Elevation of Tumor Necrosis Factor Alpha in Dorsal Root Ganglia and Spinal Cord is Associated with Neuroimmune Modulation of Pain in an Animal Model of Multiple Sclerosis

Abstract

Neuropathic pain (NPP) is a frequently reported symptom described by 50-80% of multiple sclerosis (MS) patients. Although Th1 cell activation is known to drive the pathology of MS, this critical step has also been suggested to be involved in the neuroimmune induction of NPP. The release of pain inducing inflammatory cytokines such as tumour necrosis factor alpha (TNFα) from activated Th1 cells may have key implications in the development of MS-induced pain. We hypothesize that immune mediated antigenic induction of inflammatory cytokines such as TNFα within dorsal root ganglia (DRG) and spinal cord (SC) facilitate the cellular events underlying induction of pain. A rat experimental autoimmune encephalomyelitis (EAE) model of MS was utilized to identify the cellular source and expression changes of TNFα protein and mRNA in the DRG and SC. The TNFα levels in the DRG and SC were correlated with the behavioral testing indicative of NPP. We show significant increases in TNFα protein and mRNA expression in DRG and SC of EAE animals at 12 days post induction (EAE12) relative to naïve control (NC) and active control (AC) groups. Further, we show increased TNFα protein and mRNA expression at the dorsal root entry point, which suggests the anterograde transport of both protein and mRNA. Further, the onset of NPP coincides with increased TNFα expression in the SC. These results demonstrate that the elevated expression of TNFα in the DRG and SC may be associated with the pathological induction of NPP in an animal model of MS.

Experimental Autoimmune Encephalomyelitis (EAE)-Induced Elevated Expression of the E1 Isoform of Methyl CpG Binding Protein 2 (MeCP2E1): Implications in Multiple Sclerosis (MS)-Induced Neurological Disability and Associated Myelin Damage

“…Thus, MeCP2 represents a key biological target molecule where epigenetic interventional strategies aimed at both DNA methylation and histone modifications could be optimized to generate a novel therapeutic drug to halt myelin damage associated with MS [78]. Therefore, studying the link between MeCP2 and BDNF and other downstream biological targets such as NGF [5,10], TNFα [6], and CX3CL1 [9] in MS may lead to new epigenetic therapeutic approaches to promote re-myelination and myelin repair in MS. …”

“…A total of n = 4 mice were used per time point per group. As per our standard in house protocols [6,7,9,11], EAE mice were immunized subcutaneously (SQ) with 200 µg MOGp35–55 in 200 µL of Complete Freund’s adjuvant (CFA) at the lower/upper back at Day 0 (induction kits from Hooke Laboratories (Lawrence, MA 01843, USA) (Cat, EK-2110)). Animals received two intraperitoneal (IP) injections of pertussis toxin (PTX: List Biological Laboratories; #179B) (0.2 µg in 100 µL of PBS at Days 0 and 1) to open up the blood brain barrier and facilitate the entry of pathogenic T cells to the CNS.…”

“…Freshly harvested DRG and SC tissue were placed in RNA later stabilization solution (Ambion Cat#AM7020, Burlington, ON, Canada) until being processed. Whole DNA/RNA and protein was purified using commercially available kits (AllPrep DNA/RNA/protein, Qiagen, Toronto, ON, Canada) as described in our previous publications [6,8,51]. …”

“…Using an animal model of MS, we have published several publications that identify the importance of the anatomical connection between the dorsal root ganglia (DRG) and spinal cord (SC) [5,6,7] in regard to myelin repair. In addition, several of our publications have identified a common interactive signaling network among cytokines, chemokines and neurotrophins that regulate the myelin repair process [6,7,8,9].…”

“…In addition, several of our publications have identified a common interactive signaling network among cytokines, chemokines and neurotrophins that regulate the myelin repair process [6,7,8,9]. We have identified several key biological targets in this pathway [5,7,8,9,10,11], However, we have now expanded this list of biological targets to include the upstream transcriptional repressor of BDNF known as methyl CpG binding protein 2 (MeCP2) [11,12,13].…”