Adipocyte metabolic state regulates glial phagocytic function

Abstract

Excess dietary sugar profoundly impacts organismal metabolism and health, yet it remains unclear how metabolic adaptations in adipose tissue influence other organs, including the brain. Here, we show that a high-sugar diet (HSD) in Drosophila reduces adipocyte glycolysis and mitochondrial pyruvate uptake, shifting metabolism toward fatty acid oxidation and ketogenesis. These metabolic changes trigger mitochondrial oxidation and elevate antioxidant responses. Adipocyte-specific manipulations of glycolysis, lipid metabolism, or mitochondrial dynamics non-autonomously modulate Draper expression in brain ensheathing glia, key cells responsible for neuronal debris clearance. Adipocyte-derived ApoB-containing lipoproteins maintain basal Draper levels in glia via LpR1, critical for effective glial phagocytic activity. Accordingly, reducing ApoB or LpR1 impairs glial clearance of degenerating neuronal debris after injury. Collectively, our findings demonstrate that dietary sugar-induced shifts in adipocyte metabolism substantially influence brain health by modulating glial phagocytosis, identifying adipocyte-derived ApoB lipoproteins as essential systemic mediators linking metabolic state with neuroprotective functions.

Keywords: ApoB; CP: Metabolism; CP: Neuroscience; Drosophila; OxPhos; adipokine; glycolysis; high-sugar diet; injury-response; ketogenesis; lipid metabolism; mitochondria; neurodegeneration; pyronic sensor.

Figure 1.. An HSD induces a metabolic shift in fly adipose tissue

(A) Schematic of glycolysis pathway enzymes (HexA, PyK, and Ldh). (B and K) Fold change (qPCR) of the indicated mRNA relative to α-tubulin in the adipose tissue of flies fed either an ND or an HSD for 3 weeks. Student’s t test with Welch’s correction. N = 3 technical replicates of cDNA collected from 30 fly abdominal segments/treatment. (C and D) Confocal images (C) and quantification (D) of adipocyte Ldh-GFP intensity. Scale bar: 10 μm. Student’s t test (Welch’s). Each dot represents an individual fly. (E) Schematic: mitochondrial fission-fusion balance. (F) TEM images of adipocyte mitochondria (white outline), ND vs. HSD at 1 week. Scale bar: 1 μm. (G–I) Confocal mito-GFP images (G), mitochondrial circularity (H), and elongation (I). Scale bar: 10 μm (top) and 5 μm (bottom). Student’s t test; dots represent individual flies. (J) Mitochondrial pyruvate uptake. (L and L′) Confocal live imaging (L) and quantification (L′) of mitochondrial pyruvate uptake (mitoPyronicSF) at baseline and pyruvate addition (5 and 10 mM). Scale bar: 10 μm. Student’s t test. All experiments except (F): 3 weeks of diet (ND or HSD). Statistical significance was determined using Student’s t test (with Welch’s correction where appropriate). Exact p values are indicated; all error bars represent ±SD. See also Figure S1.

Figure 2.. Molecular characterization of metabolic changes in the adipose tissue

(A) Schematic: metabolic shift toward FA oxidation (FAO) induced by an HSD. (B and C) Confocal images (B) and quantification (C) of adipocyte Plin1 intensity in w1118 fat bodies; ND vs. HSD. Scale bar: 20 μm. Student’s t test (Welch’s). Each dot represents an individual fly. (D, E, and I) qPCR fold change of lipid metabolism (D), FAO enzyme genes (E), and antioxidant markers (I) in adult fat body explants; ND vs. HSD (3 weeks). Student’s t test (Welch’s) and one-way ANOVA; N = 3 replicates (each replicate contains 30 fat explants). (F and G) Metabolite quantification (μM): acetylcarnitine, α-HB, and β-HB, in whole flies, ND vs. HSD (2 weeks). Student’s t test (Welch’s); N = 3 replicates. 10 flies per replicate. (H and H′) Confocal images (H) and quantification (H′) of mitochondrial oxidation (MitoTimer) in adipocytes. Scale bar: 20 μm. Student’s t test (Welch’s); exact p values are indicated; dots represent individual flies; all error bars represent ±SD). See also Figure S2.

Figure 3.. Adipocyte lipid metabolism and mitochondrial dynamics regulate Draper in ensheathing glia

(A–C) Schematics illustrating the experimental context. (A) Adult fly brain schematic highlighting antennal lobes (ALs) and ensheathing glia. (A′) Representative confocal image showing Draper staining in ALs; the inset defines the analyzed region of interest (ROI) in (D)–(J). Scale bar: 20 μm. (B and C) Lipid metabolism and mitochondrial dynamics pathways, indicating adipocyte-specific genetic manipulations analyzed below. (D–J) Representative confocal z stack projections showing Draper staining in ALs ensheathing glia from flies with adipocyte-specific gene knockdown (bottom) vs. matched controls (top). Scale bar: 20 μm. (D′–J′) Quantification of Draper fluorescence intensity in ROIs (white boxes). Circles represent individual flies. Student’s t test with Welch’s correction; exact p values are shown; all error bars represent ±SD. See also Figure S3.

Figure 4.. Adipocyte-derived ApoB modulates baseline glial phagocytic competence and injury response

(A and A′) Western blot (A) and quantification (A′) of brain ApoII levels in control (w1118) flies after 3 weeks of ND or HSD. ApoII was normalized to tubulin; dots represent 10 pooled brains each (3–4 replicates). Student’s t test (Welch’s correction); exact p value is shown. (B and B′) Confocal images (B) and quantification (B′) of ApoB (purple) and Draper (cyan) co-localization (Manders’ coefficient) in ALs from control flies (w1118, ND vs. HSD). Insets show magnified merged and single-channel views. Dots represent single z-slices. Student’s t test (Welch’s); scale bars: 50 μm (top) and 20 μm (insets). (C–F) Confocal z stacks are shown and quantificatied. Basal (C and E) and injury-induced (D and F) Draper staining in antennal lobes after adipocyte ApoB-RNAi or glial LpR1-, LpR2-RNAi vs. controls (Luc-RNAi). (G–H′) Olfactory axon degeneration assay. (G and G′) Schematic of unilateral antennal ablation in ORN22-CD8GFP flies. (H and H′) Confocal z stacks (H) and quantification (H′) of GFP intensity in injured vs. uninjured axons after glial RNAi (Luc, LpR1, and LpR2), assessed 1 day post injury. Dots represent individual flies; Student’s t test (Welch’s); exact p values are shown; scale bar: 20 μm; all error bars represent ±SD. See also Figures S4–S6 and Tables S1 and S2.