Jigong Wang

Nociception involves complex signaling, yet intrinsic mechanisms bidirectionally regulating this process remain unexplored. Here, we show that the fibroblast growth factor 13 (FGF13)/Nav1.7 protein–protein interaction (PPI) complex bidirectionally modulates nociception, and that the FGF13/Nav1.7 ratio is upregulated in type 2 diabetic neuropathy (T2DN). PW164, an FGF13/Nav1.7 channel C-terminal tail domain (CTD) PPI interface inhibitor, which reduces complex assembly, selectively suppressed Na ⁺ currents sensitized by capsaicin-induced activation of TRPV1 channels in human induced pluripotent stem cell–derived (hIPSC-derived) sensory neurons and inhibited mechanical and thermal hyperalgesia in mice. FGF13 silencing mimics PW164 activity in culture and in vivo. Conversely, ZL192, an FGF13 ligand that stabilizes FGF13/Nav1.7 CTD assembly, sensitized Na ⁺ currents in hIPSC-derived sensory neurons and exerted pronociceptive behavioral responses in mice. ZL192’s effects were abrogated by FGF13 silencing in culture and in vivo and recapitulated by FGF13 overexpression. In a model of T2DN, PW164 injection reduced mechanical hyperalgesia locally and contralaterally without systemic side effects. In donor-derived dorsal root ganglia neurons, FGF13 and Nav1.7 proteins colocalized, and the FGF13/Nav1.7 protein ratio was upregulated in patients with T2DN. Lastly, we found that SCN9A variant V1831F, associated with painless diabetic neuropathy, abolished PW164-directed modulation of the FGF13/Nav1.7 PPI interface. Thus, FGF13 is a rheostat of nociception and promising therapeutic target for diabetic neuropathy pain.

Piezo2 expression in the normal, young adult mouse brain was examined using an anti-PIEZO2 Ab generated against a C-terminal fragment of the human PIEZO2 protein. As a positive control for Ab staining of mouse neurons, the Ab was shown to stain the majority (~90%) of mouse dorsal root ganglia (DRG) neurons, consistent with recent in situ hybridization and transcriptomic studies that also indicate Piezo2 gene expression in ~90% mouse DRG neurons. As a negative control and stringent test for specificity, the Ab failed to stain DRG satellite glial cells, which do not express Piezo2 but rather its paralog, Piezo1 . In slices of brains isolated from the same mice as the DRG, the Ab displayed high selectivity in staining only specific neuron types, including some pyramidal neurons in the neocortex and hippocampus, Purkinje cells in the cerebellar cortex, and most notably mitral cells within the olfactory bulb. Given the demonstrated role of Piezo2 channels in peripheral neurons as a low-threshold pressure sensor (i.e., ≤ 5 mm Hg) critical for gentle touch, proprioception, and the regulation of breathing and blood pressure, its expression in select brain neurons has interesting implications. In particular, we propose that the pressure sensitive channel may provide specific brain neurons with an intrinsic resonance that acts to synchronize their firing with the normal pulsatile changes in intracranial pressure (ICP) associated with breathing and cardiac cycles. This novel mechanism could serve to increase the robustness of the respiration entrained oscillations that have been recorded in both rodent and human brains across widely distributed neuronal networks. The idea of a “global rhythm” within the brain has been mainly related to the effect of nasal airflow activating mechanosensitive neurons within the olfactory epithelium, which in turn synchronize, through direct synaptic connections, mitral neurons within the olfactory bulb and then through their projections, the activity of neural networks in other brain regions, including the hippocampus and neocortex. Our proposed, non-synaptic, intrinsic resonance mechanism for tracking pulsatile ICP changes would have the advantage that spatially separated brain networks could be globally synchronized effectively at the speed of sound.

In this work, a switched-capacitor-based stimulator circuit that enables efficient energy harvesting for neurostimulation applications is presented, followed by the discussion on the optimization of the inductive coupling front-end through a codesign approach. The stimulator salvages input energy and stores it in a storage capacitor, and, when the voltage reaches a threshold, releases the energy as an output stimulus. The dynamics of the circuit are automatically enabled by a positive feedback, eliminating any stimulation control circuit blocks. The IC is fabricated in a 180 nm CMOS process and achieves a quiescent current consumption of 1.8 μA. The inductive coupling front-end is optimized as a loaded resonator, in which the input impedance of the custom rectifier directly loads the inductive loop antenna. The loaded quality factor and the rectifier's efficiency determine the reception sensitivity of the stimulator, while a balance should be achieved for the robustness of the system against dielectric medium variations by increasing the reception bandwidth. The finalized stimulator adopts a 4.9 mm × 4.9 mm inductive loop antenna and achieves an overall assembly dimension of 5 mm × 7.5 mm. Operating at the resonant frequency of 198 MHz, the stimulator works at a 14 cm distance from the transmitter in the air. An animal experiment was performed, in which a fully implanted stimulator excited the sciatic nerve of a rat that consequently triggered the movement of the limb.

Background: Central sensitization-associated synaptic plasticity in the spinal cord dorsal horn (SCDH) critically contributes to the development of chronic pain, but understanding of the underlying molecular pathways is still incomplete. Emerging evidence suggests that Wnt signaling plays a crucial role in regulation of synaptic plasticity. Little is known about the potential function of the Wnt signaling cascades in chronic pain development. Results: Fluorescent immunostaining results indicate that β-catenin, an essential protein in the canonical Wnt signaling pathway, is expressed in the superficial layers of the mouse SCDH with enrichment at synapses in lamina II. In addition, Wnt3a, a prototypic Wnt ligand that activates the canonical pathway, is also enriched in the superficial layers. Immunoblotting analysis indicates that both Wnt3a a β-catenin are up-regulated in the SCDH of various mouse pain models created by hind-paw injection of capsaicin, intrathecal (i.t.) injection of HIV-gp120 protein or spinal nerve ligation (SNL). Furthermore, Wnt5a, a prototypic Wnt ligand for non-canonical pathways, and its receptor Ror2 are also up-regulated in the SCDH of these models. Conclusion: Our results suggest that Wnt signaling pathways are regulated by nociceptive input. The activation of Wnt signaling may regulate the expression of spinal central sensitization during the development of acute and chronic pain.