Guha, Sanjib et al. (2021) International Worm Meeting "The Role of Alzheimer's disease relevant Tau modifications in Neurodegeneration and Mitochondrial dysfunction"

Guha, Sanjib, JOHNSON, GAIL, Nehrke, Keith

[International Worm Meeting, 2021]

Background: Alzheimer's disease (AD) is a progressive neurodegenerative disorder whose pathological hallmarks include intraneuronal neurofibrillary tangles (NFTs) composed of the microtubule-associated protein Tau. Tau isolated from AD brain exhibits abnormally high levels of post-translational modifications (PTMs) including phosphorylation and acetylation at specific epitopes that increase with disease severity and age. In addition, mitochondrial dysfunction is an early feature of AD, and abnormal, toxic tau PTMs may contribute to disease pathogenesis. A major bottleneck in understanding the mechanisms behind the neurotoxicity of pathological forms of Tau is the lack of genetically tractable models that can recapitulate the effects of Tau PTMs in a short time frame without artifacts associated with Tau overexpression. Method: Human 0N4R Tau (wild type) was expressed in touch receptor neurons through single-copy gene insertion. Mutations were introduced into the single-copy tau transgene through CRISPR-Cas9 genome editing, including T231E, to mimic phosphorylation of a commonly observed pathological epitope, and K274/281Q, to mimic disease-associated lysine acetylation. We then assessed their impact on age-dependent response to light touch, neurodegeneration, and mitochondrial parameters such as abundance, morphology, trafficking, and turnover, using fluorescent biosensors including mito-mKeima. Result: Unlike existing tau overexpression models, C. elegans single-copy expression of wild type human tau did not elicit overt pathological phenotypes at baseline. However, strains expressing disease associated PTM-mimetics (T231E and K274/281Q) exhibited reduced touch sensation and neuronal morphological abnormalities that increased with age. Remarkably, the PTM-mimetics selectively impaired mitophagy following mitochondrial oxidative stress, but had no effect on macroautophagy, and furthermore reduced mitolysosomal trafficking. Conclusion: Single copy expression limits pathological phenotypes to strains expressing disease-associated Tau mutants. In addition to overt pathology, these mutants eliminate oxidative stress-induced mitophagy and reduce trafficking of mitolysosomes. Our findings highlight a selective mechanism through which disease-associated Tau PTMs may suppress compensatory responses to mitochondrial stress that occur with age and provide a new perspective into the pathogenic mechanisms underlying AD. Published paper: Guha, S., S. Fischer, G.V.W. Johnson, and K. Nehrke. 2020. Tauopathy-associated tau modifications selectively impact neurodegeneration and mitophagy in a novel C. elegans single-copy transgenic model. Mol Neurodegener. 15(1).

GUHA, SANJIB et al. (2019) International Worm Meeting "Alzheimer's disease relevant Tau modifications aggravate mitochondrial dysfunction and neurodegeneration in novel C. elegans single-copy transgenic models."

JOHNSON, GAIL, Nehrke, Keith, Guha, Sanjib

[International Worm Meeting, 2019]

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common form of dementia. The pathological hallmarks include accumulation of extracellular senile plaques (SP) composed of beta-amyloid protein (Abeta) and intraneuronal neurofibrillary tangles (NFTs) composed of pathological Tau species in several cortical brain regions. The microtubule-associated protein Tau plays a central role in pathogenesis of this disease and it has been reported that Tau isolated from AD brain exhibits a number of abnormal posttranslational modifications (PTMs), including increases in phosphorylation and acetylation at specific epitopes. A major bottleneck in understanding the mechanisms behind the neurotoxicity of pathological forms of tau is the lack of genetically tractable models that can recapitulate the effects of Tau PTMs in a short time frame without artifacts associated with Tau overexpression. To that end, we have generated novel single-copy transgenic Caenorhabditis elegans models using wild type Tau and mutant Tau with AD-relevant, PTM-mimetics introduced through CRISPR-Cas9 gene editing. The animals expressing phosphomimetic or acetylmimetic Tau in touch neurons exhibit several pathological phenotypes such as reduced touch sensation as well as mechanosensory neurodegeneration within two weeks of adulthood. Interestingly, they also demonstrate shortened lifespan. Investigations are ongoing to utilize fluorescent biosensors such as mito-mKeima to interrogate mitophagy and mito-roGFP2 to examine redox stress, two outputs that are thought to be impacted by pathological Tau. These data will further our understanding of how site-specific, AD-relevant PTMs of Tau affect mitochondrial function, stress responses, protein turnover and thus neuronal health.

Bose, Neelanjan et al. (2017) International Worm Meeting "A Caenorhabditis elegans Model to Study Age-related Complications Associated with Diabetes and Parkinson's Disease."

Bose, Neelanjan, Khateeb, Sana, Rifkind, Alexander, Hall, David, Liu, Jianfeng, Guha, Sanjib K., Chaudhuri, Jyotiska, Gong, Jianke, Kapahi, Pankaj, Xu, X. Z. Shawn

[International Worm Meeting, 2017]

Aging and chronic hyperglycemia leads to the accumulation of reactive a-dicarbonyls (a-DCs), like methylglyoxal. a-DCs react rapidly with biological macromolecules, such as proteins, lipid, and DNA to generate Advanced Glycation End-products (AGEs). AGEs can enhance protein aggregation, cause cellular stress and inflammation that have been associated with aging and a number of age-related pathologies, including various forms of diabetic complications and neurodegenerative diseases. Evolutionarily conserved glyoxalases are responsible for a-DC detoxification to limit AGE stress; however their core biochemical regulation have remained unclear. We have established a Caenorhabditis elegans model, based on an impaired glyoxalase (glod-4/GLO1), to broadly study a-DC-related stress. We show that glod-4 animals rapidly exhibit several diabetes-like phenotypes including hyperesthesia, neuronal damage, and early mortality. We further demonstrate that the ion channel TRPA-1 acts as a novel sensor for a-DCs and AGEs, conserved between worms and mammals. Moreover, TRPA-1 activates SKN-1/Nrf2 via calcium-modulated kinase signaling, ultimately regulating the glutathione-dependent (glod-4/GLO1) and -independent (djr-1.1/DJ1 and djr-1.2/DJ1) glyoxalases to detoxify a-DCs and AGEs. We show that TRPA1-Nrf2 pathway is not only relevant for diabetic complications, but also provide protection against dopaminergic neuronal damage in C. elegans, as observed in Parkinson's disease (PD). We also show that synthetic AGE supplementation is sufficient to recapitulate significating diabetic and PD patholgies both in worms and mamalian systems. Finally, a phenotypic drug-screen using C. elegans identified podocarpic acid as an novel activator of TRPA-1 that rescues both diabetes and PD-related pathologies in C. elegans and mammalian cells. We propose that the upstream amelioration of a-DC stress represents a viable option to address related pathologies in diabetes and associated neurodegenerative conditions such as PD.

Chaudhuri, Jyotiska et al. (2017) International Worm Meeting "Role of Advance Glycation End products (AGEs) in modulating Caenorhabditis elegans feeding behavior."

Sarpong, Richmond, Bose, Neelanjan, Lim, Austin, Sawano, Shota, Kapahi, Pankaj, Chaudhuri, Jyotiska, Guha, Sanjib, Hodge, Brian, Ronnen-Oron , Tal, Lucanic, Mark, Lithgow, Gordon, Hall, David, Chamoli, Manish

[International Worm Meeting, 2017]

Advanced Glycation End products (AGEs) have been implicated in a plethora of diseases including diabetic complications. In an earlier study, we have established a Caenorhabditis elegans mutant that accumulate a- dicarbonyls, the precursor of AGEs, as a model to study diabetes related neuronal damage. Recent RNAseq analyses of this mutant suggest significant differential expression of genes regulating processes such as fat metabolism, neurotransmission etc. that could potentially be mediated by AGEs. Preliminary data on this mutant also suggests that they exhibit enhanced rate of feeding. Supplementation of synthetic AGEs to the diet exacerbates this feeding phenotype in wild type animals early in life, resulting in pan-neuronal damage, accumulation of fat and shortening of lifespan. Therefore, we hypothesize that regulation of food intake could be modulated by alteration in AGE-mediated neurotransmission that could affect the feeding behavior related genes. This is a mechanism which is still poorly understood that could potentially impact diabetes related obesity and other complications.