Salt-inducible kinase 2 regulates TFEB and is required for autophagic flux in adipocytes

Dysregulation of Autophagy has been observed in obesity and type 2 diabetes. Salt-inducible kinase 2 (SIK2), a member of the AMPK-related kinase family, is downregulated in adipocytes from obese or Insulin resistant individuals and was previously demonstrated to regulate Autophagy in Cancer and normal cell lines. The aim of this study was thus to investigate a potential role of SIK2 in the regulation of adipocyte Autophagy. To do so, SIK2 siRNA silencing or SIKs pharmacological inhibition of SIK2 was employed in murine differentiated 3T3-L1 adipocytes and autophagic flux was monitored. Our data indicate that SIK2 is required for both autophagic flux and expression of TFEB, the transcription factor that regulates Autophagy, in adipocytes. The effect of SIK2 on autophagic flux occurs before the regulation of TFEB protein levels, suggesting different mechanisms whereby SIK2 stimulates Autophagy. This study broadens the current knowledge on Autophagy regulation and SIK2 function in adipocytes.