Abstract
Slit1 is one of the known signaling factors of the slit family and can promote neurite growth by binding to its receptor, Robo2. Upregulation of Slit1 expression in dorsal root ganglia (DRG) after peripheral nerve injury plays an important role in nerve regeneration. Each sensory neuronal soma in the DRG is encapsulated by several surrounding satellite glial cells (SGCs) to form a neural structural unit. However, the temporal and spatial patterns of Slit1 upregulation in SGCs in DRG and its molecular mechanisms are not well understood. This study examined the spatial and temporal patterns of Slit1 expression in DRG after sciatic nerve crush by immunohistochemistry and western blotting. The effect of neuronal damage signaling on the expression of Slit1 in SGCs was studied in vivo by fluorescent gold retrograde tracing and double immunofluorescence staining. The relationship between the expression of Slit1 in SGCs and neuronal somas was also observed by culturing DRG cells and double immunofluorescence labeling. The molecular mechanism of Slit1 was further explored by immunohistochemistry and western blotting after intraperitoneal injection of Bright Blue G (BBG, P2X7R inhibitor). The results showed that after peripheral nerve injury, the expression of Slit1 in the neurons and SGCs of DRG increased. The expression of Slit1 was presented with a time lag in SGCs than in neurons. The expression of Slit1 in SGCs was induced by contact with surrounding neuronal somas. Through injured cell localization, it was found that the expression of Slit1 was stronger in SGCs surrounding injured neurons than in SGCs surrounding non-injured neurons. The expression of vesicular nucleotide transporter (VNUT) in DRG neurons was increased by injury signaling. After the inhibition of P2X7R, the expression of Slit1 in SGCs was downregulated, and the expression of VNUT in DRG neurons was upregulated. These results indicate that the ATP-P2X7R pathway is involved in signal transduction from peripheral nerve injury to SGCs, leading to the upregulation of Slit1 expression.
Highlights
It is well established that peripheral nerves can be regenerated (Stoll, 1999; Vogelaar et al, 2004; Scheib and Hoke, 2013; Cattin and Lloyd, 2016; Sanna et al, 2017; Mahar and Cavalli, 2018; Tajdaran et al, 2018; Duraikannu et al, 2019)
Preliminary analyses were performed to verify the specificity of the Slit1, microtubule-associated protein 2 (MAP2), glutamine synthetase (GS), activating transcription factor 3 (ATF3) and vesicular nucleotide transporter (VNUT) and P2X7 receptor (P2X7R) antibodies used in this study (Supplementary Figure S1)
The results showed that Slit1 was expressed in the cultured sensory neuronal soma of dorsal root ganglia (DRG) but not in neurites and weakly in satellite glial cells (SGCs) (Supplementary Figures S2G–L)
Summary
It is well established that peripheral nerves can be regenerated (Stoll, 1999; Vogelaar et al, 2004; Scheib and Hoke, 2013; Cattin and Lloyd, 2016; Sanna et al, 2017; Mahar and Cavalli, 2018; Tajdaran et al, 2018; Duraikannu et al, 2019). ATP is a neurotransmitter secreted by many cell types including sensory neurons (Chaudhari, 2014), and it participates in signal transduction between neurons and SGCs (Zhang et al, 2007). ATP is an important extracellular signaling molecule that communicates through complex purine energy signaling pathways (Burnstock, 2006) This signaling pathway consists of many membrane receptors and extracellular enzymes including the P2X7 receptor (P2X7R), which belongs to the P2X family (Yegutkin, 2008). We further clarified the effect of damage signals on the expression of Slit in DRG neurons and their SGCs and clarified the role of ATP and its receptors
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