Metformin adapts its cellular effects to bioenergetic status in a model of metabolic dysfunction

Abstract

Thermal injury induces a complex immunometabolic response, characterized by hyperglycemia, extensive inflammation and persistent hypermetabolism. It has been suggested that attenuation of the hypermetabolic response is beneficial for patient wellbeing. To that effect, metformin represents an attractive therapeutic agent, as its effects on glycemia, inflammation and bioenergetics can improve outcomes in burn patients. Therefore, we studied metformin and its effects on mitochondrial bioenergetics in a murine model of thermal injury. We set out to determine the impact of this agent on mitochondrial hypermetabolism (adult mice) and mitochondrial dysfunction (aged mice). Seahorse respirometry complimented by in-gel activity assays were used to elucidate metformin’s cellular mechanism. We found that metformin exerts distinctly different effects, attenuating the hypermetabolic mitochondria of adult mice while significantly improving mitochondrial bioenergetics in the aged mice. Furthermore, we observed that these changes occur both with and without adenosine monophosphate kinase (AMPK) activation, respectively, and analyzed damage markers to provide further context for metformin’s beneficial actions. We suggest that metformin has a dual role following trauma, acting via both AMPK-dependent and independent pathways depending on bioenergetic status. These findings help further our understanding of metformin’s biomolecular effects and support the continued use of this drug in patients.

The Anti-Diabetic Drug Metformin Rescues Aberrant Mitochondrial Activity and Restrains Oxidative Stress in a Female Mouse Model of Rett Syndrome

“…As the main difference from the Fragile X study concerns the age of the animals (two months vs about 1 year in the present study), it is conceivable that the 200 mg/kg may have provided convulsions in both WT and RTT mice due to their advanced age. Consistently, previous studies have demonstrated that metformin exerts different effects depending on the age of the mice [8]. Furthermore, Martin-Montalvo and colleagues [6] similarly observed that chronic high doses of metformin in old mice can be toxic.…”

“…Chronic treatment with metformin in fact improves mitochondrial function and increases antioxidant protection. Consistent with the capability of metformin to pass the blood-brain barrier, these treatment effects have been evidenced both in the periphery and in the brain [7][8][9][10]. The exact nature of the interaction between metformin and mitochondria is still poorly characterized [11,12].…”

“…Interestingly, metformin treatment did not boost pathways related to mitochondrial biogenesis and antioxidant response in WT mice. Indeed, previous studies have demonstrated that metformin's effects on mitochondrial dynamics are strictly dependent on the initial bioenergetic status [8]. How metformin adapts its effects is however still unclear.…”

Metformin prevents the pathological browning of subcutaneous white adipose tissue

“…Upon completion, the gel was equilibrated in reaction buffer (25 mM Tris-HCl, 5 mM MgCl 2 , pH 7.4) for 15–30 min. Equal loading was assured by Coomassie blue staining, as described [27]. Complex I was detected by the addition of 5 mM KCN, 1 mM NADH and 0.4 mg/mL iodonitrotetrazolium chloride.…”

“…To characterize protein expression, western blots were performed. Following SDS-PAGE of iWAT or scWAT lysate (30 μg), proteins were transferred using a Trans-Blot Turbo Transfer System (Bio-Rad) [27]. Upon completion, the nonspecific binding sites on the membrane were blocked using 5% (w/v) non-fat skim milk for 1 h. The membrane was then washed twice in TTBS (12.1 g Tris, 40 g NaCl, 2% Tween 20; pH 7.6 at 4 °C) for 5 min.…”