The C. elegans truncated insulin receptor DAF-2B regulates survival of L1 arrested larvae.

We have previously characterized a truncated isoform of the C. elegans insulin-like receptor, DAF-2B, which retains the ligand binding domain but cannot transduce a signal due to the absence of the intracellular signaling domain. DAF-2B modifies insulin / insulin-like growth factor signaling-dependent processes, such as dauer formation and lifespan, by sequestering insulin-like peptides (ILP) and preventing signaling through full length DAF-2 receptors. Here we show that DAF-2B is also important for starvation resistance, as genetic loss of daf-2b reduces survival in arrested first stage larvae (L1). Under fed conditions, we observe daf-2b splicing capacity in both the intestine and the hypodermis, but in starved L1s this becomes predominantly hypodermal. Using a novel splicing reporter system, we observe an increase in the ratio of truncated to full length insulin receptor splicing capacity in starved L1 larvae compared with fed, that may indicate a decrease in whole body insulin responsiveness. Consistent with this, overexpression of DAF-2B from the hypodermis, but not the intestine, confers increased survival to L1 animals under starvation conditions. Our findings demonstrate that the truncated insulin receptor DAF-2B is involved in the response to L1 starvation and promotes survival when expressed from the hypodermis.

The SR protein RSP-2 influences expression of the truncated insulin receptor DAF-2B in Caenorhabditis elegans.

The alternatively spliced daf-2b transcript in Caenorhabditis elegans encodes a truncated isoform of the nematode insulin receptor that retains the extracellular ligand binding domain but lacks the intracellular signaling domain and is therefore unable to transduce a signal. To identify factors that influence expression of daf-2b, we performed a targeted RNA interference screen of rsp genes, which encode splicing factors from the serine/arginine protein family. Loss of rsp-2 significantly increased the expression of a fluorescent daf-2b splicing reporter, as well as increasing expression of endogenous daf-2b transcripts. Correspondingly, rsp-2 mutants exhibited similar phenotypes to those previously observed with DAF-2B overexpression, namely suppression of pheromone-induced dauer formation, enhancement of dauer entry in insulin signaling mutants, inhibition of dauer recovery, and increased lifespan. However, the epistatic relationship between rsp-2 and daf-2b varied according to the experimental context. Increased dauer entry and delayed dauer exit of rsp-2 mutants in an insulin signaling mutant background were partially dependent on daf-2b. Conversely, suppression of pheromone-induced dauer formation and increased lifespan in rsp-2 mutants were independent of daf-2b. These data demonstrate that C. elegans RSP-2, an ortholog of human splicing factor protein SRSF5/SRp40, is involved in regulating the expression of the truncated DAF-2B isoform. However, we also find that RSP-2 can influence dauer formation and lifespan independently of DAF-2B.

The positive association between physical activity and alcohol use in African American adults.

African Americans have highest incidence and mortality from obesity-related cancers. Physical activity (PA), minimal alcohol use, and maintaining a low body mass index (BMI) are important cancer prevention behaviors, though there is little research on how these behaviors are associated with one another in African Americans. The purpose of this study is to assess the relationship between PA, alcohol use, and BMI using secondary data from an African American cohort recruited from Houston-area churches. Self-administered questionnaires measured self-reported PA, alcohol use, height, weight, and sociodemographic factors. Univariate and multivariable analyses assessed the relation between PA, alcohol use, BMI, controlling for covariates. Participants (N = 1009) were mostly female (77%), employed (72%), and college graduates (55%). Most (53%) reported both light-to-moderate alcohol use & moderate-to-high levels of PA. There was a statistically significant positive linear association between PA and alcohol use (Pearson's r = 0.15, p < 0.001). We also found that every one hour increase per week in PA was associated with 3% increased odds of being a heavy drinker (>2 drinks/day men, >1 drink/day women), as compared to an abstainer (Adjusted OR = 1.03, 95%CI 1.01-1.06). There was a statistically significant inverse association between PA and BMI, but no statistically significant association between alcohol use and BMI. In this sample of African Americans, PA and alcohol use were positively associated, mirroring results among Non-Hispanic Whites. However, alcohol use and BMI were not statistically significantly associated. Cancer and obesity prevention for African Americans should stress PA promotion while emphasizing messaging to curtail any associated increases in alcohol use.

An alternatively spliced, non-signaling insulin receptor modulates insulin sensitivity via insulin peptide sequestration in C. elegans.

In the nematode C. elegans, insulin signaling regulates development and aging in response to the secretion of numerous insulin peptides. Here, we describe a novel, non-signaling isoform of the nematode insulin receptor (IR), DAF-2B, that modulates insulin signaling by sequestration of insulin peptides. DAF-2B arises via alternative splicing and retains the extracellular ligand binding domain but lacks the intracellular signaling domain. A daf-2b splicing reporter revealed active regulation of this transcript through development, particularly in the dauer larva, a diapause stage associated with longevity. CRISPR knock-in of mScarlet into the daf-2b genomic locus confirmed that DAF-2B is expressed in vivo and is likely secreted. Genetic studies indicate that DAF-2B influences dauer entry, dauer recovery and adult lifespan by altering insulin sensitivity according to the prevailing insulin milieu. Thus, in C. elegans alternative splicing at the daf-2 locus generates a truncated IR that fine-tunes insulin signaling in response to the environment.

Dysregulation of the Mitochondrial Unfolded Protein Response Induces Non-Apoptotic Dopaminergic Neurodegeneration in C. elegans Models of Parkinson's Disease.

Due to environmental insult or innate genetic deficiency, protein folding environments of the mitochondrial matrix are prone to dysregulation, prompting the activation of a specific organellar stress-response mechanism, the mitochondrial unfolded protein response (UPRMT). In Caenorhabditis elegans, mitochondrial damage leads to nuclear translocation of the ATFS-1 transcription factor to activate the UPRMT After short-term acute stress has been mitigated, the UPRMT is eventually suppressed to restore homeostasis to C. elegans hermaphrodites. In contrast, and reflective of the more chronic nature of progressive neurodegenerative disorders such as Parkinson's disease (PD), here, we report the consequences of prolonged, cell-autonomous activation of the UPRMT in C. elegans dopaminergic neurons. We reveal that neuronal function and integrity decline rapidly with age, culminating in activity-dependent, non-apoptotic cell death. In a PD-like context wherein transgenic nematodes express the Lewy body constituent protein α-synuclein (αS), we not only find that this protein and its PD-associated disease variants have the capacity to induce the UPRMT, but also that coexpression of αS and ATFS-1-associated dysregulation of the UPRMT synergistically potentiate dopaminergic neurotoxicity. This genetic interaction is in parallel to mitophagic pathways dependent on the C. elegans PINK1 homolog, which is necessary for cellular resistance to chronic malfunction of the UPRMT Given the increasingly recognized role of mitochondrial quality control in neurodegenerative diseases, these studies illustrate, for the first time, an insidious aspect of mitochondrial signaling in which the UPRMT pathway, under disease-associated, context-specific dysregulation, exacerbates disruption of dopaminergic neurons in vivo, resulting in the neurodegeneration characteristic of PD.SIGNIFICANCE STATEMENT Disruptions or alterations in the activation of pathways that regulate mitochondrial quality control have been linked to neurodegenerative diseases due in part to the central role of mitochondria in metabolism, ROS regulation, and proteostasis. The extent to which these pathways, including the mitochondrial unfolded protein response (UPRMT) and mitophagy, are active may predict severity and progression of these disorders, as well as sensitivity to compounding stressors. Furthermore, therapeutic strategies that aim to induce these pathways may benefit from increased study into cellular responses that arise from long-term or ectopic stimulation, especially in neuronal compartments. By demonstrating the detrimental consequences of prolonged cellular activation of the UPRMT, we provide evidence that this pathway is not a universally beneficial mechanism because dysregulation has neurotoxic consequences.

C. elegans as a model system to accelerate discovery for Parkinson disease.

The nematode Caenorhabditis elegans possesses a wealth of opportunities to explore mechanisms which regulate metazoan complexity, basic cellular biology, and neuronal system attributes. Together, these provide a basis for tenable understanding of neurodegenerative disorders such as Parkinson disease (PD) through functional genomic analysis and pharmacological manipulation for the discovery of previously unknown genetic and environmental risk factors. The application of C. elegans has proven prescient in terms of the elucidation of functional effectors of cellular mechanisms underlying PD that translate to mammals. The current state of PD research using C. elegans encompasses defining obscure combinatorial interactions between genes or between genes and the environment, and continues to provide opportunities for the discovery of new therapeutic targets and disease-modifying drugs.

Potentiated Hsp104 variants antagonize diverse proteotoxic misfolding events.

There are no therapies that reverse the proteotoxic misfolding events that underpin fatal neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). Hsp104, a conserved hexameric AAA+ protein from yeast, solubilizes disordered aggregates and amyloid but has no metazoan homolog and only limited activity against human neurodegenerative disease proteins. Here, we reprogram Hsp104 to rescue TDP-43, FUS, and α-synuclein proteotoxicity by mutating single residues in helix 1, 2, or 3 of the middle domain or the small domain of nucleotide-binding domain 1. Potentiated Hsp104 variants enhance aggregate dissolution, restore proper protein localization, suppress proteotoxicity, and in a C. elegans PD model attenuate dopaminergic neurodegeneration. Potentiating mutations reconfigure how Hsp104 subunits collaborate, desensitize Hsp104 to inhibition, obviate any requirement for Hsp70, and enhance ATPase, translocation, and unfoldase activity. Our work establishes that disease-associated aggregates and amyloid are tractable targets and that enhanced disaggregases can restore proteostasis and mitigate neurodegeneration.