Cholinergic Regulation of hnRNPA2/B1 Translation by M1 Muscarinic Receptors

Abstract

Cholinergic vulnerability, characterized by loss of acetylcholine (ACh), is one of the hallmarks of Alzheimer's disease (AD). Previous work has suggested that decreased ACh activity in AD may contribute to pathological changes through global alterations in alternative splicing. This occurs, at least partially, via the regulation of the expression of a critical protein family in RNA processing, heterogeneous nuclear ribonucleoprotein (hnRNP) A/B proteins. These proteins regulate several steps of RNA metabolism, including alternative splicing, RNA trafficking, miRNA export, and gene expression, providing multilevel surveillance in RNA functions. To investigate the mechanism by which cholinergic tone regulates hnRNPA2/B1 expression, we used a combination of genetic mouse models and in vivo and in vitro techniques. Decreasing cholinergic tone reduced levels of hnRNPA2/B1, whereas increasing cholinergic signaling in vivo increased expression of hnRNPA2/B1. This effect was not due to decreased hnRNPA2/B1 mRNA expression, increased aggregation, or degradation of the protein, but rather to decreased mRNA translation by nonsense-mediated decay regulation of translation. Cell culture and knockout mice experiments demonstrated that M1 muscarinic signaling is critical for cholinergic control of hnRNPA2/B1 protein levels. Our experiments suggest an intricate regulation of hnRNPA2/B1 levels by cholinergic activity that interferes with alternative splicing in targeted neurons mimicking deficits found in AD.

Vesicular acetylcholine transporter (VAChT) over‐expression induces major modifications of striatal cholinergic interneuron morphology and function

“…Alternatively, increased VAChT expression may have long‐term effects in gene expression as we previously observed (Kolisnyk et al . ). This may also contribute to the profound morphological changes we detected in these cholinergic interneurons as discussed below.…”

“…For example, ChAT–ChR2 mice have increased levels of hnRNPA2/B1, an essential splicing regulator (Kolisnyk et al . ). However, although these abnormalities in gene expression in targeted tissues and behavioral functions are now documented, whether VAChT over‐expression can have long‐term consequences for cholinergic neuron function is unknown.…”

Selective decrease of cholinergic signaling from pedunculopontine and laterodorsal tegmental nuclei has little impact on cognition but markedly increases susceptibility to stress

“…Also, it is possible that increased latency to respond observed in the PVD-R may reflect a decrease in motivation. Further studies using more sensitive methods to investigate dopamine release, such as microdialysis in freely moving mice (39), in vivo voltammetry (17), or in vivo dopaminergic fluorescence sensors (103,104), as well as behavioral tasks interrogating motivation would be necessary to determine the influence of dopamine in these VAChTmutant mice.…”

“…Changes in VAChT expression and function have a direct influence on the amount of ACh released from nerve terminals (17,18,(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38). Notably, decreased VAChT expression affects cholinergic signaling (17,18,20,23,25,26,30,31,36,37,(38)(39)(40)(41)(42)(43)(44)(45)(46)(47), suggesting that VAChT is the unique transporter for ACh. Importantly, VAChT deletion disturbs ACh storage and release but does not kill cholinergic neurons (25,26,38).…”

Shortened TDP43 isoforms upregulated by neuronal hyperactivity drive TDP43 pathology in ALS

“…In contrast to what we observed with N-terminal TDP43, there was no reciprocal activity-dependent change in C-terminal TDP43 abundance or localization by immunocytochemistry, and we failed to observe any differences in C-terminally labeled TDP43-D2 upon addition of TEA or TTX, arguing against a cleavage event. However, previous studies demonstrated that neuronal activity regulates the abundance of similar RNA-binding proteins through alternative splicing (57,58). We therefore considered the possibility that activity gives rise to distinct TDP43 isoforms through alternative splicing.…”