Tanycytic TSPO inhibition induces lipophagy to regulate lipid metabolism and improve energy balance

Autophagy. 2020 Jul;16(7):1200-1220. doi: 10.1080/15548627.2019.1659616. Epub 2019 Aug 30.

Abstract

Hypothalamic glial cells named tanycytes, which line the 3rd ventricle (3V), are components of the hypothalamic network that regulates a diverse array of metabolic functions for energy homeostasis. Herein, we report that TSPO (translocator protein), an outer mitochondrial protein, is highly enriched in tanycytes and regulates homeostatic responses to nutrient excess as a potential target for an effective intervention in obesity. Administration of a TSPO ligand, PK11195, into the 3V, and tanycyte-specific deletion of Tspo reduced food intake and elevated energy expenditure, leading to negative energy balance in a high-fat diet challenge. Ablation of tanycytic Tspo elicited AMPK-dependent lipophagy, breaking down lipid droplets into free fatty acids, thereby elevating ATP in a lipid stimulus. Our findings suggest that tanycytic TSPO affects systemic energy balance through macroautophagy/autophagy-regulated lipid metabolism, and highlight the physiological significance of TSPO in hypothalamic lipid sensing and bioenergetics in response to overnutrition.

Abbreviations: 3V: 3rd ventricle; ACAC: acetyl-Coenzyme A carboxylase; AGRP: agouti related neuropeptide; AIF1/IBA1: allograft inflammatory factor 1; AMPK: AMP-activated protein kinase; ARC: arcuate nucleus; Atg: autophagy related; Bafilo: bafilomycin A1; CAMKK2: calcium/calmodulin-dependent protein kinase kinase 2, beta; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CNS: central nervous system; COX4I1: cytochrome c oxidase subunit 4I1; FFA: free fatty acid; GFAP: glial fibrillary acidic protein; HFD: high-fat diet; ICV: intracerebroventricular; LAMP2: lysosomal-associated membrane protein 2; LD: lipid droplet; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MBH: mediobasal hypothalamus; ME: median eminence; MEF: mouse embryonic fibroblast; NCD: normal chow diet; NEFM/NFM: neurofilament medium; NPY: neuropeptide Y; OL: oleic acid; POMC: pro-opiomelanocortin-alpha; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; Rax: retina and anterior neural fold homeobox; RBFOX3/NeuN: RNA binding protein, fox-1 homolog (C. elegans) 3; RER: respiratory exchange ratio; siRNA: small interfering RNA; SQSTM1: sequestosome 1; TG: triglyceride; TSPO: translocator protein; ULK1: unc-51 like kinase 1; VCO2: carbon dioxide production; VMH: ventromedial hypothalamus; VO2: oxygen consumption.

Keywords: AMPK; TSPO; autophagy; energy balance; energy expenditure; food intake; hypothalamus; lipid metabolism; lipophagy; tanycyte.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinases / metabolism
  • Animals
  • Autophagy* / drug effects
  • Calcium / metabolism
  • Calcium-Calmodulin-Dependent Protein Kinase Kinase / metabolism
  • Energy Metabolism* / drug effects
  • Enzyme Activation / drug effects
  • Ependyma / metabolism
  • Ependymoglial Cells / drug effects
  • Ependymoglial Cells / metabolism*
  • Fatty Acids / metabolism
  • Hypothalamus / metabolism
  • Isoquinolines / pharmacology
  • Ligands
  • Male
  • Mice, Inbred C57BL
  • Mice, Obese
  • Mitochondria / drug effects
  • Mitochondria / metabolism
  • Receptors, GABA / metabolism

Substances

  • Bzrp protein, mouse
  • Fatty Acids
  • Isoquinolines
  • Ligands
  • Receptors, GABA
  • Calcium-Calmodulin-Dependent Protein Kinase Kinase
  • AMP-Activated Protein Kinases
  • Calcium
  • PK 11195

Grants and funding

This work was supported by the National Research Foundation of Korea (Grant No. 2017R1A2B2004483) and the DGIST R&D Program of the Ministry of Science and ICT (Grant No. 19-BD-0402).