Aging and Intermittent Fasting Impact on Transcriptional Regulation and Physiological Responses of Adult Drosophila Neuronal and Muscle Tissues.

The progressive decline of the nervous system, including protein aggregate formation, reflects the subtle dysregulation of multiple functional pathways. Our previous work has shown intermittent fasting (IF) enhances longevity, maintains adult behaviors and reduces aggregates, in part, by promoting autophagic function in the aging Drosophila brain. To clarify the impact that IF-treatment has upon aging, we used high throughput RNA-sequencing technology to examine the changing transcriptome in adult Drosophila tissues. Principle component analysis (PCA) and other analyses showed ~1200 age-related transcriptional differences in head and muscle tissues, with few genes having matching expression patterns. Pathway components showing age-dependent expression differences were involved with stress response, metabolic, neural and chromatin remodeling functions. Middle-aged tissues also showed a significant increase in transcriptional drift-variance (TD), which in the CNS included multiple proteolytic pathway components. Overall, IF-treatment had a demonstrably positive impact on aged transcriptomes, partly ameliorating both fold and variance changes. Consistent with these findings, aged IF-treated flies displayed more youthful metabolic, behavioral and basal proteolytic profiles that closely correlated with transcriptional alterations to key components. These results indicate that even modest dietary changes can have therapeutic consequences, slowing the progressive decline of multiple cellular systems, including proteostasis in the aging nervous system.

Bile acids decrease hepatic paraoxonase 1 expression and plasma high-density lipoprotein levels via FXR-mediated signaling of FGFR4.

OBJECTIVE: The purpose of this research was to determine how dietary bile acids repress hepatic expression of paraoxonase 1 (PON1). METHODS AND RESULTS: C57BL/6 mice and C3H/HeJ mice, having different susceptibilities to atherosclerosis, were fed a chow diet and an atherogenic diet containing taurocholate. Compared with the more atherosclerosis-susceptible C57BL/6 mice, C3H/HeJ mice display resistance to dietary bile acid repression of hepatic PON1 mRNA and decreased high-density lipoprotein cholesterol. Whereas knockout of toll receptor 4 did not affect response to taurocholate, deletion of either FXR or FGFR4 blocked taurocholate repression of PON1 and CYP7A1. FGF19, an activator of FGFR4 expressed in human ileum, decreased expression of both PON1 and CYP7A1 expression by human hepatoma cells. In all of the mice studied, dietary taurocholate increased ileal expression of FGF15, a FXR-inducible murine homologue of human FGF19. CONCLUSIONS: Hepatic PON1 and CYP7A1 mRNA expression is repressed by bile acids via FXR-mediated induction of FGF15. Thus, the inability of C3H/HeJ mice to display taurocholate repression of PON1 and CYP7A1 mRNAs was not because of a lack of induction of FGF15 but rather signaling events distal to FGF15-FGFR4 association.

Brain trauma and autophagy: What flies and mice can teach us about conserved responses.

Drosophila models have been successfully used to identify many genetic components that affect neurodegenerative disorders. Recently, there has been a growing interest in identifying innate and environmental factors that influence the individual outcomes following traumatic brain injury (TBI). This includes both severe TBI and more subtle, mild TBI (mTBI), which is common in people playing contact sports. Autophagy, as a clearance pathway, exerts protective effects in multiple neurological disease models. In a recent publication, we highlighted the development of a novel repetitive mTBI system using Drosophila, which recapitulates several phenotypes associated with trauma in mammalian models. In particular, flies subjected to mTBI exhibit an acute impairment of the macroautophagy/autophagy pathway that is restored 1 wk following traumatic injury exposure. These phenotypes closely resemble temporary autophagy defects observed in a mouse TBI model. Through these studies, we also identified methods to directly assess autophagic responses in the fly nervous system and laid the groundwork for future studies designed to identify genetic, epigenetic and environmental factors that have an impact on TBI outcomes.

Using Drosophila as an integrated model to study mild repetitive traumatic brain injury.

Traumatic brain injury (TBI) is a major cause of morbidity and mortality worldwide. In addition, there has been a growing appreciation that even repetitive, milder forms of TBI (mTBI) can have long-term deleterious consequences to neural tissues. Hampering our understanding of genetic and environmental factors that influence the cellular and molecular responses to injury has been the limited availability of effective genetic model systems that could be used to identify the key genes and pathways that modulate both the acute and long-term responses to TBI. Here we report the development of a severe and mild-repetitive TBI model using Drosophila. Using this system, key features that are typically found in mammalian TBI models were also identified in flies, including the activation of inflammatory and autophagy responses, increased Tau phosphorylation and neuronal defects that impair sleep-related behaviors. This novel injury paradigm demonstrates the utility of Drosophila as an effective tool to validate genetic and environmental factors that influence the whole animal response to trauma and to identify prospective therapies needed for the treatment of TBI.

Assessing Basal and Acute Autophagic Responses in the Adult Drosophila Nervous System: The Impact of Gender, Genetics and Diet on Endogenous Pathway Profiles.

The autophagy pathway is critical for the long-term homeostasis of cells and adult organisms and is often activated during periods of stress. Reduced pathway efficacy plays a central role in several progressive neurological disorders that are associated with the accumulation of cytotoxic peptides and protein aggregates. Previous studies have shown that genetic and transgenic alterations to the autophagy pathway impacts longevity and neural aggregate profiles of adult Drosophila. In this study, we have identified methods to measure the acute in vivo induction of the autophagy pathway in the adult fly CNS. Our findings indicate that the genotype, age, and gender of adult flies can influence pathway responses. Further, we demonstrate that middle-aged male flies exposed to intermittent fasting (IF) had improved neuronal autophagic profiles. IF-treated flies also had lower neural aggregate profiles, maintained more youthful behaviors and longer lifespans, when compared to ad libitum controls. In summary, we present methodology to detect dynamic in vivo changes that occur to the autophagic profiles in the adult Drosophila CNS and that a novel IF-treatment protocol improves pathway response in the aging nervous system.

Aging and Autophagic Function Influences the Progressive Decline of Adult Drosophila Behaviors.

Multiple neurological disorders are characterized by the abnormal accumulation of protein aggregates and the progressive impairment of complex behaviors. Our Drosophila studies demonstrate that middle-aged wild-type flies (WT, ~4-weeks) exhibit a marked accumulation of neural aggregates that is commensurate with the decline of the autophagy pathway. However, enhancing autophagy via neuronal over-expression of Atg8a (Atg8a-OE) reduces the age-dependent accumulation of aggregates. Here we assess basal locomotor activity profiles for single- and group-housed male and female WT flies and observed that only modest behavioral changes occurred by 4-weeks of age, with the noted exception of group-housed male flies. Male flies in same-sex social groups exhibit a progressive increase in nighttime activity. Infrared videos show aged group-housed males (4-weeks) are engaged in extensive bouts of courtship during periods of darkness, which is partly repressed during lighted conditions. Together, these nighttime courtship behaviors were nearly absent in young WT flies and aged Atg8a-OE flies. Previous studies have indicated a regulatory role for olfaction in male courtship partner choice. Coincidently, the mRNA expression profiles of several olfactory genes decline with age in WT flies; however, they are maintained in age-matched Atg8a-OE flies. Together, these results suggest that middle-aged male flies develop impairments in olfaction, which could contribute to the dysregulation of courtship behaviors during dark time periods. Combined, our results demonstrate that as Drosophila age, they develop early behavior defects that are coordinate with protein aggregate accumulation in the nervous system. In addition, the nighttime activity behavior is preserved when neuronal autophagy is maintained (Atg8a-OE flies). Thus, environmental or genetic factors that modify autophagic capacity could have a positive impact on neuronal aging and complex behaviors.

Mitophagy is required for acute cardioprotection by simvastatin.

AIMS: We have shown that autophagy and mitophagy are required for preconditioning. While statin's cardioprotective effects are well known, the role of autophagy/mitophagy in statin-mediated cardioprotection is not. In this study, we used HL-1 cardiomyocytes and mice subjected to ischemia/reperfusion to elucidate the mechanism of statin-mediated cardioprotection. RESULTS: HL-1 cardiomyocytes exposed to simvastatin for 24 h exhibited diminished protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling, increased activation of unc-51-like kinase 1, and upregulation of autophagy and mitophagy. Similar findings were obtained in hearts of mice given simvastatin. Mevalonate abolished simvastatin's effects on Akt/mTOR signaling and autophagy induction in HL-1 cells, indicating that the effects are mediated through inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Simvastatin-treated HL-1 cells exhibited mitochondrial translocation of Parkin and p62/SQSTM1, fission, and mitophagy. Because Parkin is required for mitophagy and is expressed in heart, we investigated the effect of simvastatin on infarct size in Parkin knockout mice. Simvastatin reduced infarct size in wild-type mice but showed no benefit in Parkin knockout mice. Inhibition of HMG-CoA reductase limits mevalonate availability for both cholesterol and coenzyme Q10 (CoQ) biosynthesis. CoQ supplementation had no effect on statin-induced Akt/mTOR dephosphorylation or macroautophagy in HL-1 cells, but it potently blocked mitophagy. Importantly, CoQ supplementation abolished statin-mediated cardioprotection in vivo. INNOVATION AND CONCLUSION: Acute simvastatin treatment suppresses mTOR signaling and triggers Parkin-dependent mitophagy, the latter which is required for cardioprotection. Coadministration of CoQ with simvastatin impairs mitophagy and cardioprotection. These results raise the concern that CoQ may interfere with anti-ischemic benefits of statins mediated through stimulation of mitophagy.

Diminished AMPK signaling response to fasting in thioredoxin-interacting protein knockout mice.

Thioredoxin-interacting protein (Txnip) knockout (TKO) mice exhibit impaired response to fasting. Herein, we showed that activation of adenine monophosphate-activated protein kinase and cellular AMP levels were diminished in the heart and soleus muscle but not in gastrocnemius muscle of fasting TKO mice. Similarly, glycogen content in fasted TKO mice was increased in oxidative muscles but was not different in glycolytic muscles. These data suggest Txnip deficiency has a higher impact on oxidative muscle than glycolytic muscles and provide new insights into the metabolic role of Txnip.

Preconditioning involves selective mitophagy mediated by Parkin and p62/SQSTM1.

Autophagy-dependent mitochondrial turnover in response to cellular stress is necessary for maintaining cellular homeostasis. However, the mechanisms that govern the selective targeting of damaged mitochondria are poorly understood. Parkin, an E3 ubiquitin ligase, has been shown to be essential for the selective clearance of damaged mitochondria. Parkin is expressed in the heart, yet its function has not been investigated in the context of cardioprotection. We previously reported that autophagy is required for cardioprotection by ischemic preconditioning (IPC). In the present study, we used simulated ischemia (sI) in vitro and IPC of hearts to investigate the role of Parkin in mediating cardioprotection ex vivo and in vivo. In HL-1 cells, sI induced Parkin translocation to mitochondria and mitochondrial elimination. IPC induced Parkin translocation to mitochondria in Langendorff-perfused rat hearts and in vivo in mice subjected to regional IPC. Mitochondrial depolarization with an uncoupling agent similarly induced Parkin translocation to mitochondria in cells and Langendorff-perfused rat hearts. Mitochondrial loss was blunted in Atg5-deficient cells, revealing the requirement for autophagy in mitochondrial elimination. Consistent with previous reports indicating a role for p62/SQSTM1 in mitophagy, we found that depletion of p62 attenuated mitophagy and exacerbated cell death in HL-1 cardiomyocytes subjected to sI. While wild type mice showed p62 translocation to mitochondria and an increase in ubiquitination, Parkin knockout mice exhibited attenuated IPC-induced p62 translocation to the mitochondria. Importantly, ablation of Parkin in mice abolished the cardioprotective effects of IPC. These results reveal for the first time the crucial role of Parkin and mitophagy in cardioprotection.

Transgenic expression of CYP7A1 in LDL receptor-deficient mice blocks diet-induced hypercholesterolemia.

Constitutive expression of a cholesterol-7alpha-hydroxylase (CYP7A1) transgene in LDL receptor-deficient mice blocked the ability of a cholesterol-enriched diet to increase plasma levels of apolipoprotein B-containing lipoproteins. LDL receptor-deficient mice expressing the CYP7A1 transgene exhibited complete resistance to diet-induced hypercholesterolemia and to the accumulation of cholesterol in the liver. Hepatic mRNA expression of liver X receptor-inducible ABCG5 and ABCG8 was decreased in CYP7A1 transgenic, LDL receptor-deficient mice fed a cholesterol-enriched diet. Thus, increased biliary cholesterol excretion could not account for the maintenance of cholesterol homeostasis. CYP7A1 transgenic, LDL receptor-deficient mice fed the cholesterol-enriched diet exhibited decreased jejunal Niemann-Pick C1-Like 1 protein (NPC1L1) mRNA expression, an important mediator of intestinal cholesterol absorption. A taurocholate-enriched diet also decreased NPC1L1 mRNA expression in a farnesoid X receptor-independent manner. Reduced expression of NPC1L1 mRNA was associated with decreased cholesterol absorption ( approximately 20%; P < 0.05) exhibited by CYP7A1 transgenic LDL receptor-deficient mice fed the cholesterol-enriched diet. The combined data show that enhanced expression of CYP7A1 is an effective means to prevent the accumulation of cholesterol in the liver and of atherogenic apolipoprotein B-containing lipoproteins in plasma.