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

Fibroblast growth factor 21 alleviates diabetes-induced cognitive decline

Diabetes mellitus (DM) causes damage to the central nervous system, resulting in cognitive impairment. Fibroblast growth factor 21 (FGF21) exhibits the potential to alleviate neurodegeneration. However, the therapeutic effect of intracerebroventricular (i.c.v) FGF21 infusion on diabetes-induced cognitive decline (DICD) and its potential mechanisms remain unclear. In this study, the impact of FGF21 on DICD was explored, and 1H nuclear magnetic resonance (NMR)-based metabolomics plus 13C NMR spectroscopy in combine with intravenous [1-13C]-glucose infusion were used to investigate the underlying metabolic mechanism. Results revealed that i.c.v FGF21 infusion effectively improved learning and memory performance of DICD mice; neuron loss and apoptosis in hippocampus and cortex were significantly blocked, suggesting a potential neuroprotective role of FGF21 in DICD. Metabolomics results revealed that FGF21 modulated DICD metabolic alterations related to glucose and neurotransmitter metabolism, which are characterized by distinct recovered enrichment of [3-13C]-lactate, [3-13C]-aspartate, [4-13C]-glutamine, [3-13C]-glutamine, [4-13C]-glutamate, and [4-13C]- γ-aminobutyric acid (GABA) from [1-13C]-glucose. Moreover, diabetes-induced neuron injury and metabolic dysfunctions might be mediated by PI3K/AKT/GSK-3β signaling pathway inactivation in the hippocampus and cortex, which were activated by i.c.v injection of FGF21. These findings indicate that i.c.v FGF21 infusion exerts its neuroprotective effect on DICD by remodeling cerebral glucose and neurotransmitter metabolism by activating the PI3K/AKT/GSK-3β signaling pathway.

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.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

Astrocytes as metabolic suppliers to support neuronal activity and brain functions

Energy metabolism is essential for brain function. In recent years, lactate shuttling between astrocytes and neurons has become a fundamental concept of neuroenergetics. However, it remains unclear to what extent this process is critical for different aspects of cognition, their underlying mechanisms, as well as for the signals used to monitor brain activation.