Fibroblast growth factor 21 enhances learning and memory performance in mice by regulating hippocampal L-lactate homeostasis.

Fibroblast growth factor 21 (FGF21) is one endogenous metabolic molecule that functions as a regulator in glucose and lipid homeostasis. However, the effect of FGF21 on L-lactate homeostasis and its mechanism remains unclear until now. Forty-five Six-week-old male C57BL/6 mice were divided into three groups: control, L-lactate, and FGF21 (1.5 mg/kg) groups. At the end of the treatment, nuclear magnetic resonance-based metabolomics, and key proteins related to L-lactate homeostasis were determined respectively to evaluate the efficacy of FGF21 and its mechanisms. The results showed that, compared to the vehicle group, the L-lactate-treated mice displayed learning and memory performance impairments, as well as reduced hippocampal ATP and NADH levels, but increased oxidative stress, mitochondrial dysfunction, and apoptosis, which suggesting inhibited L-lactate-pyruvate conversion in the brain. Conversely, FGF21 treatment ameliorated the L-lactate accumulation state, accompanied by restoration of the learning and memory defects, indicating enhanced L-lactate uptake and utilization in hippocampal neurons. We demonstrated that maintaining constant L-lactate-pyruvate flux is essential for preserving neuronal bioenergetic and redox levels. FGF21 contributed to preparing the brain for situations of high availability of L-lactate, thus preventing neuronal vulnerability in metabolic reprogramming.

Fibroblast growth factor 21 protects the liver from apoptosis in a type 1 diabetes mouse model via regulating L-lactate homeostasis.

AIMS/HYPOTHESIS: Fibroblast growth factor 21 (FGF21) is a hepatokine with pleiotropic effects on glucose and lipid metabolic homeostasis. Here, we aimed to elucidate the mechanisms underlying the protective effects of FGF21 on L-lactate homeostasis and liver lesions in a type 1 diabetes mellitus (T1DM) mice model. METHODS: Six-week-old male C57BL/6 mice were divided into control, T1DM, and FGF21 groups. We also examined hepatic apoptotic signaling and functional indices in wild-type and hydroxycarboxylic acid receptor 1 (HCA1) knockout mice with T1DM or long-term L-lactate exposure. After preincubation of high glucose- or L-lactate treated hepatic AML12 cells, L-lactate uptake, apoptosis, and monocarboxylic acid transporter 2 (MCT2) expression were investigated. RESULTS: In a mouse model of T1DM, hepatic FGF21 expression was downregulated by approximately 1.5-fold at 13 weeks after the hyperglycemic insult. In vivo administration of exogenous FGF21 (2 mg/kg) to diabetic or L-lactate-infused mice significantly prevented hepatic oxidative stress and apoptosis by activating extracellular signal-regulated kinase (ERK)1/2, p38 mitogen-activated protein kinase (MAPK) and AMP-activated protein kinase (AMPK) pathways. HCA1-KO mice were less susceptible to diabetes- and L-lactate-induced hepatic apoptosis and dysfunction. In addition, inhibition of PI3K-mTOR activity revealed that FGF21 prevented L-lactate-induced Cori cycle alterations and hepatic apoptosis by upregulating MCT2 protein translation. CONCLUSIONS/INTERPRETATION: These results demonstrate that L-lactate homeostasis may be a therapeutic target for T1DM-related hepatic dysfunction. The protective effects of FGF21 on hepatic damage were associated with its ability to ameliorate MCT2-dependent Cori cycle alterations and prevent HCA1-mediated inhibition of ERK1/2, p38 MAPK, and AMPK signaling.

A combined metabolomics and molecular biology approach to reveal hepatic injury and underlying mechanisms after chronic l-lactate exposure in mice.

This study aimed to explore whether chronic l-lactate exposure could affect the peripheral tissues of mice and to determine the underlying pathogenesis. Herein, male C57BL/6 mice were divided into control and l-lactate groups. After l-lactate treatment for eight weeks (1 g/kg), metabolic changes in liver, kidney, muscle, and serum samples were determined by 1H nuclear magnetic resonance (1H NMR)-based metabolomics. Additionally, organ function was evaluated by serum biochemical and histopathological examinations. Reactive oxygen species (ROS) levels were measured using dihydroethidium staining; levels of signals involved in lactate metabolism and ROS-related pathways were detected using western blotting or polymerase chain reaction. Apoptosis was detected by TUNEL-fluorescence staining. Metabolomic analysis revealed that l-lactate mice showed decreased levels of glutathione (GSH), taurine, ATP, and increased glucose content, compared to control mice. Furthermore, l-lactate mice presented significantly higher serum levels of alanine aminotransferase and aspartate aminotransferase and increased glycogen content in hepatic tissues, compared to control mice. l-lactate mice also had a greater number of apoptotic nuclei in the livers than controls. Moreover, l-lactate exposure reduced mRNA and protein levels of superoxide dismutase-2 and c-glutamylcysteine ligase, elevated levels of cytochrome P450 2E1 and NADPH oxidase-2, and increased the protein expressions of LDHB, Bax/Bcl-2, cleaved caspase-3, and sirtuin-1 in hepatic tissues. Together, these results indicate that chronic l-lactate exposure increases oxidative stress and apoptosis in hepatocytes via upregulation of Bax/Bcl-2 expression and the consequent mitochondrial cytochrome-C release and caspase-3 activation, which contributes to the pathogenesis of hepatic dysfunction.

Effects of Fibroblast Growth Factor 21 on Lactate Uptake and Usage in Mice with Diabetes-Associated Cognitive Decline.

Fibroblast growth factor 21 (FGF21) is an endocrine hormone that exerts beneficial effects on glucose and lipid metabolic homeostasis. However, the impact of FGF21 on type 1 diabetes-associated cognitive decline (DACD) and its mechanisms of action remain unclear. In this study, we aimed to evaluate the effects of FGF21 on lactate uptake and usage in a mouse model of streptozotocin-induced DACD. Six-week-old male C57BL/6 mice were divided into the control, diabetic, and FGF21 (which received 2 mg/kg recombinant human FGF21) groups. At the end of the treatment period, learning and memory performance, nuclear magnetic resonance-based metabonomics, and expressions of various hippocampal protein were analyzed to determine the efficacy of FGF21. The results showed that compared to the control mice, the diabetic mice had reduced long-term memory performance after the hyperglycemic insult; decreased hippocampal levels of lactate dehydrogenase-B (LDH-B) activity, bioenergy metabolites, and monocarboxylate transporter 2 (MCT2); and increased lactate levels. Impaired phosphoinositide 3-kinase (PI3K) signaling was also observed in the diabetic mice. However, FGF21 treatment improved LDH-B activity, ß-nicotinamide adenine dinucleotide, and ATP levels, and increased MCT2 expression and PI3K signaling pathway, which in turn improved the learning and memory defects. These findings demonstrated that the effects of FGF21 on DACD were associated with its ability to improve LDH-B-mediated lactate usage and MCT2-dependent lactate uptake. Further, these beneficial effects of FGF21 in the hippocampus were mediated by the PI3K signaling pathways.