George, D. S. | Search bioRxiv

bioRxiv2022

A subpopulation of peripheral sensory neurons expressing the Mas-related G Protein-Coupled Receptor d (Mrgprd) generates pain hypersensitivity in painful diabetic neuropathy.

Painful diabetic neuropathy (PDN) is one of the most common and intractable complications of diabetes. PDN is characterized by neuropathic pain accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability, axonal degeneration, and loss of cutaneous innervation. However, the complete molecular profile underlying the hyper-excitable cellular phenotype of DRG nociceptors in PDN has not been elucidated. This gap in our knowledge is a critical barrier to developing effective, mechanism-based, and disease-modifying therapeutic approaches which are urgently needed to relieve the symptoms of PDN. Using single-cell RNA sequencing we demonstrated an increased expression of the Mas-related G Protein-Coupled Receptor d (Mrgprd) in a subpopulation of DRG neurons in the well-established High-Fat Diet (HFD) mouse model of PDN. In vivo calcium imaging allowed us to demonstrate that activation of Mrgprd receptors expressed by cutaneous afferents produced DRG neuron hyper-excitability and oscillatory calcium waves. Furthermore, Mrgprd-positive cutaneous afferents persist in diabetic mice skin. Importantly, limiting Mrgprd signaling or Mrgprd-positive DRG neuron excitability, reversed mechanical allodynia in the HFD mouse model of PDN. Taken together, our data highlights a key role of Mrgprd-mediated DRG neuron excitability in the generation and maintenance of neuropathic pain in a mouse model of PDN. Hence, we propose Mrgprd as a promising accessible target for developing effective therapeutics currently unavailable for treating neuropathic pain in PDN. Furthermore, understanding which DRG neurons cell type is mediating mechanical allodynia in PDN is of fundamental importance to our basic understanding of somatosensation and may provide an important way forward for identifying cell-type-specific therapeutics to optimize neuropathic pain treatment and nerve regeneration in PDN.

neuroscience↗

bioRxiv2022

The matrisome of the murine and human dorsal root ganglion: a transcriptomal approach

The extracellular matrix (ECM) is a dynamic structure composed of a large number of molecules that can be divided into six different categories and are collectively called the matrisome. The ECM plays pivotal roles in physiological and pathological processes in many tissues, including the nervous system. Intriguingly, alterations in ECM molecules/pathways are often associated with painful human conditions and murine experimental pain models. Nevertheless, mechanistic insight into the interplay of normal or defective ECM and pain is largely lacking. To expand the knowledge on ECM composition and synthesis in the peripheral nervous system, we used a transcriptomal approach to investigate the expression and cellular origin of matrisome genes in murine and human dorsal root ganglia (DRG), containing the cell bodies of sensory neurons. Bulk RNA sequencing data showed that over 60% of all matrisome genes were expressed in both murine and human DRG, with proportionally more core matrisome genes (glycoproteins, collagens, and proteoglycans) expressed compared to matrisome-associated genes (ECM-affiliated genes, ECM regulators and secreted factors). Examination of the cellular origin of matrisome expression by single cell RNA sequencing on murine DRG revealed that core matrisome genes, especially collagens, were expressed by vascular leptomeningeal-like (fibroblast) cell types whereas matrisome-associated genes were mainly expressed by neuronal cell types. We analyzed cell-cell communication networks with the CellChat R package and predicted an important role for the Collagen signaling pathway in connecting vascular cell types and nociceptors in murine tissue, which we confirmed by analysis of spatial transcriptomic data from human DRG. RNAscope in situ hybridization and immunohistochemistry confirmed expression of collagens in fibroblasts surrounding nociceptors in human DRG. This study supports the idea that the DRG matrisome may contribute to neuronal signaling in both mouse and human. The identification of the cellular distribution of murine and human matrisome genes provides a framework to study the role of the ECM in peripheral nervous tissue and its effects on pain signaling. HighlightsO_LITranscriptomal analyses of mouse and human dorsal root ganglia (DRG) revealed that over 60% of matrisome genes are expressed by murine and human dorsal root ganglia (DRG), with over 85% of the genes with orthologues overlapping between both species. C_LIO_LIMatrisome-associated genes had the highest expression in both species and included conserved expression of annexins, S100 calcium binding proteins and cathepsins. C_LIO_LICollagens and collagen receptors are expressed by distinct cell types in murine and human DRG, suggesting that the collagen signaling pathway could be involved in cell-cell signaling. C_LI

neuroscience↗