ASIC1a is required for neuronal activation via low-intensity ultrasound stimulation in mouse brain

CNS neurons have no sensory function, protected by the skull. For this reason, brain neuromodulation by ultrasound were either done at a high intensity or through auditory nerves. We demonstrate in this study CNS neurons react to ultrasound stimulation at an intensity (5 mW/cm2) far lower than typical therapeutic ultrasound (>30 mW/cm2). Using micropipette ultrasound in calcium imaging, we show ASIC1a channels play a role in the reactions of CNS neurons to ultrasound, pointing to the molecular basis for direct ultrasound neuromodulation at low intensity. Furthermore, we also show evidence of neurogenesis with the same ultrasound stimulation, suggesting potential therapeutic translation.

Inositol Polyphosphate-5-phosphatase K (Inpp5k) enhances sprouting of corticospinal tract axons after CNS trauma

ABSTRACTFailure of CNS neurons to mount a significant intrinsic growth response after trauma results in chronic functional deficits after spinal cord injury. Approaches to identify novel axon growth activators include transcriptional and repressor screening of embryonic cortical and retinal ganglion neurons in vitro. These high throughput approaches have identified several candidates; however, their inability to comprehensively model the adult CNS has resulted in their exploitation in vivo failing to stimulate significant anatomical and functional gains. To identify novel cell autonomous axon growth activators while maintaining CNS complexity, we screened intact adult corticospinal neurons (CSNs) undergoing functional plasticity after unilateral pyramidotomy. RNA-seq of intact sprouting corticospinal tract (CST) axons showed an enrichment of genes in the 3-phosphoinositide degradation pathways, including six 5-phosphatases. We explored whether Inositol Polyphosphate-5-phosphatase K (Inpp5k) could enhance CST axon growth in clinical models of CNS trauma. Overexpression of Inpp5k in intact adult CSNs enhanced sprouting of intact CST terminals into the denervated cervical cord after pyramidotomy and cortical stroke lesion. Inpp5k overexpression also stimulated sprouting of CST axons in the cervical cord after acute and chronic severe thoracic spinal contusion. We show that Inpp5k stimulates axon growth by elevating the density of active cofilin in the cytosol of labile growth cones, thus stimulating actin polymerization and enhancing microtubule protrusion into distal filopodia. This study identifies Inpp5k as a novel CST growth activator and underscores the veracity of using in vivo transcriptional screening to identify the next generation of cell autonomous factors capable of repairing the damaged CNS.SIGNIFICANCE STATEMENTNeurological recovery is limited after spinal cord injury as CNS neurons are incapable of self-repair post trauma. In vitro screening strategies exploit the intrinsically high growth capacity of embryonic CNS neurons to identify novel axon growth activators. While promising candidates have been shown to stimulate axon growth in vivo, concomitant functional recovery remains incomplete. Using transcriptional profiling of intact adult corticospinal tract neurons undergoing functional plasticity, we identified Inpp5k as a novel axon growth activator capable of stimulating CST axon growth after pyramidotomy, stroke and acute and chronic contusion injuries. These data support using in vivo screening approaches to identify novel axon growth activators.

Diversity of receptor expression in central and peripheral mouse neurons estimated from single cell RNA sequencing

Because somatosensory PNS neurons, in particular nociceptors, are specially tuned to be able to detect a wide variety of both exogenous and endogenous signals, it is widely assumed that these neurons express a greater variety of receptor genes. Because cells detect such signals via cell surface receptors, we sought to formally test the hypothesis that PNS neurons might express a broader array of cell surface receptors than CNS neurons using existing single cell RNA sequencing resources from mouse. We focused our analysis on ion channels, G-protein coupled receptors (GPCRS), receptor tyrosine kinase and cytokine family receptors. In partial support of our hypothesis, we found that mouse PNS somatosensory, sympathetic and enteric neurons and CNS neurons have similar receptor expression diversity in families of receptors examined, with the exception of GPCRs and cytokine receptors which showed greater diversity in the PNS. Surprisingly, these differences were mostly driven by enteric and sympathetic neurons, not by somatosensory neurons or nociceptors. Secondary analysis revealed many receptors that are very specifically expressed in subsets of PNS neurons, including some that are unique among neurons for nociceptors. Finally, we sought to examine specific ligand-receptor interactions between T cells and PNS and CNS neurons. Again, we noted that most interactions between these cells are shared by CNS and PNS neurons despite the fact that T cells only enter the CNS under rare circumstances. Our findings demonstrate that both PNS and CNS neurons express an astonishing array of cell surface receptors and suggest that most neurons are tuned to receive signals from other cells types, in particular immune cells.

Effects of CNS Demyelination and Myelin Recovery on Urinary Physiology

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Of note, over 80% of MS patients have urinary symptoms as one of their earliest symptoms. Since MS patients often live into older age, urinary incontinence and retention are significant problems for which few if any effective preventive or therapeutic options are available. The mechanisms by which MS contributes to urinary dysfunction are not well understood. We propose to elucidate the impact of demyelination on urinary performance using the cuprizone model, a model used to study the effects of CNS demyelination and spontaneous remyelination. We hypothesize that CNS demyelination in the cuprizone model will result in aberrant changes in urinary function, and that after remyelination occurs this dysfunction will be alleviated. C57Bl/6 mice were treated with cuprizone (0.2% w/w) for four weeks to induce demyelination. One group was allowed four additional weeks to recover from demyelination, while the other continued cuprizone treatment. Following this eight-week treatment, pressure/flow cystometry, electromyography, and molecular studies were performed to assess demyelination-induced differences in urinary performance. Cuprizone-recovery mice displayed improvements in cystometric function compared to their demyelinated littermates, as seen through improved volume sensitivity and voiding efficiency. Pharmacologic studies showed no significant changes in contractile responsiveness. Thus, we conclude that CNS demyelination results in aging-like phenotype and urinary dysfunction consistent with that observed in clinical disease. Therapeutics aimed at increasing the remyelination potential of the CNS neurons offer the possibility of alleviating urinary dysfunction associated with MS.

ASIC1a is required for neuronal activation via low-intensity ultrasound stimulation in mouse brain

ABSTRACTAccumulating evidence has shown transcranial low-intensity ultrasound can be potentially a non-invasive neural modulation tool to treat brain diseases. However, the underlying mechanism remains elusive, because the majority of studies on animal models applying rather high-intensity ultrasound that cannot be safely used in humans. Here we showed low-intensity ultrasound was able to activate neurons in the mouse brain and repeated ultrasound stimulation resulted in adult neurogenesis in specific brain regions. In vitro calcium imaging studies showed that a specific ultrasound stimulation mode, which combined with both ultrasound-induced pressure and acoustic streaming mechanotransduction, is required to activate cultured cortical neurons. ASIC1a and the tether-mode mechanotransduction were involved in the low-intensity ultrasound-mediated mechanotransduction and cultured neuron activation, which was inhibited by ASIC1a blockade and cytoskeleton-modified agents. In contrast, the inhibition of mechanical sensitive channels involved in bilayer-model mechanotransduction like Piezo or TRP proteins did not affect the ultrasound-mediated neuronal activation.SIGNIFICANCECNS neurons have no sensory function, protected by the skull. For this reason, brain neuromodulation by ultrasound were either done at a high intensity or through auditory nerves. We demonstrate in this study CNS neurons react to ultrasound stimulation at an intensity (5 mW/cm2) far lower than typical therapeutic ultrasound (>30 mW/cm2). Using micropipette ultrasound in calcium imaging, we show the reactions of CNS neurons to ultrasound is through ASIC1a channels, pointing to the molecular basis for direct ultrasound neuromodulation at low intensity. Furthermore, we also show evidence of neurogenesis with the same ultrasound stimulation, suggesting potential therapeutic translation.

Targeted disruption of dual leucine zipper kinase and leucine zipper kinase promotes neuronal survival in a model of diffuse traumatic brain injury

Background Traumatic brain injury (TBI) is a major cause of CNS neurodegeneration and has no disease-altering therapies. It is commonly associated with a specific type of biomechanical disruption of the axon called traumatic axonal injury (TAI), which often leads to axonal and sometimes perikaryal degeneration of CNS neurons. We have previously used genome-scale, arrayed RNA interference-based screens in primary mouse retinal ganglion cells (RGCs) to identify a pair of related kinases, dual leucine zipper kinase (DLK) and leucine zipper kinase (LZK) that are key mediators of cell death in response to simple axotomy. Moreover, we showed that DLK and LZK are the major upstream triggers for JUN N-terminal kinase (JNK) signaling following total axonal transection. However, the degree to which DLK/LZK are involved in TAI/TBI is unknown. Methods Here we used the impact acceleration (IA) model of diffuse TBI, which produces TAI in the visual system, and complementary genetic and pharmacologic approaches to disrupt DLK and LZK, and explored whether DLK and LZK play a role in RGC perikaryal and axonal degeneration in response to TAI. Results Our findings show that the IA model activates DLK/JNK/JUN signaling but, in contrast to axotomy, many RGCs are able to recover from the injury and terminate the activation of the pathway. Moreover, while DLK disruption is sufficient to suppress JUN phosphorylation, combined DLK and LZK inhibition is required to prevent RGC cell death. Finally, we show that the FDA-approved protein kinase inhibitor, sunitinib, which has activity against DLK and LZK, is able to produce similar increases in RGC survival. Conclusion The mitogen-activated kinase kinase kinases (MAP3Ks), DLK and LZK, participate in cell death signaling of CNS neurons in response to TBI. Moreover, sustained pharmacologic inhibition of DLK is neuroprotective, an effect creating an opportunity to potentially translate these findings to patients with TBI.