Piezo2 mechanosensitive ion channel is located to sensory neurons and non-neuronal cells in rat peripheral sensory pathway: implications in pain

Piezo2 mechanotransduction channel is a crucial mediator of sensory neurons for sensing and transducing touch, vibration, and proprioception. We here characterized Piezo2 expression and cell specificity in rat peripheral sensory pathway using a validated Piezo2 antibody. Immunohistochemistry using this antibody revealed Piezo2 expression in pan primary sensory neurons (PSNs) of dorsal rood ganglia (DRG) in naïve rats, which was actively transported along afferent axons to both central presynaptic terminals innervating the spinal dorsal horn (DH) and peripheral afferent terminals in skin. Piezo2 immunoreactivity (IR) was also detected in the postsynaptic neurons of the DH and in the motor neurons of the ventral horn, but not in spinal GFAP- and Iba1-positive glia. Notably, Piezo2-IR was clearly identified in peripheral non-neuronal cells, including perineuronal glia, Schwann cells in the sciatic nerve and surrounding cutaneous afferent endings, as well as in skin epidermal Merkel cells and melanocytes. Immunoblots showed increased Piezo2 in DRG ipsilateral to plantar injection of complete Freund’s adjuvant (CFA), and immunostaining revealed increased Piezo2-IR intensity in the DH ipsilateral to CFA injection. This elevation of DH Piezo2-IR was also evident in various neuropathic pain models and monosodium iodoacetate (MIA) knee osteoarthritis (OA) pain model, compared to controls. We conclude that 1) the pan neuronal profile of Piezo2 expression suggests that Piezo2 may function extend beyond simply touch/proprioception mediated by large-sized low-threshold mechanosensitive PSNs, 2) Piezo2 may have functional roles involving sensory processing in spinal cord, Schwann cells, and skin melanocytes, and 3) aberrant Piezo2 expression may contribute pain pathogenesis.

Enhanced neuronal regeneration in the CAST/Ei mouse strain is linked to expression of differentiation markers after injury

SummaryPeripheral nerve regeneration after injury requires a broad program of transcriptional changes. We investigated the basis for the enhanced nerve regenerative capacity of the CAST/Ei mouse strain relative to C57BL/6 mice. RNA sequencing of dorsal root ganglia (DRG) showed a CAST/Ei specific upregulation of Ascl1 after injury. Ascl1 overexpression in C57BL/6 mice DRG neurons enhanced their neurite outgrowth. Ascl1 is regulated by miR-7048-3p, which is down-regulated in CAST/Ei mice. Inhibition of miR-7048-3p enhances neurite outgrowth. Following injury, CAST/Ei neurons largely retained their mature neuronal profile as determined by single cell RNAseq, whereas the C57BL/6 neurons acquired an immature profile. These findings suggest that one facet of the enhanced regenerative phenotype is preservation of neuronal identity in response to injury.

Neonatal synapse elimination in the rat submandibular ganglion: effect of retarded target growth

1. We have studied synapse elimination in the submandibular ganglion of neonatal rats to determine the effects of retarded target growth on synaptic development. Neurons of this ganglion provide parasympathetic innervation to the submandibular and sublingual salivary glands. 2. Ligating the main salivary ducts 2–4 days after birth at a point where nerve fibers were not damaged reduces gland weight by 55% during the 2nd wk after birth and 80% by adulthood. 3. In control animals, the average number of preganglionic inputs/neuron normally declines steadily during the first few weeks after birth, before stabilizing during the 5th wk at the control adult level. Between birth and adulthood, the number of ganglionic neurons increases by 150%. 4. Ganglia from duct-ligated animals showed an acceleration in the process of synapse elimination. Input number in experimental ganglia reached the control adult level during the 3rd wk after birth. This acceleration is confined solely to ganglia that innervate the underdeveloped glands. 5. The loss of inputs was not further enhanced by prolonged target atrophy. Thus average input numbers to neurons of 5th wk or adult experimental ganglia were not different from age-matched control values. 6. No differences from control values were seen in most cases for resting potentials, input resistances, or cell size. However, the increase in neuron number was retarded in experimental animals, and the number of synapses/neuronal profile was reduced in the adult animals. 7. Thus subnormal target growth leads to an acceleration in the process of synaptic elimination in neonatal rats. This acceleration may be mediated by alterations in the level of trophic factors emanating from the target.