Nerve Growth Factor and Transient Receptor Potential (TRPV1) Channel in Diabetic

Southern Illinois University Sch Of Med, Springfield IL

Investigators

Abstract

[unreadable] DESCRIPTION (provided by applicant): Diabetic peripheral neuropathy (DPN) is a common chronic complication of type 1 diabetes, characterized by progressive loss of thermal, tactile and pain sensations. The loss of peripheral sensations, coupled with impaired microvascular function in DPN can contribute to non-healing ulcers and lead to amputations. The goal of this study is to determine the mechanism(s) involved in altered thermal sensation in DPN. One hypothesis states that DPN results from altered nerve growth factor (NGF) trophic support to dorsal root ganglion (DRG) neurons. We believe that NGF regulates a thermal sensor protein, transient receptor potential channel (TRPV1), presumably by activating the NADPH oxidase superoxide generating system. Accordingly, we propose that an increase in NGF early in diabetes mediates thermal hypersensitivity, while low NGF levels or damage to sensory nerves as the disease progresses leads to sensory loss. We will test this hypothesis based on the specific aims outlined. Aim 1. To determine whether NGF regulates thermal sensation, the expression of TRPV1 and NADPH oxidase subunits in vivo. This aim will test if in vivo administration of NGF promotes hyperalgesia and whether this increases TRPV1 and NADPH oxidase subunit expression. Mice will be administered NGF by intraplantar injections, followed by analgesic testing 24 h later. DRGs and hindpaw skin obtained from vehicle and NGF treated mice will be collected to determine TRPV1 and NADPH oxidase mRNA and protein expression. Aim 2. To determine if altered thermal sensitivity in diabetes is associated with changes NGF, TRPV1 and the expression and activity of NADPH oxidase subunits. Using a double transgenic mouse model of type 1 diabetes we will measure the levels of NGF in lysates of DRGs and skin preparations, followed by measuring TRPV1 and NADPH oxidase expression using biochemical and molecular biology techniques. Preliminary studies indicate increased levels of TRPV1 in DRG neurons and hind paw skin samples correlates positively with the hyperalgesic response. Aim 3. To determine whether NGF or insulin therapy restores normal thermal sensitivity and the normal expression of TRPV1 and NADPH oxidase subunits in diabetic mice. Based on the hypothesis that a deficiency in NGF produces the hypoalgesic phenotype characteristic of type 1 diabetic mice, we will administer NGF or insulin (to maintain adequate glycemic control) to these animals and determine if it restores normal thermal sensation. The thermal thresholds of euglycemic controls and diabetic animals will be determined prior to and following administering either vehicle, NGF and insulin or a combination of these agents. The data obtained from this study would provide a better understanding of the role of NGF and the TRPV1 receptor in the controlling thermal sensations thermal in DPN. [unreadable] [unreadable] PUBLIC HEALTH RELEVANCE: The proposed project will focus on understanding some of the changes in nerve cell function, which lead to loss of pain perception in patients with diabetes, a complication termed diabetic peripheral neuropathy. We believe that the information gained by this study could contribute significantly to our appreciation of this disease and contribute to the development of novel drug therapies. [unreadable] [unreadable] [unreadable]