Biology subjects

Alexaki, V. I.

Publications and source records attributed to Alexaki, V. I..

7 recordsLinked to original sources

bioRxiv2025

ACOD1 regulates microglial arginine metabolism and inflammatory responses

Itaconate is produced by inflammatory macrophages and promotes a negative feedback on inflammation. It is synthesized by aconitate decarboxylase 1 (ACOD1) from cis- aconitate, a metabolite of the tricarboxylic acid cycle. Here, we studied the role of ACOD1 in the inflammatory response of microglia, the resident macrophage-like cells of the brain. Similar to macrophages, ACOD1 deficient microglia displayed a stronger inflammatory response to lipopolysaccharide (LPS) compared to their wild type counterparts. The proinflammatory effects of ACOD1 deficiency were associated with reprogramed arginine metabolism entailing enhanced argininosuccinate synthesis at the expense of polyamine synthesis, in a manner that was dependent on ACLY. These findings provide new insights in the immunometabolic role of ACOD1 in inflammatory microglia.

immunology↗

bioRxiv2025

Functional Dichotomy of Developmental Foxp3+ Treg Cell Subsets in the Visceral Adipose Tissue of Lean and Obese Mice

Chronic inflammation and loss of Foxp3+ regulatory T (Treg) cells in the visceral adipose tissue (VAT) are hallmarks of the pathogenesis of insulin resistance and obesity. This study explores the roles of VAT Treg cells from thymic (tTreg) and peripheral (pTreg) developmental origin, revealing their opposing roles in metabolic inflammation. Obesity destabilized VAT tTreg cells, causing them to clonally expand into obesogenic Foxp3-IFN-{gamma}+ T effector cells, enhancing pro-inflammatory type 1 responses. Genetic tTreg ablation prevented this shift, promoting anti-inflammatory type 2 response, reduced body weight, and improved insulin resistance. Compared to their tTreg counterpart, pTreg cells were functionally well adapted to maintain VAT homeostasis and protect against obesity. Genetic pTreg ablation promoted spontaneous obesity symptoms even with physiological calorie intake, and worsened VAT inflammation and liver steatosis on a high-calorie diet. These findings highlight tTreg instability as a pathogenic threat and pTreg cells as crucial regulators of metabolic homeostasis. HighlightsO_LIVAT Tregs of lean mice originate from both thymic and peripheral Treg development C_LIO_LIHigh-calorie diet destabilizes tTregs that clonally expand into obesogenic IFN-{gamma}+ Th1 cells C_LIO_LIGenetic tTreg deficiency improves steady-state metabolism and prevents diet-induced obesity C_LIO_LIGenetic pTreg deficiency promotes obesity in both sexes even with normal calorie intake C_LIO_LIVAT pTregs are particularly adapted to regulate VAT homeostasis, including adipogenesis C_LI In BriefObesity and type 2 diabetes are characterized by insulin resistance, regulatory T (Treg) cell loss, and chronic inflammation in visceral adipose tissue (VAT). In this context, Yilmazer et al. dissect the functional roles of tTreg and pTreg cells. They show that VAT pTreg cells are particularly adapted to exert non-redundant homeostatic functions, and that pTreg deficiency predisposes to obesity even with normal calorie intake. In contrast, VAT tTreg cells can contribute to local inflammation by dedifferentiating into Foxp3- Th1-polarized effector cells. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/642664v1_ufig1.gif" ALT="Figure 1"> View larger version (60K): org.highwire.dtl.DTLVardef@19c740corg.highwire.dtl.DTLVardef@86d52borg.highwire.dtl.DTLVardef@152a88org.highwire.dtl.DTLVardef@19b7b13_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2024

AZIN2-dependent polyamine metabolism determines adipocyte progenitor fate and protects against obesity and dysmetabolism

Adipose tissue homeostasis plays a critical role in metabolic disease but the metabolic circuitry regulating adipose tissue dynamics remains unclear. In this study, polyamine metabolism emerges as an important regulator of adipose tissue pathophysiology. We identify AZIN2 (Antizyme inhibitor 2), a protein promoting polyamine synthesis and acetylation, as a major regulator of total acetyl-CoA in adipocyte progenitors (APs). AZIN2 deficient APs demonstrate increased H3K27 acetylation marks in genes related to lipid metabolism, cell cycle arrest and cellular senescence, and enhanced adipogenesis compared to wild-type counterparts. Upon high-fat diet (HFD)-induced obesity, global AZIN2 deficiency in mice provokes adipose tissue hypertrophy, AP senescence, lipid storage perturbations, inflammation and insulin resistance. IL4 promotes Azin2 expression in APs but not mature adipocytes due to diminished IL4 receptor expression in the latter. In human visceral and subcutaneous adipose tissue, AZIN2 expression positively correlates with expression of early progenitor markers and genes associated with protection against insulin resistance, while it negatively correlates with markers of lipogenesis. In sum, AZIN2-driven polyamine metabolism preserves adipose tissue health, a finding that could be therapeutically harnessed for the management of obesity-associated metabolic disease.

cell biology↗

bioRxiv2024

HIF1α controls steroidogenesis under acute hypoxic stress

BackgroundHypoxia is a critical physiological and pathological condition known to influence various cellular processes, including steroidogenesis. While previous studies, including our own, have highlighted the regulatory effects of Hypoxia-Inducible Factor 1 (HIF1) on steroid production, the specific molecular mechanisms remain poorly understood. This study investigates the role of hypoxia and HIF1 in steroid biosynthesis across multiple experimental models during acute exposure to low oxygen levels. MethodsTo assess the extent to which acute hypoxia modulates steroidogenesis, we employed several approaches, including the Y1 adrenocortical cell line, an ex vivo adrenal gland explant model, and a conditional HIF1-deficient mouse line in the adrenal cortex. We focused on various regulatory patterns that may critically suppress steroidogenesis. ResultsIn Y1 cells and adrenal gland explants, hypoxia induced the upregulation of specific microRNAs, leading to the suppression of mRNA levels of key steroidogenic enzymes and reduced steroid hormone production. The hypoxia/HIF1-dependent induction of these microRNAs and the consequent modulation of steroid production were confirmed in vivo. Notably, using our conditional HIF1-deficient mouse line, we found that the increase in miRNA expression under hypoxic conditions is directly dependent on HIF1. Furthermore, the regulation of steroidogenic enzymes (e.g., StAR and Cyp11a1) and steroid production occurred at the level of protein translation, revealing an unexpected layer of control under hypoxic conditions in vivo. ConclusionsThese findings elucidate the molecular mechanisms underlying acute hypoxia-induced changes in steroid biosynthesis and may also be useful in developing new strategies for various steroid hormone pathologies.

molecular biology↗

bioRxiv2022

INFLAMMATION INDUCED DOWNREGULATION OF SUCCINATE DEHYDROGENASE REGULATES ADRENOCORTICAL FUNCTION

The hypothalamus-pituitary-adrenal (HPA) axis is activated in response to inflammation leading to increased production of anti-inflammatory glucocorticoids by the adrenal cortex, thereby representing an endogenous feedback loop. However, severe inflammation reduces the responsiveness of the adrenal gland to adrenocorticotropic hormone (ACTH) although the underlying mechanisms are poorly understood. Here, we show by transcriptomic, proteomic and metabolomic analyses that LPS-induced systemic inflammation triggers profound metabolic changes in steroidogenic adrenocortical cells, including downregulation of the TCA cycle and oxidative phosphorylation. Inflammation disrupts the TCA cycle at the level of succinate dehydrogenase (SDH) leading to succinate accumulation and disturbed steroidogenesis. Mechanistically, IL-1{beta} reduces SDHB expression through upregulation of DNA methyltransferase 1 (DNMT1) and methylation of the SDHB promoter. Consequently, increased succinate levels impair oxidative phosphorylation and ATP synthesis, leading to reduced steroidogenesis. Together, we demonstrate that the IL-1{beta}-DNMT1-SDHB-succinate axis disrupts steroidogenesis. Our findings not only provide a mechanistic explanation for the adrenal dysfunction in severe inflammation but also a potential target for therapeutic intervention.

immunology↗

bioRxiv2020

Obesity-associated lipidomic remodeling of the adrenal gland indicates an important role of the FADS2-arachidonic acid axis in adrenocortical hormone production

ObjectiveAdrenocortical hormone levels increase in obesity, potentially contributing to development of obesity-associated pathologies. Here we explored whether lipidomic remodeling of the adrenal gland could mediate altered adrenocortical steroidogenesis during obesity. MethodsLipidomic analysis was performed in adrenal glands using shotgun mass spectrometry (MS), and steroid profiling of sera by liquid chromatography tandem mass spectrometry (LC-MS/MS) from lean and obese mice. Gene expression analysis was performed in adrenal glands and adrenocortical cell populations. The role of Fatty Acid Desaturase 2 (FADS2) and arachidonic acid on steroid hormone production was studied in primary adrenal gland cell cultures. ResultsAdrenal glands of obese mice displayed a distinct lipidomic profile, encompassing longer and more unsaturated storage lipids and phospholipids compared to adrenal glands of lean mice. Arachidonoyl acyl chains were abundant in the adrenal gland phospholipidome and increased upon obesity. This was accompanied by increased Fads2 expression, the rate-limiting enzyme of arachidonic acid synthesis, and enhanced plasma adrenocortical hormone levels. Inhibition of FADS2 in primary adrenal gland cell cultures abolished steroidogenesis, which was restored by arachidonic acid supplementation. ConclusionsOur data suggest that the FADS2 - arachidonic acid axis regulates adrenocortical hormone synthesis, while alterations in the content of arachidonoyl chains in the adrenal gland phopsholipidome could account for disturbed adrenocortical hormone production. HighlightsO_LIThe adrenal gland lipidome is remodeled in obesity. C_LIO_LIArachidonoyl groups are abundant in the adrenal gland phospholipidome and increase in obesity. C_LIO_LIFADS2 is highly expressed in the adrenal gland and its expression is further increased in obesity. C_LIO_LIFADS2 inhibition blunts adrenocortical steroidogenesis in primary adrenal gland cell cultures, while arachidonic acid supplementation restores it. C_LI

cell biology↗

bioRxiv2018

Comprehensive and quantitative analysis of white and brown adipose tissue by shotgun lipidomics

Shotgun lipidomics enables an extensive analysis of lipids from tissues and fluids. Each specimen requires appropriate extraction and processing procedures to ensure good coverage and reproducible quantification of the lipidome. Adipose tissue (AT) has become a research focus with regard to its involvement in obesity-related pathologies. However, the quantification of the AT lipidome is particularly challenging due to the predominance of triacylglycerides, which elicit high ion suppression of the remaining lipid classes. We present a new and validated method for shotgun lipidomics of AT, which tailors the lipid extraction procedure to the target specimen and features high reproducibility with a linear dynamic range of at least 4 orders of magnitude for all lipid classes. Utilizing this method, we observed tissue-specific and diet-related differences in three AT types (brown, gonadal, inguinal subcutaneous) from lean and obese mice. Brown AT exhibited a distinct lipidomic profile with the greatest lipid class diversity and responded to high-fat diet by altering its lipid composition, which shifted towards that of white AT. Moreover, diet-induced obesity promoted an overall remodelling of the lipidome, where all three AT types featured a significant increase in longer and more unsaturated triacylglyceride and phospholipid species.\n\nThe here presented method facilitates reproducible systematic lipidomic profiling of AT and could be integrated with further -omics approaches used in (pre-)clinical research, in order to advance the understanding of the molecular metabolic dynamics involved in the pathogenesis of obesity-associated disorders.

physiology↗