Protection of renal ischemia/reperfusion injury by optogenetic stimulation of the C1 neurons
Authors: Abe Chikara , Inoue Tsuyoshi , Inglis Andrews , Viar Kenneth , Huang Li‐ping , Ye Hong , Rosin Diane , Stornetta Ruth , Okusa Mark , Guyenet Patrice 
Published: November 2023

The C1 cells, a subset of catecholaminergic neurons located in the rostral ventrolateral medulla are activated by multiple stresses (pain, hypotension, hypoxia, hypoglycemia, and infection) and contribute to the autonomic and neuroendocrine responses elicited by these stimuli. Here we investigated whether optogenetic activation of the C1 cells in conscious mice (10 min, 5 Hz) also provides protection against tissue injury. Selective expression of ChR2 by the C1 cells was obtained with unilateral stereotaxic injections of AAV2–DIO–EF1α–ChR2(H134R)–mCherry (AAV‐ChR2‐mCherry) into the left C1 region of DβHCre/0 mice. We focused on acute renal ischemia/reperfusion injury (IRI). Renal blood flow was interrupted for 26 min 24 hrs after C1 cell stimulation and renal damage was evaluated 24 hrs after the ischemia by measuring plasma creatinine level, markers of renal tissue damage (e.g. Kim‐1 mRNA) and by a quantitative histological examination of renal damage.

C1 neuron activation significantly suppressed all measured indices of IRI. Identical experiments were conducted in DβHCre/0;VGlut2flox/0 mice in which the C1 cells selectively lose their ability to release glutamate. In these mice, optogenetic activation of the C1 cells produced no protection against IRI. Next, two sets of experiments (nerve recordings and pharmacology) were done in order to determine which division of the autonomic nervous system, if any, mediates the protective effects of C1 cell stimulation. In anesthetized mice, C1 cell photostimulation increased the mass discharge of the ipsilateral cervical vagus nerve (VN) in a frequency‐dependent manner (5 – 20Hz) and increased to a lesser degree that of the contralateral VN. Renal sympathetic nerve activity also tended to increase in a stimulation frequency‐dependent manner (5 – 20Hz) but the change was not significant. C1 cell stimulation in the DβHCre/0;VGlut2flox/0 mice had not effect on the activity of the vagal or renal nerve. The protective effect of C1 neuron stimulation was abolished by administration of hexamethonium (30 mg/kg, i.p. prior to the stimulation) whereas administration of labetalol, a broad‐spectrum adrenergic receptor antagonist produced partial protection. C1 cell stimulation produced the same rise in plasma corticosterone in DβHCre/0 and DβHCre/0;VGlut2flox/0 mice (measured 1 h after stimulation).

In short, C1 cell stimulation protects against subsequent tissue injury, the protective effect requires glutamate to be released by these neurons and this protection is mediated predominantly via activation of vagal efferents with a possible contribution of sympathetic efferents but apparently without the participation of corticosterone. C1 cell stimulation likely benefits IRI by activating the cholinergic anti‐inflammatory pathway (CAP) because VN stimulation (efferent) suppresses IRI in mice via this mechanism (Inoue et al. in press).

Support or Funding Information

RO1HL028785 (PGG), R01DK085259, R01DK062324 (MDO), Japan Society for the Promotion of Science Postdoctoral Fellowships for Overseas Researchers (awarded separately to C.A. and T.I.)