outgrowth of normal primary sensory and motor neurons cIAP1 Ligand-Linker Conjugates 15 hydrochloride == To show proregenerative effects of EPO, we examined whether EPO enhances neurite outgrowth cIAP1 Ligand-Linker Conjugates 15 hydrochloride of primary dorsal root ganglion (DRG) and spinal motor neuron cIAP1 Ligand-Linker Conjugates 15 hydrochloride cultures. Motor and sensory neurons account for 80% and 50% of the total cell population in the primary spinal motor and DRG neuronal cultures, respectively. EPO (100 pM) significantly enhanced neurite outgrowth of.