Mild mitochondrial uncoupling does not affect mitochondrial biogenesis but downregulates pyruvate carboxylase in adipocytes: role for triglyceride content reduction

Abstract

De Pauw A, Demine S, Tejerina S, Dieu M, Delaive E, Kel A, Renard P, Raes M, Arnould T. Mild mitochondrial uncoupling does not affect mitochondrial biogenesis but downregulates pyruvate carboxylase in adipocytes: role for triglyceride content reduction. Am J Physiol Endocrinol Metab 302: E1123-E1141, 2012. First published February 21, 2012 doi:10.1152/ajpendo.00117.2011In adipocytes, mitochondrial uncoupling is known to trigger a triglyceride loss comparable with the one induced by TNF␣, a proinflammatory cytokine. However, the impact of a mitochondrial uncoupling on the abundance/composition of mitochondria and its connection with triglyceride content in adipocytes is largely unknown. In this work, the effects of a mild mitochondrial uncoupling triggered by FCCP were investigated on the mitochondrial population of 3T3-L1 adipocytes by both quantitative and qualitative approaches. We found that mild mitochondrial uncoupling does not stimulate mitochondrial biogenesis in adipocytes but induces an adaptive cell response characterized by quantitative modifications of mitochondrial protein content. Superoxide anion radical level was increased in mitochondria of both TNF␣-and FCCP-treated adipocytes, whereas mitochondrial DNA copy number was significantly higher only in TNF␣-treated cells. Subproteomic analysis revealed that the abundance of pyruvate carboxylase was reduced significantly in mitochondria of TNF␣-and FCCP-treated adipocytes. Functional study showed that overexpression of this major enzyme of lipid metabolism is able to prevent the triglyceride content reduction in adipocytes exposed to mitochondrial uncoupling or TNF␣. These results suggest a new mechanism by which the effects of mitochondrial uncoupling might limit triglyceride accumulation in adipocytes.adipocytes; carbonyl cyanide p-trifluoromethoxyphenylhydrazone; tumor necrosis factor-␣; mitoproteome OBESITY RESULTS LARGELY FROM A CHRONICALLY POSITIVE energy balance. Therefore, reducing body energy intake and increasing energy expenditure are two approaches that have been translated into strategies to limit fat accumulation. Because mitochondria play a critical role in the process of energy expenditure, the alteration of oxidative phosphorylation (OX-PHOS) efficiency through OXPHOS uncoupling from ATP production in white adipocytes has been considered as an attractive approach to fight obesity (7, 69). In other words, uncoupling increases cellular metabolic demand since uncoupling OXPHOS lowers ATP production and increases the demand for reducing equivalents to restore/maintain mitochondrial membrane potential, thereby increasing substrate catabolism, which would theoretically decrease triglyceride (TG) stores in adipocytes. Indeed, although mitochondrial dysfunction could represent a major cause of lipid metabolism disorders and pathological triglyceride accumulation in several cell lines (50, 75), we and others have shown that mitochondrial uncoupling in adipocytes triggers lipolysis, limits fatty acid synthesis, and leads to a reduction in TG ...

Mapping metabolic changes by noninvasive, multiparametric, high-resolution imaging using endogenous contrast

“…5 , K and L; fig. S8D; and Table 1 ) is consistent with mitochondrial truncation and branching to efficiently surround the lipid droplets and facilitate lipid biosynthesis compared to the more extended mitochondrial networks of the undifferentiated human MSCs ( 71 ).…”

Mitochondrial dysfunction in white adipose tissue

“…Such effects result in a state of “oxidative-stress”, which further ensues a downregulation in PPARγ and adiponectin [33]. In contrast, De Pauw and colleagues noted that mild uncoupling of 3T3-L1 adipocyte mitochondria, as triggered by FCCP or TNFα treatment, did increase ROS production, however did not alter mitochondrial biogenesis [34]. Rather the abundance of adipocyte pyruvate carboxylase, a major enzyme that participates in de novo fatty acid synthesis and glyceroneogenesis, was significantly downregulated; this was accompanied with a reduction in adipocyte triglyceride (TG) content [34].…”

“…In contrast, De Pauw and colleagues noted that mild uncoupling of 3T3-L1 adipocyte mitochondria, as triggered by FCCP or TNFα treatment, did increase ROS production, however did not alter mitochondrial biogenesis [34]. Rather the abundance of adipocyte pyruvate carboxylase, a major enzyme that participates in de novo fatty acid synthesis and glyceroneogenesis, was significantly downregulated; this was accompanied with a reduction in adipocyte triglyceride (TG) content [34]. This study presents a new and intriguing mechanism whereby treatments that uncouple mitochondria may serve to effectively limit TG accumulation in adipocytes, specifically by mitigating the pro-lipogenic properties of pyruvate carboxylase [34].…”

“…Rather the abundance of adipocyte pyruvate carboxylase, a major enzyme that participates in de novo fatty acid synthesis and glyceroneogenesis, was significantly downregulated; this was accompanied with a reduction in adipocyte triglyceride (TG) content [34]. This study presents a new and intriguing mechanism whereby treatments that uncouple mitochondria may serve to effectively limit TG accumulation in adipocytes, specifically by mitigating the pro-lipogenic properties of pyruvate carboxylase [34]. Future studies will have to examine more closely whether such effects in adipocytes are beneficial in minimizing obesity-induced lipotoxicity.…”

Mild mitochondrial uncoupling induces HSL/ATGL‐independent lipolysis relying on a form of autophagy in 3T3‐L1 adipocytes

“…An attractive strategy to limit fat accumulation and stimulate energy expenditure in adipose tissues (Harper, Dickinson, & Brand, ) involves triggering a mild/controlled/targeted and chronic mitochondrial uncoupling in these tissues, as long as it is accompanied by the stimulation of free fatty acid (FFA) β‐oxidation in other tissues such as heart, muscles, liver kidney, and brown adipose tissue (Harper et al, ). In 3T3‐L1 adipocytes, it has been shown that a mild uncoupling of mitochondria limits fat accumulation by reducing the expression of pyruvate carboxylase, limiting TAG, and fatty acid (FA) synthesis (De Pauw et al, ) and increasing lipolysis (Si, Palani, Jayaraman, & Lee, ; Tejerina et al, ). However, the molecular mechanisms triggered by mitochondrial uncoupling leading to the activation of lipolysis remain poorly understood.…”