Biology subjects

Caldwell, G. A.

Publications and source records attributed to Caldwell, G. A..

3 recordsLinked to original sources

bioRxiv2020

Conserved nicotine-activated neuroprotective pathways involve mitochondrial stress

Tobacco smoking is a risk factor for several human diseases. Conversely, smoking also reduces the prevalence of Parkinsons disease (PD), whose hallmark is degeneration of substantia nigra dopaminergic neurons (DNs). We use C. elegans as a model to investigate whether tobacco-derived nicotine activates nicotinic acetylcholine receptors (nAChRs) to selectively protect DNs. Using this model we demonstrate conserved functions of DN-expressed nAChRs. We find that DOP-2, a D3-receptor homolog, MCU-1, a mitochondrial calcium uniporter, and PINK-1, PTEN-induced kinase 1, are required for nicotine-mediated protection of DNs. Together, our results support involvement of calcium-dependent mitochondrial stress activation of PINK-1 in nicotine-dependent neuroprotection. This suggests that nicotines selective protection of substantia nigra DNs is due to the confluence of two factors: first, their unique vulnerability to mitochondrial stress, which is mitigated by increased mitochondrial quality control due to PINK1 activation; and second, to their specific expression of D3 receptors.

neuroscience↗

bioRxiv2020

Tuning Hsp104 specificity to selectively detoxify alpha-synuclein

Hsp104 is an AAA+ protein disaggregase that solubilizes and reactivates proteins trapped in aggregated states. We have engineered potentiated Hsp104 variants to mitigate toxic misfolding of -synuclein, TDP-43, and FUS implicated in fatal neurodegenerative disorders. Though potent disaggregases, these enhanced Hsp104 variants lack substrate specificity, and can have unfavorable off-target effects. Here, to lessen off-target effects, we engineer substrate-specific Hsp104 variants. By altering Hsp104 pore loops that engage substrate, we disambiguate Hsp104 variants that selectively suppress -synuclein toxicity but not TDP-43 or FUS toxicity. Remarkably, -synuclein-specific Hsp104 variants emerge that mitigate -synuclein toxicity via distinct ATPase-dependent mechanisms, involving -synuclein disaggregation or detoxification of -synuclein conformers without disaggregation. Importantly, both types of -synuclein-specific Hsp104 variant reduce dopaminergic neurodegeneration in a C. elegans model of Parkinsons disease more effectively than non-specific variants. We suggest that increasing the substrate specificity of enhanced disaggregases could be applied broadly to tailor therapeutics for neurodegenerative disease.

bioengineering↗

bioRxiv2019

VPS41 recessive mutation causes ataxia and dystonia with retinal dystrophy and mental retardation by inhibiting HOPS function and mTORC1 signaling

The vacuolar protein sorting protein 41 (VPS41) is a neuroprotective protein in models of Parkinsons disease (PD). As part of the HOPS (Homotypic fusion and Protein Sorting) complex, VPS41 regulates fusion of lysosomes with late endosomes and autophagosomes. Independent of HOPS, VPS41 regulates transport of newly synthesized lysosomal membrane proteins and secretory proteins. Here we report two brothers with compound heterozygous mutations in VPS41 (VPS41R662* and VPS41S285P), born to healthy and non-consanguineous parents. Both patients displayed transient retinal dystrophy, ataxia and dystonia, with brain MRI findings of cerebellar atrophy and a thin saber-shape corpus callosum. Patient-derived fibroblasts contained enzymatically active lysosomes that were poorly reached by endocytic cargo and failed to attract the mTORC1 complex. Consequently, transcription factor TFE3, a driver of autophagy and lysosomal genes, showed continuous nuclear localization which resulted in elevated LC3-II levels and an impaired response to nutrient starvation. CRISPR/CAS VPS41 HeLa knockout cells showed a similar phenotype that could be rescued by wildtype VPS41 but not by VPS41S285P or VPS41R662*. mTORC1 inhibition was also seen after knockout of HOPS subunits VPS11 or VPS18. Regulated neuropeptide secretion in PC12 VPS41 knockout cells was rescued by VPS41S285P expression, indicating that this HOPS-independent function was preserved. Co-expression of the VPS41S285P and VPS41R662* variants in a C. elegans model of PD abolished the protective effect of VPS41 against -synuclein-induced neurodegeneration. We conclude that both disease-associated VPS41 variants specifically abrogate HOPS function, which leads to a delay in endocytic cargo delivery to lysosomes, mTORC1 inhibition and irresponsiveness to autophagic clues. Our studies signify a link between HOPS function and mTORC1 signaling and imply that HOPS function is required for the neuroprotective effect of VPS41 in PD.

cell biology↗