SNAP23 regulates BAX-dependent adipocyte programmed cell death independently of canonical macroautophagy
Daorong Feng, … , Richard N. Kitsis, Jeffrey E. Pessin
Daorong Feng, … , Richard N. Kitsis, Jeffrey E. Pessin
Published August 13, 2018
Citation Information: J Clin Invest. 2018;128(9):3941-3956. https://doi.org/10.1172/JCI99217.
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Research Article Cell biology Metabolism

SNAP23 regulates BAX-dependent adipocyte programmed cell death independently of canonical macroautophagy

Abstract

The t-SNARE protein SNAP23 conventionally functions as a component of the cellular machinery required for intracellular transport vesicle fusion with target membranes and has been implicated in the regulation of fasting glucose levels, BMI, and type 2 diabetes. Surprisingly, we observed that adipocyte-specific KO of SNAP23 in mice resulted in a temporal development of severe generalized lipodystrophy associated with adipose tissue inflammation, insulin resistance, hyperglycemia, liver steatosis, and early death. This resulted from adipocyte cell death associated with an inhibition of macroautophagy and lysosomal degradation of the proapoptotic regulator BAX, with increased BAX activation. BAX colocalized with LC3-positive autophagic vacuoles and was increased upon treatment with lysosome inhibitors. Moreover, BAX deficiency suppressed the lipodystrophic phenotype in the adipocyte-specific SNAP23-KO mice and prevented cell death. In addition, ATG9 deficiency phenocopied SNAP23 deficiency, whereas ATG7 deficiency had no effect on BAX protein levels, BAX activation, or apoptotic cell death. These data demonstrate a role for SNAP23 in the control of macroautophagy and programmed cell death through an ATG9-dependent, but ATG7-independent, pathway regulating BAX protein levels and BAX activation.

Authors

Daorong Feng, Dulguun Amgalan, Rajat Singh, Jianwen Wei, Jennifer Wen, Tszki Peter Wei, Timothy E. McGraw, Richard N. Kitsis, Jeffrey E. Pessin

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Figure 1

Adipocyte-specific SNAP23-KO mice display severe lipodystrophy associated with liver steatosis and adipose tissue inflammation.

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Adipocyte-specific SNAP23-KO mice display severe lipodystrophy associate...
(A) Thirty-two-week-old male KO mice had extended abdomens (first panel on left) with enlarged, pale livers (star in second panel from left), loss of epididymal adipose tissue (triangles in second panel from left), subcutaneous adipose tissue (inside outlined shapes in third panel from left), perirenal adipose tissue (inside outlined shapes in fourth panel from left), and interscapular BAT (circle in last panel on right). (B) Plasma glucose, (C) leptin, (D) adiponectin, and (E) triglyceride levels were determined as described in Methods. (F) Hepatic triglyceride content was normalized to total protein levels (n = 5 WT mice and n = 5 KO mice). (G) Echo-MRI analysis of total fat mass in Snap23fl/fl (WT) and adipocyte-specific SNAP23-deficient (KO) mice at 2, 3, 4, 8, 12, 16, 24, and 32 weeks of age (n = 5–10 mice). (H) Perilipin immunofluorescence (red) and DAPI staining (blue) for nuclei in epididymal adipose tissue from 4-week-old WT and KO mice. Arrows indicate perilipin-depleted cells. Scale bars: 40 μm. (I) Quantification of perilipin-depleted cells was performed on epididymal adipose tissue (epi) from 4-week-old mice and subcutaneous adipose tissue (s.c.) from 1-week-old mice. (J) Epididymal adipose tissue from 4-week-old WT and KO mice was fixed, stained with H&E, and examined by light microscopy. Arrowheads indicate selected areas of inflammation and the presence of crown-like structures. Scale bars: 50 μm. (K) The relative diameter of the morphologically normal–appearing adipocytes from panel J was quantified (n = 500 cells). (L) Epididymal adipose tissue from 4-week-old WT and KO mice was extracted and subjected to qRT-PCR to determine the indicated mRNA levels (n = 5 WT mice and n = 5 KO mice). All data represent the mean ± SEM. *P < 0.05 and ***P < 0.001, by Student’s t test.