Changes in the transcriptional fingerprint of satellite glial cells following peripheral nerve injury

Abstract

Satellite glial cells (SGCs) are homeostatic cells enveloping the somata of peripheral sensory and autonomic neurons. A wide variety of neuronal stressors trigger activation of SGCs, contributing to, for example, neuropathic pain through modulation of neuronal activity. However, compared to neurons and other glial cells of the nervous system, SGCs have received modest scientific attention and very little is known about SGC biology, possibly due to the experimental challenges associated with studying them in vivo and in vitro. Utilizing a recently developed method to obtain SGC RNA from dorsal root ganglia (DRG), we took a systematic approach to characterize the SGC transcriptional fingerprint by using next-generation sequencing and, for the first time, obtain an overview of the SGC injury response. Our RNA sequencing data are easily accessible in supporting information in Excel format. They reveal that SGCs are enriched in genes related to the immune system and cell-to-cell communication. Analysis of SGC transcriptional changes in a nerve injury-paradigm reveal a differential response at 3 days versus 14 days postinjury, suggesting dynamic modulation of SGC function over time. Significant downregulation of several genes linked to cholesterol synthesis was observed at both time points. In contrast, regulation of gene clusters linked to the immune system (MHC protein complex and leukocyte migration) was mainly observed after 14 days. Finally, we demonstrate that, after nerve injury, macrophages are in closer physical proximity to both small and large DRG neurons, and that previously reported injury-induced proliferation of SGCs may, in fact, be proliferating macrophages. K E Y W O R D Sdorsal root ganglion, macrophages, nerve injury, nociceptors, pain, peripheral nervous system, satellite glial cells, transcriptome

Satellite glial cells promote regenerative growth in sensory neurons

“…This analysis also indicated that the cell cycle term was enriched in macrophages, and downregulated in SGC ( Supplementary Fig. 3a, Supplementary Data 4), supporting the recent finding that macrophages but not SGC undergo cell cycle after nerve injury 38 .…”

“…1d). Whereas glutamine synthetase (Glul/GS) has been used as a SGC specific marker at the protein level 38,39 , our analysis showed a nonspecific expression in almost all cells in the DRG ( Fig. 1f and Supplementary Fig.…”

“…1e). Although prior studies suggested that SGC proliferate after injury 5,11,13 , a recent study demonstrated that cell proliferation occurred in macrophages but not in SGC seven days after injury 38 . We thus examined expression of the cell cycle markers Mki67 and Cdk1 in injury conditions and found that these cell cycle markers were mainly expressed in macrophages and blood cells/monocytes but not in SGC (Supplementary Fig.…”

“…Other SGC isolation methods rely on immunoreactivity to SK3 39 or on multiple sucrose gradients and cell plating 9 . One recent paper used immunisolation based on GS expression in SGC to examine their transicptonal profile and response to injury 38 . Whereas at the immunostaining level, GS appear specifc to SGC, it does not appear to label all SGC 38 .…”

A pharmacological interactome platform for discovery of pain mechanisms and targets

“…Sensory neurons are found within the DRG, which is composed of many different cell types, including Schwann cells and satellite glial cells. These cells are known to contribute to acute and chronic pain states (Goncalves et al, 2018;Lemes et al, 2018;Jager et al, 2020) but how they interact with sensory neurons is poorly understood. Moreover, how sensory neurons may interact with these cells through release of transmitter substances is almost completely unexplored.…”