Genes Related to Fatty Acid β-Oxidation Play a Role in the Functional Decline of the Drosophila Brain with Age

Fatty acid β-oxidation in brain mitochondria: Insights from high-resolution respirometry in mouse, rat and Drosophila brain, ischemia and aging models

Glucose is the main energy source of the brain, yet recent studies demonstrate that fatty acid oxidation (FAO) plays a relevant role in the pathogenesis of central nervous system disorders. We evaluated FAO in brain mitochondria under physiological conditions, in the aging brain, and after stroke. Using high-resolution respirometry we compared medium-chain (MC, octanoylcarnitine) and long-chain (LC, palmitoylcarnitine) acylcarnitines as substrates of β-oxidation in the brain. The protocols developed avoid FAO overestimation by malate-linked anaplerotic activity in brain mitochondria. The capacity of FA oxidative phosphorylation (F-OXPHOS) with palmitoylcarnitine was up to 4 times higher than respiration with octanoylcarnitine. The optimal concentration of palmitoylcarnitine was 10 μM which corresponds to the total concentration of LC acylcarnitines in the brain. Maximal respiration with octanoylcarnitine was reached at 20 μM, however, this concentration exceeds MC acylcarnitine concentrations in the brain 15 times. F-OXPHOS capacity was highest in mouse cerebellum, intermediate in cortex, prefrontal cortex, and hypothalamus, and hardly detectable in hippocampus. F-OXPHOS capacity was 2-fold lower and concentrations of LC acylcarnitines were 2-fold higher in brain of aged rats. A similar trend was observed in the rat model of endothelin-1-induced stroke, but reduction of OXPHOS capacity was not limited to FAO. In conclusion, although FAO is not a dominant pathway in brain bioenergetics, it deserves specific attention in studies of brain metabolism.

The Role of Acyl-CoA β-Oxidation in Brain Metabolism and Neurodegenerative Diseases

This review highlights the complex role of fatty acid β-oxidation in brain metabolism. It demonstrates the fundamental importance of fatty acid degradation as a fuel in energy balance and as an essential component in lipid homeostasis, brain aging, and neurodegenerative disorders.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte Nuclear Factor 4

Sexual attraction and perception are crucial for mating and reproductive success. In Drosophila melanogaster, the male-specific isoform of Fruitless (Fru), FruM, is a known master neuro-regulator of innate courtship behavior to control the perception of sex pheromones in sensory neurons. Here, we show that the non-sex-specific Fru isoform (FruCOM) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of FruCOM in oenocytes resulted in adults with reduced levels of cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 (Hnf4) as a key target of FruCOM in directing fatty acid conversion to hydrocarbons. Fru or Hnf4 depletion in oenocytes disrupts lipid homeostasis, resulting in a sex-dimorphic CHC profile that differs from doublesex- and transformer-dependent CHC dimorphism. Thus, Fru couples pheromone perception and production in separate organs to regulate chemosensory communications and ensure efficient mating behavior.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte nuclear factor 4

Sexual attraction and perception, governed by separate genetic circuits in different organs, are crucial for mating and reproductive success, yet the mechanisms of how these two aspects are integrated remain unclear. In Drosophila , the male-specific isoform of Fruitless (Fru), Fru M , is known as a master neuro-regulator of innate courtship behavior to control perception of sex pheromones in sensory neurons. Here we show that the non-sex specific Fru isoform (Fru COM ) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of Fru COM in oenocytes resulted in adults with reduced levels of the cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 ( Hnf4 ) as a key target of Fru COM in directing fatty acid conversion to hydrocarbons in adult oenocytes. fru - and Hnf4 -depletion disrupts lipid homeostasis, resulting in a novel sex-dimorphic CHC profile, which differs from doublesex - and transformer -dependent sexual dimorphism of the CHC profile. Thus, Fru couples pheromone perception and production in separate organs for precise coordination of chemosensory communication that ensures efficient mating behavior.

Teaser

Fruitless and lipid metabolism regulator HNF4 integrate pheromone biosynthesis and perception to ensure robust courtship behavior.

The Reversible Carnitine Palmitoyltransferase 1 Inhibitor (Teglicar) Ameliorates the Neurodegenerative Phenotype in a Drosophila Huntington’s Disease Model by Acting on the Expression of Carnitine-Related Genes

Huntington’s disease (HD) is a dramatic neurodegenerative disorder caused by the abnormal expansion of a CAG triplet in the huntingtin gene, producing an abnormal protein. As it leads to the death of neurons in the cerebral cortex, the patients primarily present with neurological symptoms, but recently metabolic changes resulting from mitochondrial dysfunction have been identified as novel pathological features. The carnitine shuttle is a complex consisting of three enzymes whose function is to transport the long-chain fatty acids into the mitochondria. Here, its pharmacological modification was used to test the hypothesis that shifting metabolism to lipid oxidation exacerbates the HD symptoms. Behavioural and transcriptional analyses were carried out on HD Drosophila model, to evaluate the involvement of the carnitine cycle in this pathogenesis. Pharmacological inhibition of CPT1, the rate-limiting enzyme of the carnitine cycle, ameliorates the HD symptoms in Drosophila, likely acting on the expression of carnitine-related genes.

Gene expression and alternative splicing dynamics are perturbed in female head transcriptomes following heterospecific copulation

BACKGROUND

Despite the growing interest in the female side of copulatory interactions, the roles played by differential expression and alternative splicing mechanisms of pre-RNA on tissues outside of the reproductive tract have remained largely unknown. Here we addressed these questions in the context of con- vs heterospecific matings between Drosophila mojavensis and its sister species, D. arizonae. We analyzed transcriptional responses in female heads using an integrated investigation of genome-wide patterns of gene expression, including differential expression (DE), alternative splicing (AS) and intron retention (IR).

RESULTS

Our results indicated that early transcriptional responses were largely congruent between con- and heterospecific matings but are substantially perturbed over time. Conspecific matings induced functional pathways related to amino acid balance previously associated with the brain's physiology and female postmating behavior. Heterospecific matings often failed to activate regulation of some of these genes and induced expression of additional genes when compared with those of conspecifically-mated females. These mechanisms showed functional specializations with DE genes mostly linked to pathways of proteolysis and nutrient homeostasis, while AS genes were more related to photoreception and muscle assembly pathways. IR seems to play a more general role in DE regulation during the female postmating response.

CONCLUSIONS

We provide evidence showing that AS genes substantially perturbed by heterospecific matings in female heads evolve at slower evolutionary rates than the genome background. However, DE genes evolve at evolutionary rates similar, or even higher, than those of male reproductive genes, which highlights their potential role in sexual selection and the evolution of reproductive barriers.

L-Carnitine in Drosophila: A Review

L-Carnitine is an amino acid derivative that plays a key role in the metabolism of fatty acids, including the shuttling of long-chain fatty acyl CoA to fuel mitochondrial β-oxidation. In addition, L-carnitine reduces oxidative damage and plays an essential role in the maintenance of cellular energy homeostasis. L-carnitine also plays an essential role in the control of cerebral functions, and the aberrant regulation of genes involved in carnitine biosynthesis and mitochondrial carnitine transport in Drosophila models has been linked to neurodegeneration. Drosophila models of neurodegenerative diseases provide a powerful platform to both unravel the molecular pathways that contribute to neurodegeneration and identify potential therapeutic targets. Drosophila can biosynthesize L-carnitine, and its carnitine transport system is similar to the human transport system; moreover, evidence from a defective Drosophila mutant for one of the carnitine shuttle genes supports the hypothesis of the occurrence of β-oxidation in glial cells. Hence, Drosophila models could advance the understanding of the links between L-carnitine and the development of neurodegenerative disorders. This review summarizes the current knowledge on L-carnitine in Drosophila and discusses the role of the L-carnitine pathway in fly models of neurodegeneration.

Effect of Aging on Daily Rhythms of Lactate Metabolism in the Medial Prefrontal Cortex of Male Mice

Aging is associated with reduced amplitude and earlier timing of circadian (daily) rhythms in sleep, brain function, and behavior. We examined whether age-related circadian dysfunction extends to the metabolic function of the brain, particularly in the prefrontal cortex (PFC). Using enzymatic amperometric biosensors, we recorded lactate concentration changes in the PFC in Young (7 mos) and Aged (19 mos) freely-behaving C57BL/6N male mice. Both Young and Aged mice displayed diurnal and circadian rhythms of lactate, with the Aged rhythm slightly phase advanced. Under constant conditions, the Aged rhythm showed a reduced amplitude not seen in the Young mice. We simultaneously observed a relationship between arousal state and PFC lactate rhythm via electroencephalography, which was modified by aging. Finally, using RT-qPCR, we found that aging affects the daily expression pattern of Glucose Transporter 1 (GLUT-1).

Astrocyte activation and altered metabolism in normal aging, age-related CNS diseases, and HAND

Astrocytes regulate local cerebral blood flow, maintain ion and neurotransmitter homeostasis, provide metabolic support, regulate synaptic activity, and respond to brain injury, insults, and infection. Because of their abundance, extensive connectivity, and multiple roles in the brain, astrocytes are intimately involved in normal functioning of the CNS and their dysregulation can lead to neuronal dysfunction. In normal aging, decreased biological functioning and reduced cognitive abilities are commonly experienced in individuals free of overt neurological disease. Moreover, in several age-related CNS diseases, chronic inflammation and altered metabolism have been reported. Since people with HIV (PWH) are reported to experience rapid aging with chronic inflammation, altered brain metabolism is likely to be exacerbated. In fact, many studies report altered metabolism in astrocytes in diseases such as Alzheimer's, Parkinson's, and HIV. This review will address the roles of astrocyte activation and altered metabolism in normal aging, in age-related CNS disease, and in HIV-associated neurocognitive disorders.

Cerebral Metabolic Changes During Sleep

PURPOSE OF REVIEW

The goal of the present paper is to review current literature supporting the occurrence of fundamental changes in brain energy metabolism during the transition from wakefulness to sleep.

RECENT FINDINGS

Latest research in the field indicates that glucose utilization and the concentrations of several brain metabolites consistently change across the sleep-wake cycle. Lactate, a product of glycolysis that is involved in synaptic plasticity, has emerged as a good biomarker of brain state. Sleep-induced changes in cerebral metabolite levels result from a shift in oxidative metabolism, which alters the reliance of brain metabolism upon carbohydrates. We found wide support for the notion that brain energetics is state dependent. In particular, fatty acids and ketone bodies partly replace glucose as cerebral energy source during sleep. This mechanism plausibly accounts for increases in biosynthetic pathways and functional alterations in neuronal activity associated with sleep. A better account of brain energy metabolism during sleep might help elucidate the long mysterious restorative effects of sleep for the whole organism.