Browsing by Author "Berkowitz, Laura A."

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    ApoE-associated modulation of neuroprotection from A beta-mediated neurodegeneration in transgenic Caenorhabditis elegans
    (Company of Biologists, 2019) Griffin, Edward F.; Scopel, Samuel E.; Stephen, Cayman A.; Holzhauer, Adam C.; Vaji, Madeline A.; Tuckey, Ryan A.; Berkowitz, Laura A.; Caldwell, Kim A.; Caldwell, Guy A.; University of Alabama Tuscaloosa; University of Alabama Birmingham
    Allele-specific distinctions in the human apolipoprotein E (APOE) locus represent the best-characterized genetic predictor of Alzheimer's disease (AD) risk. Expression of isoform APOE epsilon 2 is associated with reduced risk, while APOE epsilon 3 is neutral and APOE epsilon 4 carriers exhibit increased susceptibility. Using Caenorhabditis elegans, we generated a novel suite of humanized transgenic nematodes to facilitate neuronal modeling of amyloid-beta peptide (A beta) co-expression in the context of distinct human APOE alleles. We found that co-expression of human APOE epsilon 2 with A beta attenuated A beta-induced neurodegeneration, whereas expression of the APOE epsilon 4 allele had no effect on neurodegeneration, indicating a loss of neuroprotective capacity. Notably, the APOE epsilon 3 allele displayed an intermediate phenotype; it was not neuroprotective in young adults but attenuated neurodegeneration in older animals. There was no functional impact from the three APOE isoforms in the absence of A beta co-expression. Pharmacological treatment that examined neuroprotective effects of APOE alleles on calcium homeostasis showed allele-specific responses to changes in ER-associated calcium dynamics in the A beta background. Additionally, A beta suppressed survival, an effect that was rescued by APOE epsilon 2 and APOE epsilon 3, but not APOE epsilon 4. Expression of the APOE alleles in neurons, independent of A beta, exerted no impact on survival. Taken together, these results illustrate that C. elegans provides a powerful in vivo platform with which to explore how AD-associated neuronal pathways are modulated by distinct APOE gene products in the context of A beta-associated neurotoxicity. The significance of both ApoE and A beta to AD highlights the utility of this new pre-clinical model as a means to dissect their functional inter-relationship.
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    Attenuation of Dopaminergic Neurodegeneration in a C. elegans Parkinson's Model through Regulation of Xanthine Dehydrogenase (XDH-1) Expression by the RNA Editase, ADR-2
    (MDPI, 2023) Starr, Lindsey A.; McKay, Luke E.; Peter, Kylie N.; Seyfarth, Lena M.; Berkowitz, Laura A.; Caldwell, Kim A.; Caldwell, Guy A.; University of Alabama Tuscaloosa; University of Alabama Birmingham
    Differential RNA editing by adenosine deaminases that act on RNA (ADARs) has been implicated in several neurological disorders, including Parkinson's disease (PD). Here, we report results of a RNAi screen of genes differentially regulated in adr-2 mutants, normally encoding the only catalytically active ADAR in Caenorhabditis elegans, ADR-2. Subsequent analysis of candidate genes that alter the misfolding of human alpha-synuclein (alpha-syn) and dopaminergic neurodegeneration, two PD pathologies, reveal that reduced expression of xdh-1, the ortholog of human xanthine dehydrogenase (XDH), is protective against alpha-synuclein-induced dopaminergic neurodegeneration. Further, RNAi experiments show that WHT-2, the worm ortholog of the human ABCG2 transporter and a predicted interactor of XDH-1, is the rate-limiting factor in the ADR-2, XDH-1, WHT-2 system for dopaminergic neuroprotection. In silico structural modeling of WHT-2 indicates that the editing of one nucleotide in the wht-2 mRNA leads to the substitution of threonine with alanine at residue 124 in the WHT-2 protein, changing hydrogen bonds in this region. Thus, we propose a model where wht-2 is edited by ADR-2, which promotes optimal export of uric acid, a known substrate of WHT-2 and a product of XDH-1 activity. In the absence of editing, uric acid export is limited, provoking a reduction in xdh-1 transcription to limit uric acid production and maintain cellular homeostasis. As a result, elevation of uric acid is protective against dopaminergic neuronal cell death. In turn, increased levels of uric acid are associated with a decrease in ROS production. Further, downregulation of xdh-1 is protective against PD pathologies because decreased levels of XDH-1 correlate to a concomitant reduction in xanthine oxidase (XO), the form of the protein whose by-product is superoxide anion. These data indicate that modifying specific targets of RNA editing may represent a promising therapeutic strategy for PD.
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    Systemic RNA Interference Defective (SID) genes modulate dopaminergic neurodegeneration in C. elegans
    (PLOS, 2022) Gaeta, Anthony L.; Nourse, J. Brucker, Jr.; Willicott, Karolina; Mckay, Luke E.; Keogh, Candice M.; Peter, Kylie; Russell, Shannon N.; Hamamichi, Shusei; Berkowitz, Laura A.; Caldwell, Kim A.; Caldwell, Guy A.; University of Alabama Tuscaloosa; University of Alabama Birmingham; Tottori University
    The fine-tuning of gene expression is critical for all cellular processes; aberrations in this activity can lead to pathology, and conversely, resilience. As their role in coordinating organismal responses to both internal and external factors have increasingly come into focus, small non-coding RNAs have emerged as an essential component to disease etiology. Using Systemic RNA interference Defective (SID) mutants of the nematode Caenorhabditis elegans, deficient in gene silencing, we examined the potential consequences of dysfunctional epigenomic regulation in the context of Parkinson's disease (PD). Specifically, the loss of either the sid-1 or sid-3 genes, which encode a dsRNA transporter and an endocytic regulatory non-receptor tyrosine kinase, respectively, conferred neuroprotection to dopaminergic (DA) neurons in an established transgenic C. elegans strain wherein overexpression of human alpha-synuclein (alpha-syn) from a chromosomally integrated multicopy transgene causes neurodegeneration. We further show that knockout of a specific microRNA, mir-2, attenuates alpha-syn neurotoxicity; suggesting that the native targets of mir-2-dependent gene silencing represent putative neuroprotective modulators. In support of this, we demonstrated that RNAi knockdown of multiple mir-2 targets enhanced alpha-syn-induced DA neurodegeneration. Moreover, we demonstrate that mir-2 overexpression originating in the intestine can induce neurodegeneration of DA neurons, an effect that was reversed by pharmacological inhibition of SID-3 activity. Interestingly, sid-1 mutants retained mir-2-induced enhancement of neurodegeneration. Transcriptomic analysis of alpha-syn animals with and without a sid-1 mutation revealed 27 differentially expressed genes with human orthologs related to a variety of diseases, including PD. Among these was pgp-8, encoding a P-glycoprotein-related ABC transporter. Notably, sid-1; pgp-8 double mutants abolished the neurodegeneration resulting from intestinal mir-2 overexpression. This research positions known regulators of small RNA-dependent gene silencing within a framework that facilitates mechanistic evaluation of epigenetic responses to exogenous and endogenous factors influencing DA neurodegeneration, revealing a path toward new targets for therapeutic intervention of PD.