Role of spinal MCP-1-ERK-KIF17/NR2B signaling pathway in maintenance of type 2 diabetic neuropathic pain in rats

Abstract

Objective To explore the role of spinal monocyte chemoattractant protein-1 (MCP-1) -extracellular signal-regulated protein kinase (ERK) -kinesin superfamily motor protein 17 (KIF17) /N-methyl-D-aspartate receptor subunit 2B (NR2B) signaling pathway in the maintenance of type 2 diabetic neuropathic pain (DNP) in rats. Methods Type 2 diabetes mellitus was induced by a high-fat and high-sucrose diet and intraperitoneal streptozotocin (STZ) 35 mg/kg, and confirmed by fasting blood glucose level≥16.7 mmol/L 3 days later in male Sprague-Dawley rats aged 6 weeks.Type 2 DNP was confirmed when the mechanical paw withdrawal threshold (MWT) and thermal paw withdrawl latency (TWL) measured on day 14 after STZ administration decreased to < 80% of the baseline value.The rats with type 2 DNP were randomly divided into 4 groups (n=36 each) using a random number table: type 2 DNP group (group DNP) , type 2 DNP + MCP-1 neutralizing antibody group (group DM) , type 2 DNP + ERK inhibitor group (group DE) and type 2 DNP + dimethyl sulfoxide group (group DD) . In DM, DE and DD groups, 0.1 ng/μl MCP-1 neutralizing antibody 10 μl, 0.5 μg/μl U0126 10 μl and 5 % dimethyl sulfoxide 10 μl were injected intrathecally, respectively, once a day for 14 consecutive days starting from 14 days after administration of STZ.Another 36 normal rats fed a common forage diet were adopted as control group (group C) . MWT and TWL were measured before STZ injection and at 1, 3, 7 and 14 days after STZ injection (T0-4) . Nine rats were sacrificed after measurement of pain thresholds at T1-4, and the lumbar segments (L4-6) of the spinal cord were removed for determination of the expression of phosphorylated ERK (p-ERK) , KIF17 and phosphorylated NR2B (p-NR2B) by Western blot. Results Compared with group C, the MWT was significantly decreased, the TWL was shortened, and the expression of p-ERK, KIF17 and p-NR2B was up-regulated at T1-4 in DNP, DM, DE and DD groups.Compared with group DNP, the MWT at T3-4 in group DM and at T2-4 in group DE was significantly increased, the TWL at T3-4 in group DM and at T2-4 in group DE was prolonged, and the expression of p-ERK, KIF17 and p-NR2B was down-regulated at T2-4 in DM and DE groups, and no significant changes were found in the parameters mentioned above in group DD. Conclusion Spinal MCP-1-ERK-KIF17/NR2B signaling pathway is involved in the maintenance of type 2 DNP in rats. Key words: Diabetes mellitus, type 2; Neuropathic pain; Chemokine CCL2; Extracellular Signal-Regulated MAP Kinases; Receptors, N-Methyl-D-Aspartate; Kinesin; Spinal cord