Mobley, W. C. | Search bioRxiv

bioRxiv2022

BDNF and TRiC-inspired Reagents Rescue Cortical Synaptic Deficits in a Mouse Model of Huntington's Disease

Huntingtons disease (HD) results from a CAG repeat expansion in the gene for Huntington (HTT) resulting in expansion of the polyglutamine (Q) tract in the mutant protein (mHTT). Synaptic changes are early manifestations of neuronal dysfunction in HD. However, the mechanism(s) by which mHTT impacts synapse formation and function is not well defined. Herein we explored HD pathogenesis in the BACHD and the {Delta}N17-BACHD mouse models of HD by examining cortical synapse formation and function in primary cultures maintained for up to 35 days (DIV35). We identified synapses by immunostaining with antibodies against pre-synaptic (Synapsin 1) and a post-synaptic (PSD95) marker. Consistent with earlier studies, cortical neurons from both WT and the HD models began to form synapses at DIV14; at this age there were no genotypic differences in synapse numbers. However, from DIV21 through DIV35 BACHD neurons showed progressively smaller numbers of synapses relative to WT neurons. Remarkably, BACHD synaptic deficits were completely rescued by treating cultures with BDNF. Building on earlier studies using reagents inspired by the chaperonin TRiC, we found that addition of the recombinant apical domain of CCT1 partially rescued synapse number. Unexpectedly, unlike BACHD cultures, synapses in {Delta}N17-BACHD cultures showed a progressive increase in number as compared to WT neurons, thus distinguishing synaptic changes in these HD models. Using multielectrode arrays, we discovered age-related functional deficits in BACHD cortical cultures with significant differences present by DIV28. As for synapse number, BDNF treatment prevented most synaptic deficits, including mean firing rate, spikes per burst, inter-burst interval, and synchrony. The apical domain of CCT1 showed similar, albeit less potent effects. These data are evidence that deficits in HD synapse number and function can be replicated in vitro and that treatment with either BDNF or a TRiC-inspired reagent can prevent them. Our findings support the use of cellular models to further explicate HD pathogenesis and its treatments.

neuroscience↗

bioRxiv2018

Swedish Nerve Growth Factor Mutation (NGFR100W) Defines a Role for TrkA and p75NTR in Nociception

Nerve growth factor (NGF) exerts multiple functions on target neurons throughout development. The recent discovery of a point mutation leading to a change from arginine to tryptophan at residue 100 in the mature NGF{beta} sequence (NGFR100W) in patients with hereditary sensory and autonomic neuropathy, type V (HSAN V), made it possible to distinguish the signaling mechanisms that lead to two functionally different outcomes of NGF: trophic versus nociceptive. We performed extensive biochemical, cellular and live imaging experiments to examine the binding and signaling properties of NGFR100W. Our results show that, similar to the wildtype NGF (wtNGF), the naturally occurring NGFR100W mutant was capable of binding to and activating the TrkA receptor and its downstream signaling pathways to support neuronal survival and differentiation. However, NGFR100W failed to bind and stimulate the 75kD neurotrophic factor receptor (p75NTR)-mediated signaling cascades (i.e. the RhoA-Cofilin pathway). Intraplantar injection of NGFR100W into adult rats induced neither TrkA-mediated thermal nor mechanical acute hyperalgesia, but retained the ability to induce chronic hyperalgesia based on agonism for TrkA signaling. Taken together, our studies provide evidence that NGFR100W retains trophic support capability through TrkA and one aspect of its nociceptive signaling, but fails to engage p75NTR signaling pathways. Our findings suggest that wtNGF acts through TrkA to regulate the delayed priming of nociceptive responses. The integration of both TrkA and p75NTR signaling thus appears to regulate neuroplastic effects of NGF in peripheral nociception.\n\nSignificance StatementIn the present study, we characterized the naturally occurring NGFR100W mutant that is associated with hereditary sensory and autonomic neuropathy, type V. We have demonstrated for the first time that NGFR100W retains trophic support capability through TrkA but fails to engage p75NTR signaling pathways. Furthermore, following Intraplantar injection into adult rats, NGFR100W induced neither thermal nor mechanical acute hyperalgesia, but retained the ability to induce chronic hyperalgesia. We have also provided evidence that the integration of both TrkA-and p75NTR-mediated signaling thus appears to regulate neuroplastic effects of NGF in peripheral nociception. Our study with NGFR100W suggests that it is possible to uncouple trophic effect from nociceptive function, both induced by wildtype NGF.\n\nAbbreviations

neuroscience↗