Biology subjects

Garcia, T. Y.

Publications and source records attributed to Garcia, T. Y..

5 recordsLinked to original sources

bioRxiv2026

Requirement for oxidation of neuronal ketone bodies in aging andneurodegeneration

Glucose is the brains primary fuel, but the brain can also use alternative energy substrates, especially during development or starvation. Emerging evidence suggests ketone metabolism may help the brain adapt to energy stress in neurodegenerative diseases such as Alzheimers disease, although its role in constitutive brain function in normal aging is poorly understood. Using iPSC-derived human neurons and adult-inducible, neuron-specific Bdh1 knockout mice, we show that ketone body metabolism is essential for maximum energy production, neuronal function, and mouse survival--even under normal nutritional conditions. Mechanistically, phenotypes of Bdh1 knockout neurons are mitigated by provision of acetoacetate, a downstream energy metabolite. Moreover, loss of neuronal ketone oxidation markedly increases mortality and memory deficits in Alzheimers disease model mice. These findings identify ketones as critical neuronal fuels, with particular importance during neurodegeneration. While non-energetic activities of ketone bodies are increasingly appreciated, oxidation for energy provision is an essential mechanism for normal function in neurons and mice. Targeting the energetic function of ketones may thus offer new therapeutic strategies for both aging and neurodegenerative diseases such as Alzheimers.

neuroscience↗

bioRxiv2023

A ketogenic diet reduces age-induced chronic neuroinflammation in mice

Beta-hydroxybutyrate (BHB) is a ketone body synthesized during fasting or strenuous exercise. Our previous study demonstrated that a cyclic ketogenic diet (KD), which induces BHB levels similar to fasting every other week, reduces midlife mortality and improves memory in aging mice. BHB actively regulates gene expression and inflammatory activation through non-energetic signaling pathways. Neither of these activities has been well-characterized in the brain and they may represent mechanisms by which BHB affects brain function during aging. First, we analyzed hepatic gene expression in an aging KD-treated mouse cohort using bulk RNA-seq. In addition to the downregulation of TOR pathway activity, cyclic KD reduces inflammatory gene expression in the liver. We observed via flow cytometry that KD also modulates age-related systemic T cell functions. Next, we investigated whether BHB affects brain cells transcriptionally in vitro. Gene expression analysis in primary human brain cells (microglia, astrocytes, neurons) using RNA-seq shows that BHB causes a mild level of inflammation in all three cell types. However, BHB inhibits the more pronounced LPS-induced inflammatory gene activation in microglia. Furthermore, we confirmed that BHB similarly reduces LPS-induced inflammation in primary mouse microglia and bone marrow-derived macrophages (BMDMs). BHB is recognized as an inhibitor of histone deacetylase (HDAC), an inhibitor of NLRP3 inflammasome, and an agonist of the GPCR Hcar2. Nevertheless, in microglia, BHBs anti-inflammatory effects are independent of these known mechanisms. Finally, we examined the brain gene expression of 12-month-old male mice fed with one-week and one-year cyclic KD. While a one-week KD increases inflammatory signaling, a one-year cyclic KD reduces neuroinflammation induced by aging. In summary, our findings demon-strate that BHB mitigates the microglial response to inflammatory stimuli, like LPS, possibly leading to decreased chronic inflammation in the brain after long-term KD treatment in aging mice.

immunology↗

bioRxiv2023

β-hydroxybutyrate is a metabolic regulator of proteostasis in the aged and Alzheimer disease brain

Loss of proteostasis is a hallmark of aging and Alzheimer disease (AD). Here, we identify {beta}-hydroxybutyrate ({beta}HB), a ketone body, as a regulator of protein solubility in the aging brain. {beta}HB is a small molecule metabolite which primarily provides an oxidative substrate for ATP during hypoglycemic conditions, and also regulates other cellular processes through covalent and noncovalent protein interactions. We demonstrate {beta}HB-induced protein insolubility across in vitro, ex vivo, and in vivo mouse systems. This activity is shared by select structurally similar metabolites, is not dependent on covalent protein modification, pH, or solute load, and is observable in mouse brain in vivo after delivery of a ketone ester. Furthermore, this phenotype is selective for pathological proteins such as amyloid-{beta}, and exogenous {beta}HB ameliorates pathology in nematode models of amyloid-{beta} aggregation toxicity. We have generated a comprehensive atlas of the {beta}HB-induced protein insolublome ex vivo and in vivo using mass spectrometry proteomics, and have identified common protein domains within {beta}HB target sequences. Finally, we show enrichment of neurodegeneration-related proteins among {beta}HB targets and the clearance of these targets from mouse brain, likely via {beta}HB-induced autophagy. Overall, these data indicate a new metabolically regulated mechanism of proteostasis relevant to aging and AD.

physiology↗

bioRxiv2022

Ketone body metabolism declines with age in mice in a sex-dependent manner

Understanding how our cells maintain energy homeostasis has long been a focus of aging biology. A decline in energy metabolism is central to many age-related diseases such as Alzheimers disease, heart failure, frailty, and delirium. Intervening on pathways involved in energy homeostasis can extend healthy lifespan. When the primary energy substrate glucose is scarce, mice and humans can partially switch cellular energetic needs to fat-derived ketone bodies (i.e., beta-hydroxybutyrate (BHB), acetoacetate, acetone). Aging is associated with glucose intolerance and insulin insensitivity, yet, surprisingly, what role ketone body metabolism might play in compensating for impaired glucose utilization in age-related diseases is understudied. Here, we investigate how endogenous ketone body production and utilization pathways are modulated by age across the lifespan of male and female C57BL/6N mice (3 mo old, 12 mo old, 22 mo old). We show how different ages have different metabolic and gene expression responses to 1-week ketogenic diet (KD). We hypothesized that there would be a compensatory ketogenic response with age but instead saw declines in plasma BHB concentrations under fasting and non-fasting conditions with strong sexual dimorphism. Under KD, both sexes increased BHB concentrations at all ages, but only males showed strong gene expression induction. We also observed tissue-specific changes with age in baseline ketone metabolism, and surprising induction of extrahepatic ketogenic genes under KD. We found significant residual blood concentrations of BHB in KD even after a knockout of liver BHB production. Overall, these findings show that older mice have impaired non-fasting ketogenesis but are capable of increasing their ketogenic capacity under stimulation (i.e., KD) to meet energetic demands in aging. Therapies to augment non-fasting ketogenesis or provide exogenous ketones may be useful to improve energy homeostasis in diseases and conditions of aging.

physiology↗

bioRxiv2019

Proteome and Secretome Dynamics of Stem Cell-Derived Retinal Pigmented Epithelium in Response to Acute and Chronic ROS

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries, and is characterized by slow retinal degeneration linked to chronic oxidative stress in the retinal pigmented epithelium (RPE). The exact molecular mechanisms that lead to RPE death and dysfunction in response to chronic reactive oxygen species (ROS) are still unclear. In this work, human stem cell-derived RPE samples were treated with a low dose of paraquat (PQ) for 1 week or 3 weeks to induce chronic reactive oxygen species (ROS) stress. Cells were then harvested and both the intracellular and secreted RPE proteomes were quantified by mass spectrometry. Inside the RPE, chronic ROS caused concerted increase of glycolytic proteins but decreased mitochondrial proteins, as well as decreased extracellular matrix proteins and membrane proteins required for endocytosis. From the secreted proteins, we found that stressed RPE secrete over 1,000 detectable proteins, and the composition of the proteins secreted from RPE changes due to chronic ROS. Notably, secreted APOE is decreased 4-fold due to 3 weeks of chronic ROS stress, and urotensin-II, the strongest known vasoconstrictor, doubles. Further, secreted TGF-beta is increased, and its cognate signaler BMP1 decreased in the secretome. Together, these alterations of the RPE proteome and protein secretome paint a detailed molecular picture of the retinal stress response in space and time.

systems biology↗