GSK3B induces autophagy by phosphorylating ULK1

Unc-51-like autophagy activating kinase 1 (ULK1), a mammalian homolog of the yeast kinase Atg1, has an essential role in autophagy induction. In nutrient and growth factor signaling, ULK1 activity is regulated by various posttranslational modifications, including phosphorylation, acetylation, and ubiquitination. We previously identified glycogen synthase kinase 3 beta (GSK3B) as an upstream regulator of insulin withdrawal-induced autophagy in adult hippocampal neural stem cells. Here, we report that following insulin withdrawal, GSK3B directly interacted with and activated ULK1 via phosphorylation of S405 and S415 within the GABARAP-interacting region. Phosphorylation of these residues facilitated the interaction of ULK1 with MAP1LC3B and GABARAPL1, while phosphorylation-defective mutants of ULK1 failed to do so and could not induce autophagy flux. Furthermore, high phosphorylation levels of ULK1 at S405 and S415 were observed in human pancreatic cancer cell lines, all of which are known to exhibit high levels of autophagy. Our results reveal the importance of GSK3B-mediated phosphorylation for ULK1 regulation and autophagy induction and potentially for tumorigenesis.

Metabolic effects of an SGLT2 inhibitor (dapagliflozin) during a period of acute insulin withdrawal and development of ketoacidosis in people with type 1 diabetes.

Objective: To determine the effect of SGLT₂ inhibitor dapagliflozin on glucose flux, lipolysis and ketone body concentrations during insulin withdrawal in people with type 1 diabetes. <p> </p> <p>Research Design and Methods: A double-blind placebo controlled crossover study with a 4-week wash out period was performed in 12 people with type 1 diabetes using insulin pump therapy. Participants received dapagliflozin or placebo in random order for 7 days. Stable isotopes were infused to measure the rate of glucose production (Ra), disappearance (Rd) and lipolysis. At isotopic steady state insulin was withdrawn and the study terminated after 600 minutes or earlier if blood glucose reached 18mmol/L, bicarbonate <15mmol/L, venous pH <7.35 or capillary ketones >5.0 mmol/L. </p> <p><br></p><p>Results: At baseline, glucose Ra was significantly higher with dapagliflozin than placebo. Following insulin withdrawal, plasma glucose concentrations at the end point were significantly lower with dapagliflozin than placebo and AUC_0-180minglucose Rd and AUC_0-180minβ-hydroxybutyrate (BOHB) were significantly higher. There was a small but significantly higher AUC_0-180minglycerol Ra (measure of lipolysis) with dapagliflozin. Non-esterified fatty acid concentrations were not different between treatments.</p> <p>When divided by BMI>27 and <27kg/m², basal glucose Ra and BOHB, and AUC_0-180minglycerol Ra were significantly higher in the low BMI group with dapaglifozin versus placebo treatment.</p> <p><br></p><p>Conclusions: During insulin withdrawal the increase in BOHB with dapaglifozin may be partially due to increased lipolysis. However reduced renal excretion, reduced BOHB uptake by peripheral tissues or a metabolic switch to increase ketogenesis within the liver may also play a role. <u></u></p>

Metabolic effects of an SGLT2 inhibitor (dapagliflozin) during a period of acute insulin withdrawal and development of ketoacidosis in people with type 1 diabetes.

Objective: To determine the effect of SGLT₂ inhibitor dapagliflozin on glucose flux, lipolysis and ketone body concentrations during insulin withdrawal in people with type 1 diabetes. <p> </p> <p>Research Design and Methods: A double-blind placebo controlled crossover study with a 4-week wash out period was performed in 12 people with type 1 diabetes using insulin pump therapy. Participants received dapagliflozin or placebo in random order for 7 days. Stable isotopes were infused to measure the rate of glucose production (Ra), disappearance (Rd) and lipolysis. At isotopic steady state insulin was withdrawn and the study terminated after 600 minutes or earlier if blood glucose reached 18mmol/L, bicarbonate <15mmol/L, venous pH <7.35 or capillary ketones >5.0 mmol/L. </p> <p><br></p><p>Results: At baseline, glucose Ra was significantly higher with dapagliflozin than placebo. Following insulin withdrawal, plasma glucose concentrations at the end point were significantly lower with dapagliflozin than placebo and AUC_0-180minglucose Rd and AUC_0-180minβ-hydroxybutyrate (BOHB) were significantly higher. There was a small but significantly higher AUC_0-180minglycerol Ra (measure of lipolysis) with dapagliflozin. Non-esterified fatty acid concentrations were not different between treatments.</p> <p>When divided by BMI>27 and <27kg/m², basal glucose Ra and BOHB, and AUC_0-180minglycerol Ra were significantly higher in the low BMI group with dapaglifozin versus placebo treatment.</p> <p><br></p><p>Conclusions: During insulin withdrawal the increase in BOHB with dapaglifozin may be partially due to increased lipolysis. However reduced renal excretion, reduced BOHB uptake by peripheral tissues or a metabolic switch to increase ketogenesis within the liver may also play a role. <u></u></p>