Role of a diabetes-specific circular RNA in diabetic neuropathic pain

About This Grant

Project Summary Diabetic neuropathic pain (DNP) is a major public problem. Current successful treatment for this disorder are highly limited because most medications used are ineffective and non-specific. Changes of gene expression in primary sensory neurons of the dorsal root ganglion (DRG) are believed to be the underlying molecular basis for the pathogenesis of DNP. Understanding the expression and function of DNP- specific gene in the DRG may provide highly precise and effective therapy for this disorder. We recently identified a DNP-specific circular RNA that is 100% identical between mouse and human and upregulated only in the DRG neurons from the mice with type 1 diabetes mellitus (T1DM) and from the mice and human donors with type 2 diabetes mellitus (T2DM). Because it is formed by back splicing from exon 4 to exon 2 of the Rps6kb1 pre-RNA, we named it cRps6kb1 (cRps). cRps upregulation may be due to an increase in the expression of heterogeneous nuclear ribonucleoprotein L (HNRNPL, an RNA-binding protein/alternative splicing factor) in the diabetic DRGs. Blocking this upregulation alleviated nociceptive hypersensitivity in diabetic mice, likely through a loss of competitive binding of cRps to PUM2 (Pumilio RNA-binding family member 2, a translational repressor) and corresponding increase in PUM2 interaction with the 3'-untranslated region of C-C chemokine ligand 2 mRNA (Ccl2 3'-UTR), leading to translational inhibition and degradation of Ccl2 mRNA in the diabetic DRGs. Giving that CCL2 is a driver in the genesis of neuropathic pain, DRG upregulated cRps is responsible for DNP likely through CCL2 increase in the DRG. This proposal will further examine whether and how DRG cRps contributes to DNP. In Specific Aim 1, we will determine whether blocking cRps upregulation in the DRGs alleviates established nociceptive hypersensitivity under the conditions of streptozotocin (STZ)-induced T1DM and diet-induced obesity T2DM. We will also investigate whether mimicking DRG cRps upregulation produces DNP-like symptoms in naive mice. In Specific Aim 2, we will investigate whether cRps and HNRNPL are time-dependently upregulated and whether DRG cRps upregulation results from an increase of HNRNPL expression in the DRG neurons from mice or human donors under the DNP conditions of T1DM or T2DM. In Specific Aim 3, we will first examine whether the expression of CCL2 and its receptor CCR2 is time-dependently increased in the diabetic DRGs and if CCL2 increase is required for nociceptive hypersensitivity under the conditions of STZ-induced T1DM or diet-induced obesity T2DM. We will then examine whether cRps upregulation contributes to CCL2 increase in diabetic DRG neurons. Finally, we will explore whether cRps upregulation increases its competitive binding to PUM2, leading to a consequent release of Ccl2 3'-UTR from PUM2 binding and the promotion of translational activity and stability of Ccl2 mRNA in diabetic DRG neurons. Completing this proposal will not only identify a previously unknown mechanism underlying DNP but may also provide promising treatment of this disorder.