Differential Dose- and Tissue-Dependent Effects of foxo on Aging, Metabolic and Proteostatic Pathways

Abstract

Aging is the gradual deterioration of physiological functions that culminates in death. Several studies across a wide range of model organisms have revealed the involvement of FOXO (forkhead box, class O) transcription factors in orchestrating metabolic homeostasis, as well as in regulating longevity. To study possible dose- or tissue-dependent effects of sustained foxo overexpression, we utilized two different Drosophila transgenic lines expressing high and relatively low foxo levels and overexpressed foxo, either ubiquitously or in a tissue-specific manner. We found that ubiquitous foxo overexpression (OE) accelerated aging, induced the early onset of age-related phenotypes, increased sensitivity to thermal stress, and deregulated metabolic and proteostatic pathways; these phenotypes were more intense in transgenic flies expressing high levels of foxo. Interestingly, there is a defined dosage of foxo OE in muscles and cardiomyocytes that shifts energy resources into longevity pathways and thus ameliorates not only tissue but also organismal age-related defects. Further, we found that foxo OE stimulates in an Nrf2/cncC dependent-manner, counteracting proteostatic pathways, e.g., the ubiquitin-proteasome pathway, which is central in ameliorating the aberrant foxo OE-mediated toxicity. These findings highlight the differential dose- and tissue-dependent effects of foxo on aging, metabolic and proteostatic pathways, along with the foxo-Nrf2/cncC functional crosstalk.

Characteristic Hallmarks of Aging and the Impact on Carcinogenesis

“…Since advanced glycation end products accumulate during aging and age-associated diseases, a recent study demonstrated, by using quantitative proteomics, that protein glycation triggers a proteotoxic response and indirectly affects the protein degradation machinery regulating the cellular function compromised during aging [107]. An interesting article demonstrated that FOXO (forkhead box, class O) transcription factors regulate metabolic homeostasis as well as longevity using Drosophila transgenic lines expressing high and relatively low foxo levels and overexpressed foxo, either ubiquitously or in a tissue-specific manner [108]. Ubiquitous foxo overexpression accelerates aging inducing the early onset of age-related phenotypes, increasing the sensitivity to thermal stress, and deregulating metabolic and proteostatic pathways.…”

“…Ubiquitous foxo overexpression accelerates aging inducing the early onset of age-related phenotypes, increasing the sensitivity to thermal stress, and deregulating metabolic and proteostatic pathways. In particular, foxo overexpression counteracts the proteostatic pathways in an Nrf2/cncC dependent-manner, ameliorating the aberrant foxo overexpression-mediated toxicity [108].…”

Sustained Nrf2 Overexpression-Induced Metabolic Deregulation Can Be Attenuated by Modulating Insulin/Insulin-like Growth Factor Signaling

“…For measuring proteasome peptidase activity, 10 dissected flies' tissues (equal number of males and females) were lysed on ice in a buffer suitable for isolation of intact 26S proteasomes (0.2% NP-40, 5 mM ATP (fresh), 10% glycerol, 20 mM KCl, 1 mM EDTA, 1 mM DDT, and 20 mM Tris, pH 7.6). Protein content was adjusted with Bradford (Bio-Rad, Hercules CA, USA) and cleared supernatants were immediately used to determine the chymotrypsin-like (CT-L/LLVY) or caspase-like (C-L/LLE) proteasome proteolytic activities after recording (excitation, 350 nm; emission, 440 nm) the hydrolysis of the fluorogenic peptides Suc-Leu-Leu-Val-Tyr-AMC and Z-Leu-Leu-Glu-AMC, (Enzo Life Sciences, Farmingdale, NY, USA), respectively, at 37 • C for 30 min [24,25]. Equal numbers of male and female flies were used.…”

ROS: Basic Concepts, Sources, Cellular Signaling, and its Implications in Aging Pathways

“…Furthermore, FOXO proteins promote numerous downstream target genes encoding antioxidant enzymes that regulate redox homeostasis, including superoxide dismutase Oxidative Medicine and Cellular Longevity (SOD) and catalase, in an NAD + -dependent manner [170]. In addition, genetic variants of FOXO3 are associated with longevity in worms, flies, and mammals, and protective alleles of FOXO3 are the second most replicated genetic factors related to prolonged human life, with findings of about 40 unique nucleotide polymorphisms (SNPs) noncoding consistently associated with longevity in humans [171].…”