1. 2013;16;E71-E83Down-Regulation of Insulin Signaling is Involved in Painful Diabetic Neuropathy in Type 2 Diabetes
   Randomized Animal Trial
   Chun-Yu Li, BS, Jun Tang, MD, Jia-Chen Hu, BS, Juan Qu, MD, Zhen-Zhen Kou, MD, PhD, Yong-Hui Liao, MD, Sheng-Xi Wu, MD, PhD, Hui Li, MD, and Yun-Qing Li, MD, PhD.

BACKGROUND: Previous theories considered that the main cause of painful diabetic neuropathy (PDN) was due to hyperglycemia. However, recent evidence indicated that hyperinsulinemia plays a greater role in type 2 diabetic metabolisms (T2DM).

OBJECTIVES: Our aim was to explore insulin signaling to determine the molecular mechanism involved in the pathogenesis of PDN in T2DM.

STUDY DESIGN: A randomized, double blind, controlled animal trial.

METHODS: We observed the localization of insulin receptor (IR) and phosphorylated insulin receptor substrate 1 (IRS-1) in the spinal cord using in situ hybridization and immunohistochemistry. Then we investigated the alternations of IR and pIRS-1 and the activity of the JAK2/STAT3 pathway by immunohistochemistry, Western Blotting, and cell culture. Finally, we detected the influence of intrathecal JAK2/STAT3 inhibitor (AG490) on nociceptive behavior and insulin signaling in ob/ob mice using Western Blotting.

RESULTS: We found that IR and pIRS-1 are mainly located in neurons in the superficial layer of the spinal dorsal horn. The expressions of IR and pIRS-1 decreased and the JAK2/STAT3 pathway activated in the spinal dorsal horn in ob/ob mice with mechanical hyperalgesia. Next, our in vitro RESULTS indicated that hyperinsulinemia and hyperglycemia impaired insulin signaling along with the activated JAK2/STAT3 pathway in differentiated human neuronal cells (SH-SY5Y). Treatment through intrathecal injection of AG490, an inhibitor of the JAK2/STAT3 pathway, alleviated mechanical hyperalgesia in ob/ob mice and prevented impaired insulin signaling in the spinal cord.

LIMITATIONS: The activation of the JAK2/STAT3 pathway could not explain the mechanism of PDN in T1DM.
 
CONCLUSIONS: We demonstrate that insulin signaling impairment in the spinal dorsal horn is associated with the activated JAK2/STAT3 pathway, which contributes to the progressive PDN in T2DM.