Caenorhabditis elegans DAF-2 as a Model for Human Insulin Receptoropathies

Insulin receptor variants: Extending the traditional Mendelian spectrum

PURPOSE

INSR encodes the insulin receptor, the essential entrainer of growth and metabolism to nutritional cues. INSR variants cause a spectrum of monogenic insulin resistance (IR) syndromes, namely, type A insulin resistance, Rabson-Mendenhall, and Donohue syndromes. However, to our knowledge, no large cohort studies focused on variant classification and its diagnostic value have been described.

METHODS

This multicentric cohort study included 73 patients carrying INSR variants, referred for IR by 52 centers from 6 countries. Variants were classified using new bioinformatic tools relying on different prediction mechanisms and the American College of Medical Genetics and Genomics guidelines.

RESULTS

Besides expanding the INSR mutational spectrum, this study suggested a semidominant inheritance in several Donohue/Rabson-Mendenhall syndrome families. Questioning strictly Mendelian inheritance, heterozygous loss-of-function (LoF) variants were mostly found in overweight patients, with a higher LoF frequency in IR patients than in the general population (odds ratio 5.77). Diagnostic challenges arose when trying to refine classification criteria for variants of uncertain significance. Among the variant effect predictors assessed, MISTIC and AlphaMissense outperformed REVEL.

CONCLUSION

The spectrum of INSR-related disorders extends beyond traditional entities. Heterozygous INSR LoF variants may increase IR susceptibility. International collaboration and functional assays are needed to drive precision medicine forward.

A comprehensive approach, based on the use of Caenorhabditis elegans, mouse, and human models, elucidates the impact of Lactiplantibacillus plantarum TWK10 on exercise performance and longevity

The functionality of probiotics is highly influenced by culture and processing conditions, making batch stability validation through human or mouse trials impractical. Here, we employed a comprehensive approach using Caenorhabditis elegans, mouse and human models to elucidate the beneficial effects of Lactiplantibacillus plantarum TWK10 (TWK10). In C. elegans, TWK10 administration significantly prolonged lifespan by 26.1 ± 11.9 % (p < 0.05), enhanced locomotion (p < 0.01) and muscle mass (p < 0.001), elevated glycogen storage (p < 0.05), and reduced lipid accumulation (p < 0.001), outperforming Lacticaseibacillus rhamnosus GG and L. plantarum type strain ATCC 14917T. We also confirmed the equivalence of laboratory-prepared and mass-produced TWK10 in ergogenic efficacy using C. elegans assay. In mice, oral administration of mass-produced TWK10 significantly enhanced exercise performance and glycogen storage in muscle and liver in a dose-dependent manner. In a clinical study involving healthy male adults, significant improvements in grip strength (1.1-fold, p < 0.01) and exhaustion time (1.27-fold, p < 0.01), and significant reductions in circulating lactate and ammonia levels were observed in the TWK10 group (1 × 1010 colony-forming unit/day) compared to the control group. Both humans and mice receiving mass-produced TWK10 showed improved body composition with increased muscle mass and reduced fat mass. In conclusion, TWK10 demonstrates superior longevous and ergogenic effects in C. elegans compared to reference strains. The consistent ergogenic efficacy of mass-produced TWK10 across C. elegans, mice, and humans, highlights the utility of C. elegans as a reliable model for probiotic research and industrial application.

Catalytic activities of wild-type C. elegans DAF-2 kinase and dauer-associated mutants

DAF-2, the Caenorhabditis elegans insulin-like receptor homolog, regulates larval development, metabolism, stress response, and lifespan. The availability of numerous daf-2 mutant alleles has made it possible to elucidate the genetic mechanisms underlying these physiological processes. The DAF-2 pathway is significantly conserved with the human insulin/IGF-1 signaling pathway; it includes proteins homologous to human IRS, GRB-2, and PI3K, making it an important model to investigate human pathological conditions. We expressed and purified the kinase domain of wild-type DAF-2 to examine the catalytic activity and substrate specificity of the enzyme. Like the human insulin receptor kinase, DAF-2 kinase phosphorylates tyrosines within specific YxN or YxxM motifs, which are important for recruiting downstream effectors. DAF-2 kinase phosphorylated peptides derived from the YxxM and YxN motifs located in the C-terminal extension of the receptor tyrosine kinase, consistent with the idea that the DAF-2 receptor may possess independent signaling capacity. Unlike the human insulin or IGF-1 receptor kinases, DAF-2 kinase was poorly inhibited by the small-molecule inhibitor linsitinib. We also expressed and purified mutant kinases corresponding to daf-2 alleles that result in partial loss-of-function phenotypes in C. elegans. These mutations caused a complete loss of kinase function in vitro. Our biochemical investigations provide new insights into DAF-2 kinase function, and the approach should be useful for studying other mutations to shed light on DAF-2 signaling in C. elegans physiology.

The ACE inhibitor captopril inhibits ACN-1 to control dauer formation and aging

The renin-angiotensin-aldosterone system (RAAS) plays a well-characterized role regulating blood pressure in mammals. Pharmacological and genetic manipulation of the RAAS has been shown to extend lifespan in Caenorhabditis elegans, Drosophila and rodents, but its mechanism is not well defined. Here, we investigate the angiotensin-converting enzyme (ACE) inhibitor drug captopril, which extends lifespan in worms and mice. To investigate the mechanism, we performed a forward genetic screen for captopril-hypersensitive mutants. We identified a missense mutation that causes a partial loss of function of the daf-2 receptor tyrosine kinase gene, a powerful regulator of aging. The homologous mutation in the human insulin receptor causes Donohue syndrome, establishing these mutant worms as an invertebrate model of this disease. Captopril functions in C. elegans by inhibiting ACN-1, the worm homolog of ACE. Reducing the activity of acn-1 via captopril or RNA interference promoted dauer larvae formation, suggesting that acn-1 is a daf gene. Captopril-mediated lifespan extension was abrogated by daf-16(lf) and daf-12(lf) mutations. Our results indicate that captopril and acn-1 influence lifespan by modulating dauer formation pathways. We speculate that this represents a conserved mechanism of lifespan control.

The ACE-inhibitor drug captopril inhibits ACN-1 to control dauer formation and aging

The renin-angiotensin-aldosterone system (RAAS) plays a well-characterized role regulating blood pressure in mammals. Pharmacological and genetic manipulation of the RAAS has been shown to extend lifespan in C. elegans , Drosophila , and rodents, but its mechanism is not well defined. Here we investigate the angiotensin-converting enzyme (ACE) inhibitor drug captopril, which extends lifespan in worms and mice. To investigate the mechanism, we performed a forward genetic screen for captopril hypersensitive mutants. We identified a missense mutation that causes a partial loss-of-function of the daf-2 receptor tyrosine kinase gene, a powerful regulator of aging. The homologous mutation in the human insulin receptor causes Donohue syndrome, establishing these mutant worms as an invertebrate model of this disease. Captopril functions in C. elegans by inhibiting ACN-1, the worm homolog of ACE. Reducing the activity of acn-1 via captopril or RNAi promoted dauer larvae formation, suggesting acn-1 is a daf gene. Captopril-mediated lifespan extension xwas abrogated by daf-16(lf) and daf-12(lf) mutations. Our results indicate that captopril and acn-1 control aging by modulating dauer formation pathways. We speculate that this represents a conserved mechanism of lifespan control.

Summary Statement

Captopril and acn-1 control aging. By demonstrating they regulate dauer formation and interact with daf genes, including a new DAF-2(A261V) mutant corresponding to a human disease variant, we clarified the mechanism.

PM2.5 induce lifespan reduction, insulin/IGF-1 signaling pathway disruption and lipid metabolism disorder in Caenorhabditis elegans

Introduction

Exposure to fine particulate matter (PM), especially PM2.5, can induce various adverse health effects in populations, including diseases and premature death, but the mechanism of its toxicity is largely unknown.

Methods

Water-soluble components of PM2.5 (WS-PM2.5) were collected in the north of China in winter, and combined in two groups with the final concentrations of 94 μg/mL (CL group, AQI ≤ 100) and 119 μg/mL (CH group, 100 < AQI ≤ 200), respectively. The acute and long-term toxic effects of WS-PM2.5 samples were evaluated in several aspects such as development, lifespan, healthspan (locomotion behavior, heat stress tolerance, lipofucin). DAF mutants and genes were applied to verify the action of IIS pathway in WS-PM2.5 induced-effects. RNA-Sequencing was performed to elucidate the molecular mechanisms, as well as ROS production and Oil red O staining were also served as means of mechanism exploration.

Results

Body length and lifespan were shortened by exposure to WS-PM2.5. Healthspan of nematodes revealed adverse effects evaluated by head thrash, body bend, pharyngeal pump, as well as intestinal lipofuscin accumulation and survival time under heat stress. The abbreviated lifespan of daf-2(e1370) strain and reduced expression level of daf-16 and hsp-16.2 indicated that IIS pathway might be involved in the mechanism. Thirty-five abnormally expressed genes screened out by RNA-Sequencing techniques, were functionally enriched in lipid/lipid metabolism and transport, and may contribute substantially to the regulation of PM2.5 induced adverse effects in nematodes.

Conclusion

WS-PM2.5 exposure induce varying degrees of toxic effects, such as body development, shorten lifespan and healthspan. The IIS pathway and lipid metabolism/transport were disturbed by WS-PM2.5 during WS-PM2.5 exposure, suggesting their regulatory role in lifespan determination.

Balancer-assisted outcrossing to remove unwanted background mutations

Whole-genome sequencing analysis allows us to identify a large number of natural variants and genetic changes created by mutagenesis. For instance, the Million Mutation Project isolated many point mutant alleles, which are available from the Caenorhabditis Genetics Center. Although collections of such mutations are very useful for genetic studies, the strains are often sick because they have multiple other mutations than the mutation of interest. To utilize the strains, it is necessary to outcross with other strains to remove undesired mutations. We previously constructed an inversion balancer toolkit covering a large part of C. elegans genome. In contrast to classical translocation balancers that cover parts of two chromosomes, each balancer from the toolkit covers a part of a chromosome. We think this compactness is beneficial for outcrossing mutants containing multiple background mutations. Here, we show that the fluorescence inversion balancer can be practically useful for outcrossing in the case where researchers want to simply evaluate the phenotypes.

A Receptor Tyrosine Kinase Network Regulates Neuromuscular Function in Response to Oxidative Stress in Caenorhabditis elegans

The transcription factor Nrf2 plays a critical role in the organism-wide regulation of the antioxidant stress response. The Nrf2 homolog SKN-1 functions in the intestinal cells nonautonomously to negatively regulate neuromuscular junction (NMJ) function in Caenorhabditis elegans To identify additional molecules that mediate SKN-1 signaling to the NMJ, we performed a candidate screen for suppressors of aldicarb resistance caused by acute treatment with the SKN-1 activator arsenite. We identified two receptor tyrosine kinases, EGL-15 (fibroblast growth factor receptor, FGFR) and DAF-2 (insulin-like peptide receptor), that are required for NMJ regulation in response to stress. Through double-mutant analysis, we found that EGL-15 functions downstream of, or parallel to, SKN-1 and SPHK-1 (sphingosine kinase), and that the EGL-15 ligand EGL-17 FGF and canonical EGL-15 effectors are required for oxidative stress-mediated regulation of NMJ function. DAF-2 also functions downstream of or parallel to SKN-1 to regulate NMJ function. Through tissue-specific rescue experiments, we found that FGFR signaling functions primarily in the hypodermis, whereas insulin-like peptide receptor signaling is required in multiple tissues. Our results support the idea that the regulation of NMJ function by SKN-1 occurs via a complex organism-wide signaling network involving receptor tyrosine kinase signaling in multiple tissues.

CRISPR-Cas9 human gene replacement and phenomic characterization in Caenorhabditis elegans to understand the functional conservation of human genes and decipher variants of uncertain significance

Our ability to sequence genomes has vastly surpassed our ability to interpret the genetic variation we discover. This presents a major challenge in the clinical setting, where the recent application of whole-exome and whole-genome sequencing has uncovered thousands of genetic variants of uncertain significance. Here, we present a strategy for targeted human gene replacement and phenomic characterization, based on CRISPR-Cas9 genome engineering in the genetic model organism Caenorhabditis elegans, that will facilitate assessment of the functional conservation of human genes and structure-function analysis of disease-associated variants with unprecedented precision. We validate our strategy by demonstrating that direct single-copy replacement of the C. elegans ortholog (daf-18) with the critical human disease-associated gene phosphatase and tensin homolog (PTEN) is sufficient to rescue multiple phenotypic abnormalities caused by complete deletion of daf-18, including complex chemosensory and mechanosensory impairments. In addition, we used our strategy to generate animals harboring a single copy of the known pathogenic lipid phosphatase inactive PTEN variant (PTEN-G129E), and showed that our automated in vivo phenotypic assays could accurately and efficiently classify this missense variant as loss of function. The integrated nature of the human transgenes allows for analysis of both homozygous and heterozygous variants and greatly facilitates high-throughput precision medicine drug screens. By combining genome engineering with rapid and automated phenotypic characterization, our strategy streamlines the identification of novel conserved gene functions in complex sensory and learning phenotypes that can be used as in vivo functional assays to decipher variants of uncertain significance.

The Ubiquitin Ligase CHIP Integrates Proteostasis and Aging by Regulation of Insulin Receptor Turnover

Aging is attended by a progressive decline in protein homeostasis (proteostasis), aggravating the risk for protein aggregation diseases. To understand the coordination between proteome imbalance and longevity, we addressed the mechanistic role of the quality-control ubiquitin ligase CHIP, which is a key regulator of proteostasis. We observed that CHIP deficiency leads to increased levels of the insulin receptor (INSR) and reduced lifespan of worms and flies. The membrane-bound INSR regulates the insulin and IGF1 signaling (IIS) pathway and thereby defines metabolism and aging. INSR is a direct target of CHIP, which triggers receptor monoubiquitylation and endocytic-lysosomal turnover to promote longevity. However, upon proteotoxic stress conditions and during aging, CHIP is recruited toward disposal of misfolded proteins, reducing its capacity to degrade the INSR. Our study indicates a competitive relationship between proteostasis and longevity regulation through CHIP-assisted proteolysis, providing a mechanistic concept for understanding the impact of proteome imbalance on aging.

•

The ubiquitin ligase CHIP triggers insulin receptor turnover

•

Insulin receptor level is linked to insulin and IGF1 signaling and longevity

•

Engagement of CHIP in protein quality control limits insulin receptor degradation

•

Proteotoxic stress aggravates insulin receptor stability, drives aging, and shortens lifespan