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. 2021 Jun;28(6):1880-1899.
doi: 10.1038/s41418-020-00714-7. Epub 2021 Jan 18.

Kdm2a deficiency in macrophages enhances thermogenesis to protect mice against HFD-induced obesity by enhancing H3K36me2 at the Pparg locus

Affiliations

Kdm2a deficiency in macrophages enhances thermogenesis to protect mice against HFD-induced obesity by enhancing H3K36me2 at the Pparg locus

Longmin Chen et al. Cell Death Differ. 2021 Jun.

Abstract

Kdm2a catalyzes H3K36me2 demethylation to play an intriguing epigenetic regulatory role in cell proliferation, differentiation, and apoptosis. Herein we found that myeloid-specific knockout of Kdm2a (LysM-Cre-Kdm2af/f, Kdm2a-/-) promoted macrophage M2 program by reprograming metabolic homeostasis through enhancing fatty acid uptake and lipolysis. Kdm2a-/- increased H3K36me2 levels at the Pparg locus along with augmented chromatin accessibility and Stat6 recruitment, which rendered macrophages with preferential M2 polarization. Therefore, the Kdm2a-/- mice were highly protected from high-fat diet (HFD)-induced obesity, insulin resistance, and hepatic steatosis, and featured by the reduced accumulation of adipose tissue macrophages and repressed chronic inflammation following HFD challenge. Particularly, Kdm2a-/- macrophages provided a microenvironment in favor of thermogenesis. Upon HFD or cold challenge, the Kdm2a-/- mice manifested higher capacity for inducing adipose browning and beiging to promote energy expenditure. Collectively, our findings demonstrate the importance of Kdm2a-mediated H3K36 demethylation in orchestrating macrophage polarization, providing novel insight that targeting Kdm2a in macrophages could be a viable therapeutic approach against obesity and insulin resistance.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1. Obesity is featured by the reduced H3K36me2 levels in ATMs.
H3K36me2 levels in epWAT (A) and scWAT (B) of mice fed ND or HFD for 8 weeks (n = 4/group). Flow cytometry analysis of H3K36me2 status in CD45+ cells from epWAT (C) and scWAT (D) of mice fed with ND or HFD for 8 weeks. Left: a representative flow cytometry data; right: quantitative data from all mice analyzed (n = 5/group). Representative FACS plots showing the proportion of F4/80+ cells gated on CD45+ cells from epWAT (E) and scWAT (F) of mice fed with ND or HFD for 8 weeks. Representative FACS plots and quantitative data of H3K36me2 levels in macrophages from epWAT (G) and scWAT (H) of mice after 8 weeks of HFD or ND feeding (n = 5/group). I Western blot analysis of H3K36me2 levels in CD45+ cells isolated from scWAT of controls (n = 4) and obese subjects (n = 4). J Representative immunostaining results for CD68 and H3K36me2 in scWAT sections from controls and obese subjects. Scale bars: 50 μm. Original magnification: ×400. Values are expressed as mean ± SEM, and unpaired Student’s t test was employed for data analysis. *P < 0.05; **P < 0.01.
Fig. 2
Fig. 2. Kdm2a deficiency orchestrates alternative activation of macrophages.
A Strategy for generating a conditional Kdm2a-deficient model. Kdm2a exons 79 were flanked by a neo-flippase recognition target (FRT) and two loxP sites. The neo-gene was deleted after Flp recombination and the Kdm2a exons were then excised by Cre recombinase. B Western blot analysis of Kdm2a and H3K36me2 levels in BMDMs from WT and KO mice, and a bar graph showing data derived from three mice in each group. C Flow cytometry analysis of the expression of F4/80, CD11b, and CD11c in BMDMs stimulated with LPS for 24 h. The percentages of F4/80+CD11b+ and F4/80+CD11b+CD11c+ cells are shown. D RT-PCR analysis of relative mRNA expression of M1 marker genes in BMDMs stimulated with LPS for 6 h. E Flow cytometry analysis of the expression of F4/80, CD11b, and CD206 in BMDMs stimulated with IL-4 for 24 h. Percentages of F4/80+CD11b+CD206+ cells are shown in the bar graphic figure. F Western blot analysis of Arg1 expression in BMDMs stimulated with IL-4 with indicated time. G RT-PCR analysis of relative mRNA levels of M2 genes in BMDMs stimulated with IL-4 for 6 h. H Western blot analysis of Arg1 expression in peritoneal macrophages with or without IL-4 stimulation for 24 h. I RT-PCR analysis of relative mRNA levels of M2 genes in peritoneal macrophages stimulated with or without IL-4 for 6 h. J Representative FACS plots and the percentages of F4/80+CD11b+ cells in epWAT of ND-fed WT and KO mice at 16 weeks of age (n = 4/group). K Expression of CD206 in F4/80+CD11b+ cells as shown in (J). The amounts of F4/80+CD11b+CD206+ cells were quantified and shown as relative mean fluorescence intensity (MFI). Results are representative of three to four independent experiments (BI). Values are expressed as mean ± SEM, and unpaired Student’s t test was used for data analysis. *P < 0.05; **P < 0.01; ***P < 0.001. ns not significant, ud undetected, Arg1 Arginase 1.
Fig. 3
Fig. 3. Loss of Kdm2a in myeloid cells upregulates Pparγ and promotes fatty acid uptake and oxidation.
A A scatter plot representing the average gene expression levels (−log10) in KO relative to WT BMDMs upon IL-4 stimulation vs. fold changes (log2). Two biological replicates for WT mice and three for KO mice were included, and there were two mice for each biological replicate. B Heatmap showing the differentially expressed genes relevant to M2 program and genes related to lipid metabolism in IL-4-treated BMDMs. The data were generated from RNA deep sequencing as described. C RT-PCR analysis to confirm the relative mRNA abundance of Pparg, Cd36, Lpl, and Plin3 in BMDMs treated with vehicle or IL-4 for 6 h. Representative western blot results for analysis of Pparγ, CD36, and Cpt1a expression in BMDMs before and after IL-4 stimulation (D), and bar graphs (E) showing the mean expression levels resulted from three independent replications. F Uptake of BODIPY-labeled C12-fatty acids in BMDMs treated with or without IL-4 by flow cytometry analysis, and a bar graphic figure showing the mean data derived from four independent replications. G Representative FACS plots and quantitative data showing the uptake of BODIPY-labeled C12-fatty acids in BMDMs under indicated conditions. H OCR of BMDMs derived from WT and KO mice following 24 h of IL-4 stimulation, which was assessed before and after sequential treatment with oligomycin, FCCP, rotenone, and antimycin A. I Basal OCR (left) and SRC (right) in cells shown in (H), and all data were presented as mean derived from four independent experiments. The values are presented as mean ± SEM. Significance was determined by unpaired Student’s t test in (C, EG, I) (left panel) and by one-way ANOVA in (I) (right panel). *P < 0.05; **P < 0.01; ***P < 0.001. Cpt1a carnitine palmitoyltransferase 1a.
Fig. 4
Fig. 4. Loss of Kdm2a alleviates HFD-induced obesity and obesity-associated metabolic deterioration.
A Representative images for WT and KO mice fed with HFD or ND for 16 weeks. B Body weight changes for WT and KO mice during the course of HFD or ND induction. Representative pictures and bar graphs of epWAT (C) and scWAT (D) mass collected from WT and KO mice after 16 weeks of HFD or ND feeding. Representative H&E staining and lipid droplet surface quantification of epWAT (E) and scWAT (F) from HFD- or ND-fed WT and KO mice. G Blood glucose levels between WT and KO mice under fasting condition. H Plasma insulin levels determined after 16 weeks of HFD or ND feeding. I Results of intraperitoneal glucose tolerance tests (left) and the areas under curves (AUC) for blood glucose levels (right). J Results for the intraperitoneal insulin tolerance tests and areas above curves (AAC). K Results for analysis of triglyceride (TG) levels in the plasma. L Results for TG levels in the liver. Representative H&E staining and Oil Red O staining of liver sections originated from ND (M) or HFD (N) fed WT and KO mice. ND, n = 4 per group; HFD, n = 11 for WT mice and n = 10 for KO mice. Scale bars: 100 μm (E, F); 50μm (M, N). Original magnification: ×200 (E, F); ×400 (M, N). Values are expressed as mean ± SEM and unpaired Student’s t test was employed for data analysis. *P < 0.05; **P < 0.01; ***P < 0.001.
Fig. 5
Fig. 5. Kdm2a deficiency alleviates macrophage accumulation and reverses the M1–M2 imbalance of ATMs in mice following HFD challenge.
A Analysis of plasma cytokine levels between HFD-induced WT (n = 11) and KO (n = 10) mice. RT-PCR analyses of the mRNA abundance for the indicated genes in epWAT (B) and scWAT (C) (n = 6 per group). Representative images of immunostaining for F4/80 in epWAT (D) and scWAT (E) sections. The images were taken under ×400 magnification. Scale bar: 50 μm. Representative FACS plots, and the frequency and the number of ATMs in epWAT (F) and scWAT (G) in HFD-induced WT and KO mice. Representative FACS plots and quantitative data of M2 macrophages in epWAT (H) and scWAT (I) from HFD-induced WT and KO mice. Flow cytometry analysis of M1 macrophages in epWAT (J) and scWAT (K) from HFD-induced WT and KO mice. Left: a representative plot for flow cytometry; right: quantitative data resulted from all mice analyzed. n = 4 for each group (FK). Values are presented as mean ± SEM, and unpaired Student’s t test was used for statistical analysis. *P < 0.05; **P < 0.01; ***P < 0.001.
Fig. 6
Fig. 6. Macrophages deficient in Kdm2a increase energy expenditure and adaptive thermogenesis.
A Results for real-time recording of RER (left) and quantitative data (right) collected from four mice in each group for 24 h following 16 weeks of HFD induction (n = 4 per group). B Food intake (g) in WT and KO mice following 16 weeks of HFD induction measured in metabolic cages (n = 4 per group). RT-PCR results for analysis of thermogenic genes Cox5a, Ucp1, Cox7a, and Cox8b in BAT (C) and scWAT (D) from HFD challenged WT and KO mice (n = 6 for each group). E RT-PCR results for analysis of Ucp1 in the epWAT following 16 weeks of HFD challenge (n = 6 for each group). F Daily rectal temperature of mice housed under 4 °C condition (n = 6 per group). G Analysis of the weight for BAT collected from WT and KO mice after cold exposure (n = 6 per group). H Representative western blot results (left) and bar graphs (right) showing the expression levels for BAT TH and Ucp1 (n = 4 per group). I Relative mRNA abundance of Ucp1 in BAT of mice with (n = 6/group) or without cold stress (n = 3/group). Representative images of H&E staining (J) and Ucp1 IHC (K) of BAT sections with or without cold exposure (six images per mouse). Representative images of H&E staining (L) and Ucp1 IHC (M) of scWAT sections (six images per mouse). Scale bars: 50 μm (JM). Original magnification: ×400 (JM). Values are expressed as mean ± SEM, and unpaired Student’s t test was used for data analysis. *P < 0.05; **P < 0.01; ***P < 0.001. ns not significant.
Fig. 7
Fig. 7. Loss of Kdm2a promotes Pparγ transcription by inhibiting H3K36me2 demethylation along with chromatin remodeling.
A Average ATAC-seq signal distribution near the TSS. B Average ATAC-seq signals spanning the entire genome visualized in a TSS-centric manner. C Volcano plot of the differentially accessible regions (DARs) between WT and KO BMDMs treated with IL-4 for 6 h, as determined by ATAC-seq. DARs with log2 (fold change) ≥ 0.5, and a P value ≤ 0.05 in KO BMDMs are shown in red (increased accessibility) or blue (decreased accessibility). D Scatter plot of the correlation between DEGs vs. DARs. The number of genes in the quadrants is shown as indicated. E ATAC-seq bedgraph panels of the Pparg locus showing the peak locations relative to the TSS. The panels were compared with ATAC signals between WT and KO BMDMs following IL-4 stimulation. F ATAC peak strength (y-axis) for the selected peaks within the Pparg locus. G Results of ChIP-qPCR to compare H3K36me2 levels in the DARs of Pparg in WT and KO BMDMs treated with vehicle or IL-4 for 6 h. H Results of ChIP-qPCR to compare H3K36me2 levels in the DARs of Pparg in si-Control or si-Kdm2a transfected RAW264.7 cells after IL-4 stimulation for 6 h. I Enrichment of TF binding motifs in DARs of KO BMDMs gained or lost vs. WT BMDMs after IL-4 treatment. J ChIP-qPCR was performed for Stat6 in the Pparg DARs in WT and KO BMDMs treated with IL-4. K Representative western blot results (above) and a dotted line graph (below) showing the temporal expression of p-Stat6 in BMDMs after IL-4 stimulation. The data in (AF) and (I) were derived from two independent biological replicates, and there were two mice for each biological replicate. Data are representative of three independent experiments for figures (G, H, J, K). Values are presented as mean ± SEM. Statistical significance was determined by the unpaired Student’s t test in (B, FH, J, K). *P < 0.05; **P < 0.01.
Fig. 8
Fig. 8. Kdm2a directly targets Pparγ to regulate alternative activation of macrophages.
A OCR in WT and KO BMDMs stimulated with IL-4 for 24 h in the presence or absence of GW9662. B SRC in cells as shown in (A). C Western blot analysis of CD36 and Arg1 levels in WT and KO BMDMs under indicated culture conditions. D Flow cytometry analysis of the expression of F4/80, CD11b, and CD206 in BMDMs under indicated culture conditions. A bar graphic figure was employed to show the percentage of F4/80+CD11b+CD206+ cells in each group. Data were collected from four (A, B) or three independent experiments (C, D). Values are presented as mean ± SEM. Statistical significance was determined by the unpaired Student’s t test in (C), and by one-way ANOVA in (B, D). *P < 0.05; **P < 0.01; ***P < 0.001. ns not significant.

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