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SBP2 deficiency in adipose tissue macrophages drives insulin resistance in obesity

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Science Advances  14 Aug 2019:
Vol. 5, no. 8, eaav0198
DOI: 10.1126/sciadv.aav0198
  • Fig. 1 SBP2 expression in ATMs was reduced during obesity.

    (A) Previous human subject data were collected from a Gene Expression Omnibus dataset (GSE54350). Expression of SBP2 was retrieved, and a significant difference was found between obese individuals with or without diabetes. Mice were fed an HFD for 2, 4, and 8 weeks, and (B) the expression of SBP2, (C) the expression of anti-oxidative selenoproteins GPX4 and TXNRD1, and (D) the infiltration of CD11b+F4/80+ cells into adipose tissue were measured. The ingWAT, interscapular BAT, and epiWAT were collected from mice fed with HFD for 4 weeks. (E) The expression of SBP2 was measured in different adipose tissues; epiWAT from mice fed with HFD for 8 weeks was collected and separated using the Percoll protocol. (F) Expression of SBP2 in adipose tissue of mice was correlated with the abundance of CD11b+F4/80+ proinflammatory macrophages. (G) Adipocytes, F4/80, and F4/80+ mononuclear cells were collected to measure SBP2 expression. SBP2 showed significant lower expression in F4/80+ ATMs but not adipocytes or F4/80 Stroma vascular fraction (SVF) cells. *P < 0.05, **P < 0.01, ***P < 0.001. not significant (n.s.), not significant.

  • Fig. 2 Loss of SBP2 induced inflammations in metabolically activated ATMs and inflammasome-associated IL-1β production.

    In vitro metabolic activation of BMDMs was induced by treatment of 10 mM glucose, 10 μM insulin, or 500 μM bovine serum albumin–conjugated palmitate for 24 hours. Only palmitate treatment could suppress (A) mRNAs and (B) protein expression of SBP2 in metabolically activated macrophages (MMe). Overexpression of SBP2 in MMe (C) suppressed CD11c presentation without significant change on CD206 (D) and shifted MMe from the expression of proinflammatory cytokine profile. (E) Mice with ATM-specific knockdown of SBP2 exhibited higher serum IL-1β without potent change in IL1Ra levels. (F) Sorted ATMs from DIO mice with SBP2 knockdown, as well as (G) in vitro culture of MMe with SBP2 knockdown, showed higher IL-1β secretion. (H) Overexpression of SBP2OE in MMe significantly reduced intracellular ROS level, which could be minimally reduced by the presence of an IL-1β–neutralizing antibody, and (I) sorted ATMs from DIO mice with SBP2 knockdown, as well as (J) in vitro culture of MMe with SBP2 knockdown, showed a higher level of inflammasome activation. ATM-specific knockdown of SBP2 in HFD-fed mice increased both (K) the local proliferation and (L) infiltration of macrophages, and (M) infiltrated macrophages had similar expression level of SBP2 with resident macrophages, both of which had significantly lower SBP2 expression in ATMs than lean mice. *P < 0.05, **P < 0.01, ***P < 0.001.

  • Fig. 3 Loss of SBP2 in obesity exacerbated insulin resistance and adipogenesis.

    (A) Knockdown of SBP2 had minimal effects on the body weight of mice fed with either normal chow diet (NCD) or HFD but (B) increased adipose tissue weight gain in DIO mice. Knockdown of SBP2 in DIO mice (C) elevated FBG, reduced (D) glucose tolerance and (E) insulin sensitivity, (F) increased serum HbA1c levels, and (G) blunted adipose tissue Akt signal activity in response to insulin. SBP2 knockdown in ATMs of DIO mice (H) promoted ATM infiltration, which (I) extended sizes of adipocytes and (J) induced gene expression associated with lipogenesis. *P < 0.05, **P < 0.01, ***P < 0.001. SREBP1c, sterol regulatory element–binding protein 1; Dgat1, diglyceride acyltransferase 1. Scale bars, 50 µm.

  • Fig. 4 Overexpression of SBP2 improved insulin sensitivity and suppressed adipogenesis in obese mice.

    (A) SBP2 restoration induced (B) expression of M2-like genes instead of M1-like ones in sorted ATMs of db/db mice. SBP2 overexpression (C) did not change the body weight but (D) reduced adipose tissue weight, (E) improved FBG levels, (F) glucose intolerance and (G) insulin sensitivity, (H) serum HbA1c levels, (I) sensitized adipose insulin-responsive Akt pathway, and (J) reduced macrophage infiltration in adipose tissue. (K) Reexpression of SBP2 reduced M1-like macrophages but increased M2-like populations. (L) Sorted SBP2-overexpressing ATMs exhibited reduced inflammasome activation. SBP2 overexpression induced (M) smaller adipocyte diameters and (N) reduced expression of lipogenesis-associated genes. *P < 0.05, **P < 0.01, ***P < 0.001.

  • Fig. 5 A holistic formula TNTL targeting SBP2 in ATMs improved insulin resistance in obese mice.

    (A) SBP2 expression in M1-like BMDMs was notably higher after oral (per os, p.o.) treatment with TNTL. (B and C) TNTL treatment induced SBP2 expression in ATMs of db/db mice. (D) Macrophage-specific knockdown of SBP2 in TNTL-treated mice abrogated the effects of TNTL. (E) TNTL treatment did not affect body weight gain but (F) reduced adipose tissue weight. Knockdown of SBP2 in ATMs abrogated the therapeutic effect of TNTL on (G) FBG levels, (H) glucose intolerance, (I) insulin sensitivity, (J) serum HbA1c levels, and (K) sensitized adipose insulin-responsive Akt pathway. *P < 0.05, **P < 0.01, ***P < 0.001.

  • Fig. 6 TNTL improved hyperglycemia and insulin resistance in patients with diabetes.

    Patients with T2D receiving a 3-month treatment of TNTL showed significant improvement in (A) FBG, (B) 2-hour postprandial glucose, and (C) plasma HbA1c levels. Effect of TNTL was not associated with (D) gender difference and (E) age. (F) The regulatory scheme of SBP2 in ATM inflammation during obesity. *P < 0.05.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaav0198/DC1

    Supplemental Experimental Details

    Fig. S1. Determination of SBP2 expression in SBP2 tissue.

    Fig. S2. SBP2 expression controls the phenotype polarization of ATMs.

    Fig. S3. SBP2 overexpression had no significant effect on the lysosome exocytosis of MMe.

    Fig. S4. Glucan-mediated macrophage-targeted delivery specifically suppressed SBP2 in ATMs.

    Fig. S5. SBP2 suppressed activation of caspase-1 by the inflammasome.

    Fig. S6. Eight-week knockdown of SBP2 in ATMs accelerated insulin resistance in DIO mice but not in diabetic db/db mice (n = 6).

    Fig. S7. SBP2 knockdown in ATMs produced a more pronounced effect in male mice than female mice.

    Fig. S8. Chemical and safety analysis of TNTL.

    Table S1. Basic information of patients observed in the study.

    Table S2. Primers to be used for quantitative reverse transcription polymerase chain reaction.

  • Supplementary Materials

    This PDF file includes:

    • Supplemental Experimental Details
    • Fig. S1. Determination of SBP2 expression in SBP2 tissue.
    • Fig. S2. SBP2 expression controls the phenotype polarization of ATMs.
    • Fig. S3. SBP2 overexpression had no significant effect on the lysosome exocytosis of MMe.
    • Fig. S4. Glucan-mediated macrophage-targeted delivery specifically suppressed SBP2 in ATMs.
    • Fig. S5. SBP2 suppressed activation of caspase-1 by the inflammasome.
    • Fig. S6. Eight-week knockdown of SBP2 in ATMs accelerated insulin resistance in DIO mice but not in diabetic db/db mice (n = 6).
    • Fig. S7. SBP2 knockdown in ATMs produced a more pronounced effect in male mice than female mice.
    • Fig. S8. Chemical and safety analysis of TNTL.
    • Table S1. Basic information of patients observed in the study.
    • Table S2. Primers to be used for quantitative reverse transcription polymerase chain reaction.

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