Andrey A. Parkhitko

Skeletal muscle loss and functional decline are sexually dimorphic, with fast-twitch type II fibers disproportionately vulnerable to age-related atrophy. DNA damage accumulation is a hallmark of aging whose consequences in myofibers remain poorly understood. Using a type II fiber-specific DNA repair-deficient mouse, we show that the same genotoxic insult produces qualitatively different lesion landscapes by sex, oxidative damage in females and uracil misincorporation in males. Females exhibited greater atrophy pathway activation, paralleling clinical evidence that genotoxic stress disproportionately drives frailty in women. Single- nucleus RNA sequencing and metabolomics identified PDK4 as the key female-specific metabolic driver. Pharmacologic PDK4 inhibition restored oxidative metabolism and myotube health. Dietary α-ketoglutarate, replenishing TCA intermediates downstream of the PDK4 block, rescued contractile force and metabolic profiles in females. Human aging data confirmed conservation of this pathway, revealing a sex-specific mechanism linking DNA damage to metabolic dysfunction and identifying an accessible therapeutic strategy to combat female-predominant frailty.

Animals rely on color to navigate complex environments, yet how eyeless organisms use chromatic information to guide food choice remains poorly understood. Here, we show that Caenorhabditis elegans exhibits robust color-dependent foraging driven by microbial chromophores, preferentially consuming red while avoiding blue chromoprotein-expressing bacteria across bacterial backgrounds and wild isolates. This discrimination persists in darkness and independently of photoreceptor, revealing a mechanism beyond canonical photoreception. Purified chromoproteins and bacterial metabolite fractions independently reproduce preference, demonstrating complementary chromatic and post-ingestive metabolic cues. Mechanistically, blue chromoproteins generate singlet oxygen, producing oxidative stress and remodeling bacterial tryptophan and pterin metabolism, whereas red food promotes serotonin production and feeding-associated neuropeptide signaling. Disrupting serotonin biosynthesis or neuropeptide processing abolishes color preference. Together, our findings reveal a previously unrecognized, novel sensory strategy in which wavelength-selective pigment photochemistry transforms microbial color into metabolic information that is integrated through gut–brain neuroendocrine signaling to guide foraging behavior in an eyeless animal.

Aging involves widespread metabolic dysregulation, including a decline in total nicotinamide adenine dinucleotide (NAD) levels. While NAD precursor supplementation elevates total NAD levels, it does not reveal tissue-specific effects of an altered NADH [reduced form of NAD ⁺ (oxidized NAD)]/NAD ⁺ balance. To address this, we generated transgenic Drosophila expressing the genetically encoded xenotopic enzyme Lb NOX, which converts NADH to NAD ⁺ . Lb NOX expression modulated both NAD(H) and NADP(H) (reduced form of NAD phosphate) metabolites in a sex-dependent manner and rescued neuronal cell death induced by mutant αB-crystallin–associated reductive stress. We demonstrate that tissue-specific targeting of redox NAD metabolism shows distinct outcomes: Muscle-specific Lb NOX expression confers stronger protection against paraquat-induced oxidative stress than whole-body expression, emphasizing tissue-dependent redox sensitivity. Notably, Lb NOX expression in nonneuronal tissues restored youthful sleep patterns in aged flies. Together, these findings establish Lb NOX as an efficient xenotopic tool for in vivo redox manipulation and reveal tissue- and sex-specific NAD(P)H mechanisms underlying aging, stress resilience, and sleep regulation, providing a framework for NAD-based interventions in aging.

Insulin/insulin growth factor signaling is a conserved pathway that regulates lifespan. However, long-lived loss-of-function mutants often produce insulin resistance, slow growth, and impair reproduction. Recently, a gain-of-function mutation in the kinase insert domain (KID) of the Drosophila insulin/IGF receptor was seen to dominantly extend lifespan without impairing insulin sensitivity, growth, or reproduction. This substitution occurs within residues conserved in mammalian insulin receptor (IR) and insulin growth factor-1 receptor (IGF-1R). We produced 2 knock-in mouse strains that carry the homologous KID Arg/Cys substitution in murine IR or IGF-1R, and we replicated these genotypes in human cells. Cells with heterodimer receptors of IR or IGF-1R induce receptor phosphorylation and phospho-Akt when stimulated with insulin or IGF. Heterodimer receptors of IR fully induce pERK, but ERK was less phosphorylated in cells with IGF-1R heterodimers. Adults with a single KID allele (producing heterodimer receptors) have normal growth and glucose regulation. At 4 months, these mice variably display hormonal markers that associate with successful aging counteraction, including elevated adiponectin and FGF21, as well as reduced leptin and IGF-1. Livers of IGF-1R females show decreased transcriptome-based biological age, which may point toward delayed aging and warrants an actual lifespan experiment. These data suggest that KID mutants may slow mammalian aging while they avoid the complications of insulin resistance.

As aging is the primary risk factor for many chronic diseases, geroscience aims to target aging to delay age-related decline. Here, we identify Cyrene (dihydrolevoglucosenone), a sustainable, biocompatible solvent, as a novel geroprotective compound. Cyrene extends lifespan and healthspan in C. elegans , improving locomotor function and resistance to oxidative, thermal, osmotic, genotoxic, and proteotoxic stress. It also confers protection in neurodegenerative models of Alzheimer’s, Parkinson’s, and Huntington’s disease. Cyrene is effective when delivered during development or early adulthood and requires administration before day 8 to extend longevity. Its benefits are independent of bacterial metabolism and partially independent of the FOXO transcription factor DAF-16. Importantly, Cyrene also extends lifespan and enhances oxidative stress resistance in Drosophila melanogaster , demonstrating cross-species efficacy. These findings identify Cyrene as a novel geroprotective compound that promotes longevity, resilience, and neuroprotection. Conservation across species supports future work to dissect molecular mechanisms and test its potential in mammals.

Insulin/insulin growth factor signaling is a conserved pathway that regulates lifespan across many species. Multiple mechanisms are proposed for how this altered signaling slows aging. To elaborate these causes, we recently developed a series of Drosophila insulin-like receptor (dInr) mutants with single amino acid substitutions that extend lifespan but differentially affect insulin sensitivity, growth and reproduction. Transheterozygotes of canonical dInr mutants (Type I) extend longevity and are insulin-resistant, small and weakly fecund. In contrast, a dominant mutation (dInr³⁵³, Type II) within the Kinase Insert Domain (KID) robustly extends longevity but is insulin-sensitive, full-sized, and highly fecund. We applied transcriptome and metabolome analyses to explore how dInr³⁵³ slows aging without insulin resistance. Type I and II mutants overlap in many pathways but also produce distinct transcriptomic profiles that include differences in innate immune and reproductive functions. In metabolomic analyses, the KID mutant dInr³⁵³ reprograms methionine metabolism in a way that phenocopies dietary methionine restriction, in contrast to canonical mutants which are characterized by upregulation of the transsulfuration pathway. Because abrogation of S-adenosylhomocysteine hydrolase blocks the longevity benefit conferred by dInr³⁵³, we conclude the methionine cycle reprogramming of Type II is sufficient to slow aging. Metabolomic analysis further revealed the Type II mutant is metabolically flexible: unlike aged wildtype, aged dInr³⁵³ adults can reroute methionine toward the transsulfuration pathway, while Type I mutant flies upregulate the transsulfuration pathway continuously from young age. Altered insulin/insulin growth factor signaling has the potential to slow aging without the complications of insulin resistance by modulating methionine cycle dynamics.

Aging is associated with dysregulated methionine metabolism and increased levels of enzymes in the tyrosine degradation pathway (TDP). To investigate the efficacy of targeting either methionine metabolism or the TDP for healthspan improvement in advanced age, we initiated dietary MetR or TDP inhibition in 18-month-old C57BL/6J mice. MetR significantly improved neuromuscular function, metabolic health, lung function, and frailty. In addition, we confirmed improved neuromuscular function from dietary MetR in 5XFAD mice, whose weight was not affected by MetR. We did not observe benefits with TDP inhibition. Single-nucleus RNA and ATAC sequencing of muscle revealed cell type–specific responses to MetR, although MetR did not significantly affect mouse aging epigenetic clock markers. Similarly, an 8-week MetR intervention in a human trial (NCT04701346) showed no significant impact on epigenetic clocks. The observed benefits from late-life MetR provide translational rationale to develop MetR mimetics as an antiaging intervention.

Metabolic dysregulation represents one of the major driving forces in aging. Although multiple genetic and pharmacological manipulations are known to extend longevity in model organisms, aging is a complex trait, and targeting one’s own genes may be insufficient to prevent age-dependent deterioration. An alternative strategy could be to use enzymes from other species to reverse age-associated metabolic changes. In this review, we discuss a set of enzymes from lower organisms that have been shown to affect various metabolic parameters linked to age-related processes. These enzymes include modulators of steady-state levels of amino acids (METase, ASNase, and ADI), NADPH/NADP ⁺ and/or reduced form of coenzyme Q (CoQH ₂ )/CoQ redox potentials (NDI1, AOX, Lb NOX, TPNOX, Ec STH, RquA, LOXCAT, Grubraw, and ScURA), GSH (StGshF), mitochondrial membrane potential (mtON and mito-dR), or reactive oxygen species (DAAO and KillerRed-SOD1). We propose that leveraging non-mammalian enzymes represents an untapped resource that can be used to delay aging and age-related diseases.

Insulin/insulin growth factor signaling is a conserved pathway that regulates lifespan across many species. Multiple mechanisms are proposed for how this altered signaling slows aging. To elaborate these causes, we recently developed a series of Drosophila insulin-like receptor ( dInr ) mutants with single amino acid substitutions that extend lifespan but differentially affect insulin sensitivity, growth and reproduction. Transheterozygotes of canonical dInr mutants (Type I) extend longevity and are insulin-resistant, small and weakly fecund. In contrast, a dominant mutation ( dInr ³⁵³ , Type II) within the Kinase Insert Domain (KID) robustly extends longevity but is insulin-sensitive, full-sized, and highly fecund. We applied transcriptome and metabolome analyses to explore how dInr ³⁵³ slows aging without insulin resistance. Type I and II mutants overlap in many pathways but also produce distinct transcriptomic profiles that include differences in innate immune and reproductive functions. In metabolomic analyses, the KID mutant dInr ³⁵³ reprograms methionine metabolism in a way that phenocopies dietary methionine restriction, in contrast to canonical mutants which are characterized by upregulation of the transsulfuration pathway. Because abrogation of S-adenosylhomocysteine hydrolase blocks the longevity benefit conferred by dInr ³⁵³ , we conclude the methionine cycle reprogramming of Type II is sufficient to slow aging. Metabolomic analysis further revealed the Type II mutant is metabolically flexible: unlike aged wildtype, aged dInr ³⁵³ adults can reroute methionine toward the transsulfuration pathway, while Type I mutant flies upregulate the trassulfuration pathway continuously from young age. Altered insulin/insulin growth factor signaling has the potential to slow aging without the complications of insulin resistance by modulating methionine cycle dynamics. Author Summary: Mutations in the invertebrate insulin/IGF signaling system robustly extend lifespan. Yet these interventions often cause insulin resistance, reduce growth, and impair fertility. In contrast, a dominant gain-of-function mutation in the kinase insert domain of the Drosophila insulin/IGF receptor extends lifespan while maintaining insulin sensitivity, growth, or reproduction. Here, we demonstrate this unique mutation reprograms methionine metabolism pathway in a way that mirrors dietary methionine restriction, which is known to extend lifespan in several animals including Drosophila and mice. Genetic epistasis analysis verifies this methionine cycle inhibition is an underlying cause for how the kinase insert domain mutation slows Drosophila aging while maintaining insulin-sensitivity, growth, and fecundity.