REGULATION OF FUNCTIONAL EXPRESSION OF MECHANOSENSITIVE TRPV4 CHANNEL IN THE DISTAL NEPHRON BY DIETARY POTASSIUM AND SODIUM INTAKE

The Ca2+-permeable TRPV4 channel is predominantly expressed in the distal nephron (DN) and its activity is essential for [Ca2+]i elevations in response to increased tubular flow. Here, I probed the physiological mechanisms controlling TRPV4 function and expression in the DN. I found that renal TRPV4 expression and mRNA levels were significantly increased by high K+ diet (5%) and decreased by dietary K+ restriction (0.003%). In contrast, variations in Na+ regimen had no apparent effect on TRPV4 expression and mRNA levels. Regulation of TRPV4 protein expression by K+ diet was independent of aldosterone action, since saturation of systemic mineralocorticoid signaling with DOCA, a precursor of aldosterone, had little effect on TRPV4 protein abundance in the kidney. Confocal immunofluorescence in split-opened DNs showed that high K+ and Na+ intake resulted in redistribution of the channel towards the apical plasma membrane of DN cells, while K+ and Na+ restrictions caused cytosolic distribution of TRPV4. Augmented TRPV4 expression and localization to the apical plasma membrane during high K+ and Na+ intake were associated with significantly augmented flow-induced [Ca2+]i responses in DN cells. In summary, my findings demonstrate that high K+ and Na+ intake regulate TRPV4 status to properly respond to elevated tubular flow during these physiological stimuli. I also propose that impaired regulation of TRPV4 in the DN during variations in dietary intake may result in systemic defects in K+ and Na+ balance contributing to cardiovascular abnormalities

Chronic Restraint Stress Impairs Voluntary Wheel Running but Has No Effect on Food-Motivated Behavior in Mice

Chronic restraint stress is known to cause significant alterations of mitochondrial biology. However, its effects on effort-based behavior and the sensitivity of these effects to treatments that restore mitochondrial function have not been assessed. Based on the hypothesis that the behavioral consequences of this stressor should be more severe for an energy demanding activity than for an energy procuring activity, we compared the effects of chronic restraint stress on the performance of male mice trained to use a running wheel or to nose poke for a food reward in an operant conditioning cage. In accordance with our hypothesis, we observed that exposure of mice to 2-hour daily restraint sessions for 14 to 16 days during the light phase of the cycle reliably decreased voluntary wheel running but had no effect on working for food in a fixed ratio 10 schedule of food reinforcement or in a progressive ratio schedule of food reinforcement. This dissociation between the two types of behavioral activities could reflect an adaptive response to the constraint imposed by chronic restraint stress on mitochondria function and its negative consequences on energy metabolism. To determine whether it is the case, we administered mesenchymal stem cells intranasally to chronically restrained mice to repair the putative mitochondrial dysfunction induced by chronic restraint stress. This intervention had no effect on wheel running deficits. Assessment of mitochondrial gene expression in the brain of mice submitted to chronic restraint stress revealed an increase in the expression of genes involved in mitochondrial biology that showed habituation with repetition of daily sessions of restraint stress. These original findings can be interpreted to indicate that chronic restraint stress induces behavioral and mitochondrial adjustments that contribute to metabolic adaptation to this stressor and maintain metabolic flexibility

Resolution of Cisplatin-Induced Fatigue Does Not Require Endogenous Interleukin-10 in Male MiceB

Based on previous results showing a pivotal role of endogenous interleukin-10 (IL-10) in the recovery from cisplatin-induced peripheral neuropathy, the present experiments were carried out to determine whether this cytokine plays any role in the recovery from cisplatin-induced fatigue in male mice. Fatigue was measured by decreased voluntary wheel running in mice trained to run in a wheel in response to cisplatin. Mice were treated with a monoclonal neutralizing antibody (IL-10na) administered intranasally during the recovery period to neutralize endogenous IL-10. In the first experiment, mice were treated with cisplatin (2.83 mg/kg/day) for five days and IL-10na (12 μg/day for three days) five days later. In the second experiment, they were treated with cisplatin (2.3 mg/kg/day for 5 days twice at a five-day interval) and IL10na (12 μg/day for three days) immediately after the last injection of cisplatin. In both experiments, cisplatin decreased body weight and reduced voluntary wheel running. However, IL-10na did not impair recovery from these effects. These results show that the recovery from the cisplatin-induced decrease in wheel running does not require endogenous IL-10 in contrast to the recovery from cisplatin-induced peripheral neuropathy

Nasal Mesenchymal Stem Cell Treatment for the Repair of Chemotherapy-Induced Neurotoxicities: Let the Trojan Horse In!

In this thesis, we show for the first time that nasal administration of mesenchymal stem cells (MSC) promotes recovery from chemotherapy-induced cognitive impairment and chemotherapy-induced peripheral neuropathy (CIPN), two major side effects of cancer treatment that frequently persist long into survivorship. We demonstrate that nasal administration of MSC reverses cognitive impairments induced by cisplatin treatment in mice. Resting state functional magnetic resonance imaging study of network connectivity in the brain shows that cisplatin treatment leads to a decrease in global neuronal connectivity. Connectome analysis reveals a decrease in path length in cisplatin-treated mice, which is reversed by MSC treatment. Functionally, nasally administered MSC reversed cisplatin-induced synaptosomal mitochondrial dysfunction and abnormal mitochondrial morphology. Moreover, MSC reversed cisplatin-induced morphological changes of cortical white matter structures. RNA sequencing analysis revealed mitochondrial oxidative phosphorylation as a top pathway activated by MSC administration to cisplatin-treated mice, supporting the concept that MSC may act by resolving neuronal mitochondrial dysfunction leading to restoration of the cognitive deficits and associated brain damage after chemotherapy. We show that cisplatin treatment leads to mitochondrial dysfunction and death of neural stem cells (NSC) in vitro as well as a decrease in the number of Doublecortin (DCX)+ neural progenitor cells in the brain neurogenic niches. Nasal MSC treatment rescues damaged NSC from cell death in vitro and reverses the loss of DCX+ cells in vivo. Furthermore, we show that MSC donate mitochondria to NSC damaged by cisplatin in vitro, contributing to the beneficial effects of MSC in rescuing damaged NSC. Mitochondrial transfer is potentiated by overexpression of the Rho-GTPase Miro1. Moreover, mitochondrial transfer from MSC to NSC is associated with restoration of mitochondrial membrane potential and protection against cisplatin-induced cell death. Interestingly, we also demonstrate that nasal MSC administration resolves symptoms of CIPN, including mechanical allodynia and spontaneous pain. Nasal MSC treatment normalizes cisplatin-induced mitochondrial dysfunction in DRG neurons as well as tibial nerves and reverses the retraction of peripheral nerves endings in the paw of cisplatin-treated mice. As a mechanism of MSC action, we show that IL-10 production by nasally administered MSC is critical for reversal of CIPN. In addition, IL-10 signaling via IL-10 receptors expressed by peripheral sensory neurons is crucial for MSC-mediated recovery of CIPN symptoms. We report that nasally administered MSC can be traced in the brain, meninges of the brain and spinal cord meninges. We observed an abundant presence of MSC within 30 min-1 hour after administration in the meninges of the brain, where MSC were still detected up to 7 days later. MSC were also present in the brain and meninges of the spinal cord at 12-24 hours albeit in low numbers. Interestingly, mitochondria derived from MSC were taken up by macrophages in the meninges of the brain which induced macrophages to increase production of IL-10. The latter suggest that the meningeal compartment may ‘educate’ immune cells to a regenerative healing phenotype. Finally, we review the mechanisms and functions of mitochondrial transfer from MSC to damaged neural cells

Nasal administration of mesenchymal stem cells reverses chemotherapy-induced peripheral neuropathy in mice

Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most frequently reported adverse effects of cancer treatment. CIPN often persists long after treatment completion and has detrimental effects on patient's quality of life. There are no efficacious FDA-approved drugs for CIPN. We recently demonstrated that nasal administration of mesenchymal stem cells (MSC) reverses the cognitive deficits induced by cisplatin in mice. Here we show that nasal administration of MSC after cisplatin- or paclitaxel treatment- completely reverses signs of established CIPN, including mechanical allodynia, spontaneous pain, and loss of intraepidermal nerve fibers (IENF) in the paw. The resolution of CIPN is associated with normalization of the cisplatin-induced decrease in mitochondrial bioenergetics in DRG neurons. Nasally administered MSC enter rapidly the meninges of the brain, spinal cord and peripheral lymph nodes to promote IL-10 production by macrophages. MSC-mediated resolution of mechanical allodynia, recovery of IENFs and restoration of DRG mitochondrial function critically depends on IL-10 production. MSC from IL-10 knockout animals are not capable of reversing the symptoms of CIPN. Moreover, WT MSC do not reverse CIPN in mice lacking IL-10 receptors on peripheral sensory neurons. In conclusion, only two nasal administrations of MSC fully reverse CIPN and the associated mitochondrial abnormalities via an IL-10 dependent pathway. Since MSC are already applied clinically, we propose that nasal MSC treatment could become a powerful treatment for the large group of patients suffering from neurotoxicities of cancer treatment

B cells drive neuropathic pain–related behaviors in mice through IgG–Fc gamma receptor signaling

Neuroimmune interactions are essential for the development of neuropathic pain, yet the contributions of distinct immune cell populations have not been fully unraveled. Here, we demonstrate the critical role of B cells in promoting mechanical hypersensitivity (allodynia) after peripheral nerve injury in male and female mice. Depletion of B cells with a single injection of anti-CD20 monoclonal antibody at the time of injury prevented the development of allodynia. B cell–deficient (muMT) mice were similarly spared from allodynia. Nerve injury was associated with increased immunoglobulin G (IgG) accumulation in ipsilateral lumbar dorsal root ganglia (DRGs) and dorsal spinal cords. IgG was colocalized with sensory neurons and macrophages in DRGs and microglia in spinal cords. IgG also accumulated in DRG samples from human donors with chronic pain, colocalizing with a marker for macrophages and satellite glia. RNA sequencing revealed a B cell population in naive mouse and human DRGs. A B cell transcriptional signature was enriched in DRGs from human donors with neuropathic pain. Passive transfer of IgG from injured mice induced allodynia in injured muMT recipient mice. The pronociceptive effects of IgG are likely mediated through immune complexes interacting with Fc gamma receptors (FcγRs) expressed by sensory neurons, microglia, and macrophages, given that both mechanical allodynia and hyperexcitability of dissociated DRG neurons were abolished in nerve-injured FcγR-deficient mice. Consistently, the pronociceptive effects of IgG passive transfer were lost in FcγR-deficient mice. These data reveal that a B cell–IgG–FcγR axis is required for the development of neuropathic pain in mice