Transcriptomic and histological characterization of telocytes in the human dorsal root ganglion

Abstract

Telocytes are interstitial cells with long processes that cover distances in tissues and likely coordinate interacts with other cell types. Though present in central and peripheral neuronal tissues, their role remains unclear. Dorsal root ganglia (DRG) house pseudounipolar afferent neurons responsible for signals such as temperature, proprioception and nociception. This study aimed to investigate the presence and function of telocytes in human DRG by investigating their transcriptional profile, location and ultrastructure. Sequencing data revealed CD34 and PDGFRA expressing cells comprise roughly 1.5-3% of DRG cells. Combined expression of CD34 and PDGFRA is a putative marker gene set for telocytes. Further analysis identified nine subclusters with enriched cluster-specific genes. KEGG and GO pathway analysis suggested vascular, immune and connective tissue associated putative telocyte subtypes. Over 3000 potential receptor-ligand interactions between sensory neurons and these CD34 and PDGFRA expressing putative telocytes were identified using a ligand-receptors interactome platform. Immunohisto-chemistry showed CD34+ telocytes in the endoneural space of DRGs, next to neuron-satellite complexes, in perivascular spaces and in the endoneural space between nerve fibre bundles, consistent with pathway analysis. Transmission electron microscopy (TEM) confirmed their location identifying characteristic elongated nucleus, long and thin telopods containing vesicles, surrounded by a basal lamina. This is the first study that provides gene expression analysis of telocytes in complex human tissue such as the DRG, highlighting functional differences based on tissue location with no significant ultrastructural variation.

Keywords: dorsal root ganglion; human; telocyte.

Figure 1:

Identification of Telocytes in Human DRG Using Single-Cell Transcriptomics. (A-B) UMAP plots showing the expression of gene markers used to identify telocytes. (C) UMAP plots showing the expression of gene markers that reveal multiple telocyte clusters in the human DRG.

Figure 2:

Interactome Analysis Between Neurons and Telocytes in Human DRG. (A) Sankey plot showing the top 50 unique telocyte-to-hDRG ligand-receptor interactions. B) Sankey plot illustrating the top 50 hDRG-to-telocyte ligand-receptor interactions.

Figure 3:

Single and multiple labelling immunohistochemistry human DRG. (A) Immuno-reactivity for CD34 is present in vascular endothelium (long arrow) and in telocytes (short arrows) next to neuronal cell bodies. Nuclei are stained with DAPI. Cell bodies contained autofluorescent lipofuscin (star). Bar = 50 mm. (B) Double labelling with the marker of satellite cells, S100 (pale blue) shows the presence of telocytes and their telopods (red) outside of the neuron-satellite complex. Nuclei are stained with DAPI. Bar = 100 μm. (C) Confocal laser scanning image with a thickness of 1 μm shows the presence of CD34+ fibres (short arrows) next to neuron-satellite complexes, in the endoneural space and next to blood vessels (long arrows). Nuclei are stained with DAPI. Bar = 75 μm.

Figure 4:

(A) Toluidin blue stained semithin section with neuron-satellie complexes, nerve fibres, capillaries (stars) and pale surrounding perivascular space. Telocyte nuclei in the perivascular and endoneural space are indicated with arrows. Bar = 30 μm. (B) Transmission electron microscope image of a human DRG. Telocyte (TC) with telopods (arrows) between the perivascular space of a capillary (EC – endothelial cell nucleus) and the complex of nerve cell (neuronal soma) and satellite glia cell (SGC). Bar = 4 μm.

Figure 5:

(A) The electron microscopical image shows the elongated nucleus of telocytes, arrow indicate the basal lamina usually associated with soma and telopods of telocytes. Bar = 2 μm. (B) Electron microscopical image of a telocyte with cell-cell contacts indicated with arrows. Bar = 2 μm.