Pain-sensing sensory neurons of the dorsal root ganglion (DRG) can become sensitized (hyperexcitable) in response to pathological conditions such as diabetes. Due to insufficient knowledge concerning the mechanisms underlying this sensitization, current treatments for painful diabetic neuropathy are limited to somewhat non-specific systemic drugs, such as opioids or gabapentin, which can cause significant side effects and have high potential for abuse. Recent studies have established that T-channels make a previously unrecognized contribution to sensitization of pain responses by enhancing excitability of nociceptors. We recently showed that DRG T-currents are up-regulated in streptozotocin (STZ)-induced and ob/ob mouse models of diabetic neuropathy and contribute to enhanced pain transmission. In preliminary data, we show that the glycosylation inhibitor neuraminidase inhibits T-currents and reverses thermal and mechanical hyperalgesia in these animal models. This finding has led us to hypothesize that post-translational glycosylation of the CaV3.2 channel increases activity, enhances excitability of nociceptive DRG neurons, and consequently contributes to the symptoms of painful diabetic neuropathy.
Our specific aims are to:
Aim 1 : To use patch-clamp recordings and biophysical methods to study glycosylation-induced alterations of CaV3.2 T-channel activity in acutely dissociated DRG neurons in vitro. We propose that alterations in T-current kinetics and density can directly influence excitability of nociceptive DR cells.
Aim 2 : To investigate sites at which glycosylation of CaV3.2 T-channels occur in recombinant cells, native, and cultured DRG neurons. We propose that glycosylation of specific extracellular asparagine residues of CaV3.2 channels increases current density and membrane expression of the channel.
Aim 3 : To test the hypothesis that glycosylation of CaV3.2 T-channels in the peripheral axons of sensory neurons participates in painful PDN. We postulate that reversing glycosylation of CaV3.2 channels in diabetic animals will reverse abnormal membrane expression of these channels in somas and peripheral axons of nociceptive DRG cells, diminish cellular hyper-excitability, and reverse neuropathic pain progression in vivo. The proposed work is innovative in that a new mechanism for channel regulation will be characterized. It is medically significant because understanding the details of this regulatory pathway will facilitate development of novel drugs targeting steps in this pathway for treatment of painful neuropathies. We expect that this approach may decrease side effects from medication and reduce the potential for drug abuse in patients with painful diabetic neuropathy.
This proposed research will study the role of voltage-gated calcium channels in altered excitability of sensory neurons associated with animal models of peripheral diabetic neuropathy. This proposed study is relevant to the public health since abnormal pain sensation is unfortunately a common and difficult to treat complication of both Type 1 and Type 2 diabetes. Intractable pain has significant adverse effects on quality of life measures, and none of the available treatments can completely reverse these symptoms.
| Todorovic, S M (2016) Painful Diabetic Neuropathy: Prevention or Suppression? Int Rev Neurobiol 127:211-25 |
| Todorovic, Slobodan M (2015) Is Diabetic Nerve Pain Caused by Dysregulated Ion Channels in Sensory Neurons? Diabetes 64:3987-9 |
