Single-cell transcriptomic profiling of dorsal root ganglion: an overview

Silicon Nanowire Mats Enable Advanced Bioelectrical Recordings in Primary DRG Cell Cultures

Primary dorsal root ganglion (DRG) cell cultures provide a valuable model for studying in vitro sensory transduction, neuropathies, and chronic pain, as they replicate the in vivo heterogeneity of DRG neurons and non-neuronal cells. However, traditional patch-clamp techniques are invasive and cannot capture the collective cell dynamics. While planar multielectrode arrays (MEAs) offer a non-invasive alternative, they suffer from poor cell-electrode coupling and limited resolution for identifying specific DRG neuronal types like C-fiber nociceptors, key targets in chronic pain research. This work demonstrates that silicon nanowire (SiNW) mat-based MEAs, while maintaining their reduced invasiveness, enable continuous intracellular recordings from neurons in primary rat DRG cell cultures. Supported by a cortical astrocyte feeder layer, SiNW mats promote DRG neuron and glial cell growth preserving cells' in vivo morphological and functional characteristics. Integrated into a compartmentalized MEA, they enable reliable recordings of drug-modulated neuronal activity alongside a baseline related to the astrocyte layer. The recorded signals exhibit characteristics of intracellular action potentials, suggesting spontaneous intracellular access by SiNWs. Distinct electrophysiological signatures allow identifying C-fiber nociceptors, as confirmed by patch-clamp measurements. This platform represents a powerful tool for investigating in vitro pain mechanisms, with potential applications in preclinical pain research and pharmacological translational studies.

Fucoidan reduces NET accumulation and alleviates chemotherapy-induced peripheral neuropathy via the gut-blood-DRG axis

BACKGROUND

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious adverse reaction to chemotherapy with limited treatment options. Research has indicated that neutrophil extracellular traps (NETs) are critical for the pathogenesis of CIPN. LPS/HMGB1 serve as important inducers of NETs. Here, we aimed to target the inhibition of NET formation (NETosis) to alleviate CIPN.

METHODS

Oxaliplatin (L-OHP) was used to establish a CIPN model. The mice were pretreated with fucoidan to investigate the therapeutic effect. SR-A1-/- mice were used to examine the role of scavenger receptor A1 (SR-A1) in CIPN. Bone marrow-derived macrophages (BMDMs) isolated from SR-A1-/- mice and WT mice were used to investigate the mechanism by which macrophage phagocytosis of NETs alleviates CIPN.

RESULTS

Clinically, we found that the contents of LPS, HMGB1 and NETs in the plasma of CIPN patients were significantly increased and positively correlated with the VAS score. Fucoidan decreased the LPS/HMGB1/NET contents and relieved CIPN in mice. Mechanistically, fucoidan upregulated SR-A1 expression and promoted the phagocytosis of LPS/HMGB1 by BMDMs. Fucoidan also facilitated the engulfment of NETs by BMDMs via the recognition and localization of SR-A1 and HMGB1. The therapeutic effects of fucoidan were abolished by SR-A1 knockout. RNA-seq analysis revealed that fucoidan increased sqstm1 (p62) gene expression. Fucoidan promoted the competitive binding of sqstm1 and Nrf2 to Keap1, increasing Nrf2 nuclear translocation and SR-A1 transcription. Additionally, the sequencing analysis (16 S) of microbial diversity revealed that fucoidan increased the gut microbiota diversity and abundance and increased the Bacteroides/Firmicutes ratio.

CONCLUSIONS

Altogether, fucoidan promotes the SR-A1-mediated phagocytosis of LPS/HMGB1/NETs and maintains gut microbial homeostasis, which may provide a potential therapeutic strategy for CIPN.

Anoctamin-1 is a core component of a mechanosensory anion channel complex in C. elegans

Mechanotransduction channels are widely expressed in both vertebrates and invertebrates, mediating various physiological processes such as touch, hearing and blood-pressure sensing. While previously known mechanotransduction channels in metazoans are primarily cation-selective, we identified Anoctamin-1 (ANOH-1), the C. elegans homolog of mammalian calcium-activated chloride channel ANO1/TMEM16A, as an essential component of a mechanosensory channel complex that contributes to the nose touch mechanosensation in C. elegans. Ectopic expression of either C. elegans or human Anoctamin-1 confers mechanosensitivity to touch-insensitive neurons, suggesting a cell-autonomous role of ANOH-1/ANO1 in mechanotransduction. Additionally, we demonstrated that the mechanosensory function of ANOH-1/ANO1 relies on CIB (calcium- and integrin- binding) proteins. Thus, our results reveal an evolutionarily conserved chloride channel involved in mechanosensory transduction in metazoans, highlighting the importance of anion channels in mechanosensory processes.

Interplay of Nav1.8 and Nav1.7 channels drives neuronal hyperexcitability in neuropathic pain

While voltage-gated sodium channels Nav1.7 and Nav1.8 both contribute to electrogenesis in dorsal root ganglion (DRG) neurons, details of their interactions have remained unexplored. Here, we studied the functional contribution of Nav1.8 in DRG neurons using a dynamic clamp to express Nav1.7L848H, a gain-of-function Nav1.7 mutation that causes inherited erythromelalgia (IEM), a human genetic model of neuropathic pain, and demonstrate a profound functional interaction of Nav1.8 with Nav1.7 close to the threshold for AP generation. At the voltage threshold of -21.9 mV, we observed that Nav1.8 channel open-probability exceeded Nav1.7WT channel open-probability ninefold. Using a kinetic model of Nav1.8, we showed that a reduction of Nav1.8 current by even 25-50% increases rheobase and reduces firing probability in small DRG neurons expressing Nav1.7L848H. Nav1.8 subtraction also reduces the amplitudes of subthreshold membrane potential oscillations in these cells. Our results show that within DRG neurons that express peripheral sodium channel Nav1.7, the Nav1.8 channel amplifies excitability at a broad range of membrane voltages with a predominant effect close to the AP voltage threshold, while Nav1.7 plays a major role at voltages closer to resting membrane potential. Our data show that dynamic-clamp reduction of Nav1.8 conductance by 25-50% can reverse hyperexcitability of DRG neurons expressing a gain-of-function Nav1.7 mutation that causes pain in humans and suggests, more generally, that full inhibition of Nav1.8 may not be required for relief of pain due to DRG neuron hyperexcitability.

Single-cell profiling of cellular changes in the somatic peripheral nerves following nerve injury

Injury to the peripheral nervous system disconnects targets to the central nervous system, disrupts signal transmission, and results in functional disability. Although surgical and therapeutic treatments improve nerve regeneration, it is generally hard to achieve fully functional recovery after severe peripheral nerve injury. A better understanding of pathological changes after peripheral nerve injury helps the development of promising treatments for nerve regeneration. Single-cell analyses of the peripheral nervous system under physiological and injury conditions define the diversity of cells in peripheral nerves and reveal cell-specific injury responses. Herein, we review recent findings on the single-cell transcriptome status in the dorsal root ganglia and peripheral nerves following peripheral nerve injury, identify the cell heterogeneity of peripheral nerves, and delineate changes in injured peripheral nerves, especially molecular changes in neurons, glial cells, and immune cells. Cell-cell interactions in peripheral nerves are also characterized based on ligand-receptor pairs from coordinated gene expressions. The understanding of cellular changes following peripheral nerve injury at a single-cell resolution offers a comprehensive and insightful view for the peripheral nerve repair process, provides an important basis for the exploration of the key regulators of neuronal growth and microenvironment reconstruction, and benefits the development of novel therapeutic drugs for the treatment of peripheral nerve injury.

A novel Nav1.8-FLPo driver mouse for intersectional genetics to uncover the functional significance of primary sensory neuron diversity

The recent development of single-cell and single-nucleus RNA sequencing has highlighted the extraordinary diversity of dorsal root ganglia neurons. However, the few available genetic tools limit our understanding of the functional significance of this heterogeneity. We generated a new mouse line expressing the flippase recombinase from the scn10a locus. By crossing Nav1.8Ires-FLPo mice with the AdvillinCre and RC::FL-hM3Dq mouse lines in an intersectional genetics approach, we were able to obtain somatodendritic expression of hM3Dq-mCherry selectively in the Nav1.8 lineage. The bath application of clozapine N-oxide triggered strong calcium responses selectively in mCherry+ neurons. The intraplantar injection of CNO caused robust flinching, shaking, and biting responses accompanied by strong cFos activation in the ipsilateral lumbar spinal cord. The Nav1.8Ires-FLPo mouse model will be a valuable tool for extending our understanding of the in vivo functional specialization of neuronal subsets of the Nav1.8 lineage for which inducible Cre lines are available.