Impaired Mitochondrial Ultrastructure in Peripheral Neurons Under Cholinergic Receptor Muscarinic 1 (CHRM1) Loss: Implications for Alzheimer's Disease and Sensory Neurodegeneration
Abstract
Cholinergic Receptor Muscarinic 1 (CHRM1) is a G protein-coupled receptor expressed in both the central and peripheral nervous systems (CNS and PNS). The degeneration of cholinergic neurons and cholinergic hypofunction are pathologies associated with Alzheimer's disease (AD). Our recent studies have demonstrated a severe loss (≥50% decrease compared to non-demented individuals) of CHRM1 protein levels in the postmortem temporal cortices, which is associated with poor survival in AD patients. Moreover, investigations utilizing an enriched cortical synaptosomal mitochondrial fraction from wild-type and Chrm1 knockout (Chrm1-/-) mice have revealed that Chrm1 loss leads to altered supramolecular assembly of oxidative phosphorylation-associated protein complexes and changes in the ultrastructure of cortical mitochondria, correlating with functional deficits in respiration. These findings directly link Chrm1 loss to an impaired mitochondrial phenotype in the CNS, emphasizing its relevance to AD pathogenesis. While the impact of CHRM1 loss in the CNS and its association with AD pathogenesis have been the focus of previous research, the significance of CHRM1 loss in peripheral neurons in AD cannot be overlooked. Reports of declining peripheral nerve conduction in AD patients prompted this study to characterize mitochondrial deficits in mouse dorsal root ganglion (DRG) neurons under Chrm1 loss conditions. Overexpression of C-terminal green fluorescent protein (GFP)-tagged Chrm1 and red fluorescence protein (MitoRFP) tagged with a mitochondrial localization signal peptide in cultured primary DRG neurons resulted in the localization of both proteins to the mitochondria, revealing the mitochondrial localization of Chrm1. Confocal time-lapse fluorescence imaging demonstrated their comigration in the neurites, suggesting potential Chrm1 localization in mitochondria. Additionally, transmission electron microscopy analysis revealed a spectrum of mitochondrial structural abnormalities, including disruption of cristae, in adult mouse DRG neurons following Chrm1 loss, thus suggesting a direct link between Chrm1 loss and mitochondrial degeneration in peripheral neurons. The observed Chrm1-GFP colocalization with mitochondria aligns with the localization of a truncated form of the homologous Chrm2 protein, which has recently been demonstrated to localize in the mitochondria. Overall, our study point to hitherto unknown localization of Chrm1 in neuronal mitochondria and implies that Chrm1 hypofunction in peripheral neurons may underlie mitochondrial malfunction, leading to sensory neurodegeneration.
Faculty Sponsors
Dr. Mohammad Golam Sabbir
Project Type
Event
Location
Alvin Sherman Library
Start Date
4-3-2024 12:30 PM
End Date
4-4-2024 1:30 PM
Impaired Mitochondrial Ultrastructure in Peripheral Neurons Under Cholinergic Receptor Muscarinic 1 (CHRM1) Loss: Implications for Alzheimer's Disease and Sensory Neurodegeneration
Alvin Sherman Library
Cholinergic Receptor Muscarinic 1 (CHRM1) is a G protein-coupled receptor expressed in both the central and peripheral nervous systems (CNS and PNS). The degeneration of cholinergic neurons and cholinergic hypofunction are pathologies associated with Alzheimer's disease (AD). Our recent studies have demonstrated a severe loss (≥50% decrease compared to non-demented individuals) of CHRM1 protein levels in the postmortem temporal cortices, which is associated with poor survival in AD patients. Moreover, investigations utilizing an enriched cortical synaptosomal mitochondrial fraction from wild-type and Chrm1 knockout (Chrm1-/-) mice have revealed that Chrm1 loss leads to altered supramolecular assembly of oxidative phosphorylation-associated protein complexes and changes in the ultrastructure of cortical mitochondria, correlating with functional deficits in respiration. These findings directly link Chrm1 loss to an impaired mitochondrial phenotype in the CNS, emphasizing its relevance to AD pathogenesis. While the impact of CHRM1 loss in the CNS and its association with AD pathogenesis have been the focus of previous research, the significance of CHRM1 loss in peripheral neurons in AD cannot be overlooked. Reports of declining peripheral nerve conduction in AD patients prompted this study to characterize mitochondrial deficits in mouse dorsal root ganglion (DRG) neurons under Chrm1 loss conditions. Overexpression of C-terminal green fluorescent protein (GFP)-tagged Chrm1 and red fluorescence protein (MitoRFP) tagged with a mitochondrial localization signal peptide in cultured primary DRG neurons resulted in the localization of both proteins to the mitochondria, revealing the mitochondrial localization of Chrm1. Confocal time-lapse fluorescence imaging demonstrated their comigration in the neurites, suggesting potential Chrm1 localization in mitochondria. Additionally, transmission electron microscopy analysis revealed a spectrum of mitochondrial structural abnormalities, including disruption of cristae, in adult mouse DRG neurons following Chrm1 loss, thus suggesting a direct link between Chrm1 loss and mitochondrial degeneration in peripheral neurons. The observed Chrm1-GFP colocalization with mitochondria aligns with the localization of a truncated form of the homologous Chrm2 protein, which has recently been demonstrated to localize in the mitochondria. Overall, our study point to hitherto unknown localization of Chrm1 in neuronal mitochondria and implies that Chrm1 hypofunction in peripheral neurons may underlie mitochondrial malfunction, leading to sensory neurodegeneration.
