Elevated autophagy gene expression in adipose tissue of obese humans: A potential non-cell-cycle-dependent function of E2F1

Yulia Haim; Matthias Blüher; Noa Slutsky; Nir Goldstein; Nora Klöting; Ilana Harman-Boehm; Boris Kirshtein; Doron Ginsberg; Martin Gericke; Esther Guiu Jurado; Julia Kovsan; Tanya Tarnovscki; Leonid Kachko; Nava Bashan; Yiftach Gepner; Iris Shai; Assaf Rudich

doi:10.1080/15548627.2015.1094597

Elevated autophagy gene expression in adipose tissue of obese humans: A potential non-cell-cycle-dependent function of E2F1

Autophagy. 2015 Nov 2;11(11):2074-2088. doi: 10.1080/15548627.2015.1094597.

Authors

Yulia Haim¹, Matthias Blüher², Noa Slutsky¹, Nir Goldstein¹, Nora Klöting², Ilana Harman-Boehm³, Boris Kirshtein³, Doron Ginsberg⁴, Martin Gericke⁵, Esther Guiu Jurado², Julia Kovsan¹, Tanya Tarnovscki¹, Leonid Kachko³, Nava Bashan¹, Yiftach Gepner⁶, Iris Shai⁶, Assaf Rudich^{1

7}

Affiliations

¹ a Department of Clinical Biochemistry and Pharmacology ; Faculty of Health Sciences; Ben-Gurion University of the Negev ; Beer-Sheva , Israel.
² b Department of Medicine ; University of Leipzig ; Leipzig , Germany.
³ c Soroka Academic Medical Center and Faculty of Health Sciences; Ben-Gurion University of the Negev ; Beer-Sheva , Israel.
⁴ d The Mina and Everard Goodman Faculty of Life Science; Bar-Ilan University ; Ramat Gan , Israel.
⁵ e Institute of Anatomy; University of Leipzig ; Leipzig , Germany.
⁶ f Department of Epidemiology ; Ben-Gurion University of the Negev ; Beer-Sheva , Israel.
⁷ g National Institute of Biotechnology in the Negev; Ben-Gurion University of the Negev ; Beer-Sheva , Israel.

Abstract

Autophagy genes' expression is upregulated in visceral fat in human obesity, associating with obesity-related cardio-metabolic risk. E2F1 (E2F transcription factor 1) was shown in cancer cells to transcriptionally regulate autophagy. We hypothesize that E2F1 regulates adipocyte autophagy in obesity, associating with endocrine/metabolic dysfunction, thereby, representing non-cell-cycle function of this transcription factor. E2F1 protein (N=69) and mRNA (N=437) were elevated in visceral fat of obese humans, correlating with increased expression of ATG5 (autophagy-related 5), MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 β), but not with proliferation/cell-cycle markers. Elevated E2F1 mainly characterized the adipocyte fraction, whereas MKI67 (marker of proliferation Ki-67) was elevated in the stromal-vascular fraction of adipose tissue. In human visceral fat explants, chromatin-immunoprecipitation revealed body mass index (BMI)-correlated increase in E2F1 binding to the promoter of MAP1LC3B, but not to the classical cell cycle E2F1 target, CCND1 (cyclin D1). Clinically, omental fat E2F1 expression correlated with insulin resistance, circulating free-fatty-acids (FFA), and with decreased circulating ADIPOQ/adiponectin, associations attenuated by adjustment for autophagy genes. Overexpression of E2F1 in HEK293 cells enhanced promoter activity of several autophagy genes and autophagic flux, and sensitized to further activation of autophagy by TNF. Conversely, mouse embryonic fibroblast (MEF)-derived adipocytes from e2f1 knockout mice (e2f1^-/-) exhibited lower autophagy gene expression and flux, were more insulin sensitive, and secreted more ADIPOQ. Furthermore, e2f1^-/- MEF-derived adipocytes, and autophagy-deficient (by Atg7 siRNA) adipocytes were resistant to cytokines-induced decrease in ADIPOQ secretion. Jointly, upregulated E2F1 sensitizes adipose tissue autophagy to inflammatory stimuli, linking visceral obesity to adipose and systemic metabolic-endocrine dysfunction.

Keywords: E2F1; adipose tissue; autophagy; obesity; stress response; transcriptional regulation.