Early-life starvation alters lipid metabolism in adults to cause developmental pathology in Caenorhabditis elegans.

Early-life malnutrition increases adult disease risk in humans, but the causal changes in gene regulation, signaling, and metabolism are unclear. In the roundworm Caenorhabditis elegans, early-life starvation causes well-fed larvae to develop germline tumors and other gonad abnormalities as adults. Furthermore, reduced insulin/IGF signaling during larval development suppresses these starvation-induced abnormalities. How early-life starvation and insulin/IGF signaling affect adult pathology is unknown. We show that early-life starvation has pervasive effects on adult gene expression which are largely reversed by reduced insulin/IGF signaling following recovery from starvation. Early-life starvation increases adult fatty-acid synthetase fasn-1 expression in daf-2 insulin/IGF signaling receptor-dependent fashion, and fasn-1/FASN promotes starvation-induced abnormalities. Lipidomic analysis reveals increased levels of phosphatidylcholine in adults subjected to early-life starvation, and supplementation with unsaturated phosphatidylcholine during development suppresses starvation-induced abnormalities. Genetic analysis of fatty-acid desaturases reveals positive and negative effects of desaturation on development of starvation-induced abnormalities. In particular, the ω3 fatty-acid desaturase fat-1 and the Δ5 fatty-acid desaturase fat-4 inhibit and promote development of abnormalities, respectively. fat-4 is epistatic to fat-1, suggesting that arachidonic acid-containing lipids promote development of starvation-induced abnormalities, and supplementation with ARA enhanced development of abnormalities. This work shows that early-life starvation and insulin/IGF signaling converge on regulation of adult lipid metabolism, affecting stem-cell proliferation and tumor formation.

Insulin/IGF-dependent Wnt signaling promotes formation of germline tumors and other developmental abnormalities following early-life starvation in Caenorhabditis elegans.

The Developmental Origins of Health and Disease hypothesis postulates that early-life stressors can predispose people to disease later in life. In the roundworm Caenorhabditis elegans, prolonged early-life starvation causes germline tumors, uterine masses, and other gonad abnormalities to develop in well-fed adults. Reduction of insulin/insulin-like growth factor (IGF) signaling (IIS) during larval development suppresses these starvation-induced abnormalities. However, molecular mechanisms at play in formation and suppression of starvation-induced abnormalities are unclear. Here we describe mechanisms through which early-life starvation and reduced IIS affect starvation-induced abnormalities. Transcriptome sequencing revealed that expression of genes in the Wnt signaling pathway is upregulated in adults starved as young larvae, and that knockdown of the insulin/IGF receptor daf-2/InsR decreases their expression. Reduction of Wnt signaling through RNAi or mutation reduced starvation-induced abnormalities, and hyperactivation of Wnt signaling produced gonad abnormalities in worms that had not been starved. Genetic and reporter-gene analyses suggest that Wnt signaling acts downstream of IIS in the soma to cell-nonautonomously promote germline hyperproliferation. In summary, this work reveals that IIS-dependent transcriptional regulation of Wnt signaling promotes starvation-induced gonad abnormalities, illuminating signaling mechanisms that contribute to adult pathology following early-life starvation.

Genetic analysis of daf-18/PTEN missense mutants for starvation resistance and developmental regulation during Caenorhabditis elegans L1 arrest.

Mutations in the well-known tumor suppressor PTEN are observed in many cancers. PTEN is a dual-specificity phosphatase that harbors lipid and protein-phosphatase activities. The Caenorhabditis elegans PTEN ortholog is daf-18, which has pleiotropic effects on dauer formation, aging, starvation resistance, and development. Function of 3 daf-18 point-mutants, G174E, D137A, and C169S, had previously been investigated using high-copy transgenes in a daf-18 null background. These alleles were generated based on their mammalian counterparts and were treated as though they specifically disrupt lipid or protein-phosphatase activity, or both, respectively. Here, we investigated these alleles using genome editing of endogenous daf-18. We assayed 3 traits relevant to L1 starvation resistance, and we show that each point mutant is essentially as starvation-sensitive as a daf-18 null mutant. Furthermore, we show that G174E and D137A do not complement each other, suggesting overlapping effects on lipid and protein-phosphatase activity. We also show that each allele has strong effects on nucleocytoplasmic localization of DAF-16/FoxO and dauer formation, both of which are regulated by PI3K signaling, similar to a daf-18 null allele. In addition, each allele also disrupts M-cell quiescence during L1 starvation, though D137A has a weaker effect than the other alleles, including the null. Our results confirm that daf-18/PTEN is important for promoting starvation resistance and developmental arrest and that it is a potent regulator of PI3K signaling, and they highlight challenges of using genetic analysis to link specific DAF-18/PTEN enzymatic activities to particular phenotypes.

Insulin/IGF Signaling and Vitellogenin Provisioning Mediate Intergenerational Adaptation to Nutrient Stress.

The roundworm C. elegans reversibly arrests larval development during starvation [1], but extended early-life starvation reduces reproductive success [2, 3]. Maternal dietary restriction (DR) buffers progeny from starvation as young larvae, preserving reproductive success [4]. However, the developmental basis of reduced fertility following early-life starvation is unknown, and it is unclear how maternal diet modifies developmental physiology in progeny. We show here that extended starvation in first-stage (L1) larvae followed by unrestricted feeding results in a variety of developmental abnormalities in the reproductive system, including proliferative germ-cell tumors and uterine masses that express neuronal and epidermal cell fate markers. We found that maternal DR and reduced maternal insulin/insulin-like growth factor (IGF) signaling (IIS) increase oocyte provisioning of vitellogenin lipoprotein, reducing penetrance of starvation-induced abnormalities in progeny, including tumors. Furthermore, we show that maternal DR and reduced maternal IIS reduce IIS in progeny. daf-16/FoxO and skn-1/Nrf, transcriptional effectors of IIS, are required in progeny for maternal DR and increased vitellogenin provisioning to suppress starvation-induced abnormalities. daf-16/FoxO activity in somatic tissues is sufficient to suppress starvation-induced abnormalities, suggesting cell-nonautonomous regulation of reproductive system development. This work reveals that early-life starvation compromises reproductive development and that vitellogenin-mediated intergenerational insulin/IGF-to-insulin/IGF signaling mediates adaptation to nutrient availability.