Potential roles of fibroblast growth factor 21 in the brain

BV2 Membrane-Coated PEGylated-Liposomes Delivered hFGF21 to Cortical and Hippocampal Microglia for Alzheimer's Disease Therapy

Microglia-mediated inflammation is involved in the pathogenesis of Alzheimer's disease (AD), whereas human fibroblast growth factor 21 (hFGF21) has demonstrated the ability to regulate microglia activation in Parkinson's disease, indicating a potential therapeutic role in AD. However, challenges such as aggregation, rapid inactivation, and the blood-brain barrier hinder its effectiveness in treating AD. This study develops targeted delivery of hFGF21 to activated microglia using BV2 cell membrane-coated PEGylated liposomes (hFGF21@BCM-LIP), preserving the bioactivity of hFGF21. In vitro, hFGF21@BCM-LIP specifically targets Aβ1-42-induced BV2 cells, with uptake hindered by anti-VCAM-1 antibody, indicating the importance of VCAM-1 and integrin α4/β1 interaction in targeted delivery to BV2 cells. In vivo, following subcutaneous injection near the lymph nodes of the neck, hFGF21@BCM-LIP diffuses into lymph nodes and distributes along the meningeal lymphatic vasculature and brain parenchyma in amyloid-beta (Aβ1-42)-induced mice. Furthermore, the administration of hFGF21@BCM-LIP to activated microglia improves cognitive deficits caused by Aβ1-42 and reduces levels of tau, p-Tau, and BACE1. It also decreases interleukin-6  (IL-6) and tumor necrosis factor-α (TNF-α) release while increasing interleukin-10 (IL-10) release both in vivo and in vitro. These results indicate that hFGF21@BCM-LIP can be a promising treatment for AD, by effectively crossing the blood-brain barrier and targeting delivery to brain microglia via the neck-meningeal lymphatic vasculature-brain parenchyma pathways.

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.

Diagnostic and predictive abilities of myokines in patients with heart failure

Myokines are defined as a heterogenic group of numerous cytokines, peptides and metabolic derivates, which are expressed, synthesized, produced, and released by skeletal myocytes and myocardial cells and exert either auto- and paracrine, or endocrine effects. Previous studies revealed that myokines play a pivotal role in mutual communications between skeletal muscles, myocardium and remote organs, such as brain, vasculature, bone, liver, pancreas, white adipose tissue, gut, and skin. Despite several myokines exert complete divorced biological effects mainly in regulation of skeletal muscle hypertrophy, residential cells differentiation, neovascularization/angiogenesis, vascular integrity, endothelial function, inflammation and apoptosis/necrosis, attenuating ischemia/hypoxia and tissue protection, tumor growth and malignance, for other occasions, their predominant effects affect energy homeostasis, glucose and lipid metabolism, adiposity, muscle training adaptation and food behavior. Last decade had been identified 250 more myokines, which have been investigating for many years further as either biomarkers or targets for heart failure management. However, only few myokines have been allocated to a promising tool for monitoring adverse cardiac remodeling, ischemia/hypoxia-related target-organ dysfunction, microvascular inflammation, sarcopenia/myopathy and prediction for poor clinical outcomes among patients with HF. This we concentrate on some most plausible myokines, such as myostatin, myonectin, brain-derived neurotrophic factor, muslin, fibroblast growth factor 21, irisin, leukemia inhibitory factor, developmental endothelial locus-1, interleukin-6, nerve growth factor and insulin-like growth factor-1, which are suggested to be useful biomarkers for HF development and progression.

Fibroblast growth factor 21 alleviates unilateral ureteral obstruction-induced renal fibrosis by inhibiting Wnt/β-catenin signaling pathway

Fibroblast growth factor 21 (FGF21) is a key regulator of energy metabolism. Recent studies suggested that serum FGF21 levels increase with declining renal function. However, the link between FGF21 and kidney diseases and the direct effect of FGF21 in renal fibrosis remains unclear. In this study, FGF21 was upregulated in unilateral ureteral obstruction (UUO)-induced renal fibrosis and cellular fibrosis induced by transforming growth factor-β, and renal expression of FGF21 was positively correlated with fibrosis markers. Additionally, FGF21 was regulated by Wnt/β-catenin signaling pathway. The knockdown and overexpression of FGF21 in mouse tubular epithelial cells demonstrated that FGF21 alleviates renal fibrosis by inhibiting the Wnt/β-catenin signaling pathway. To investigate the effect of FGF21 on renal fibrosis in vivo, we established an overexpression model by injecting the plasmid in mice and found that FGF21 overexpression relieved UUO-induced renal fibrosis and renal inflammatory response. Taken together, FGF21 is upregulated with the activation of Wnt/β-catenin signaling pathway and alleviates renal fibrosis by inhibiting the activation of Wnt/β-catenin signaling pathway in a negative feedback mode. These results provide a new understanding for the source of elevated serum FGF21 in patients with chronic kidney disease and prove that FGF21 is a direct inhibitor of the progression of renal fibrosis, thus providing novel therapeutic intervention insights for renal fibrosis.

Batokine in Central Nervous System Diseases

Brown adipose tissue (BAT) is a special type of fat tissue in mammals and is also a key endocrine organ in the human body. Batokine, the endocrine effector of BAT, plays a neuroprotective role and improves the prognosis by exerting anti-apoptotic and anti-inflammatory effects, as well as by improving vascular endothelial function and other mechanisms in nerve injury diseases. The present article briefly reviewed several types of batokines related to central nervous system (CNS) diseases. Following this, the potential therapeutic value and future research direction of batokines for CNS diseases were chiefly discussed from the aspects of protective mechanism and signaling pathway.

Defensive responses: behaviour, the brain and the body

Most animals live under constant threat from predators, and predation has been a major selective force in shaping animal behaviour. Nevertheless, defence responses against predatory threats need to be balanced against other adaptive behaviours such as foraging, mating and recovering from infection. This behavioural balance in ethologically relevant contexts requires adequate integration of internal and external signals in a complex interplay between the brain and the body. Despite this complexity, research has often considered defensive behaviour as entirely mediated by the brain processing threat-related information obtained via perception of the external environment. However, accumulating evidence suggests that the endocrine, immune, gastrointestinal and reproductive systems have important roles in modulating behavioural responses to threat. In this Review, we focus on how predatory threat defence responses are shaped by threat imminence and review the circuitry between subcortical brain regions involved in mediating defensive behaviours. Then, we discuss the intersection of peripheral systems involved in internal states related to infection, hunger and mating with the neurocircuits that underlie defence responses against predatory threat. Through this process, we aim to elucidate the interconnections between the brain and body as an integrated network that facilitates appropriate defensive responses to threat and to discuss the implications for future behavioural research.

Glucose-dependent inflammatory responses in obese compared to lean individuals

PURPOSE

Obesity is characterized by chronic inflammation that may contribute to insulin resistance and promote type 2 diabetes. We have investigated whether inflammatory responses to glycemic and insulinemic variations are altered in obese individuals.

METHODS

Eight obese and eight lean individuals without diabetes had undergone hyperinsulinemic-euglycemic-hypoglycemic and hyperglycemic clamps in a previous study. Using Proximity Extension Assay, 92 inflammatory markers were analyzed from plasma samples at fasting, hyperinsulinemia-euglycemia, hypoglycemia and hyperglycemia.

RESULTS

In all participants, hyperinsulinemia, hypoglycemia and hyperglycemia led to reductions of 11, 19 and 62 out of the 70 fully evaluable biomarkers, respectively. FGF-21 increased during both hypoglycemia and hyperglycemia while IL-6 and IL-10 increased during hypoglycemia. In obese vs lean participants, Oncostatin-M, Caspase-8 and 4E-BP1 were more markedly suppressed during hypoglycemia, whereas VEGF-A was more markedly suppressed during hyperglycemia. BMI correlated inversely with changes of PD-L1 and CD40 during hyperinsulinemia, Oncostatin-M, TNFSF14, FGF-21 and 4EBP-1 during hypoglycemia and CCL23, VEGF-A and CDCP1 during hyperglycemia (Rho ≤ -0.50). HbA1c correlated positively with changes of MCP-2 and IL-15-RA during hyperinsulinemia (Rho ≥ 0.51) and inversely with changes of CXCL1, MMP-1 and Axin-1 during hypoglycemia (Rho ≤ -0.55). M-value correlated positively with changes of IL-12B and VEGF-A during hyperglycemia (Rho ≥ 0.51). Results above were significant (p < 0.05).

CONCLUSION

Overall, hyperinsulinemia, hypo- and hyperglycemia led to suppression of several inflammatory markers and this tended to be more marked in individuals with obesity, insulin resistance and dysglycemia. Thus, acute glycemic or insulinemic variations do not seem to potentiate possible inflammatory pathways in the development of insulin resistance and disturbed glucose metabolism.

Hepatokines, bile acids and ketone bodies are novel Hormones regulating energy homeostasis

Current views show that an impaired balance partly explains the fat accumulation leading to obesity. Fetal malnutrition and early exposure to endocrine-disrupting compounds also contribute to obesity and impaired insulin secretion and/or sensitivity. The liver plays a major role in systemic glucose homeostasis through hepatokines secreted by hepatocytes. Hepatokines influence metabolism through autocrine, paracrine, and endocrine signaling and mediate the crosstalk between the liver, non-hepatic target tissues, and the brain. The liver also synthetizes bile acids (BAs) from cholesterol and secretes them into the bile. After food consumption, BAs mediate the digestion and absorption of fat-soluble vitamins and lipids in the duodenum. In recent studies, BAs act not simply as fat emulsifiers but represent endocrine molecules regulating key metabolic pathways. The liver is also the main site of the production of ketone bodies (KBs). In prolonged fasting, the brain utilizes KBs as an alternative to CHO. In the last few years, the ketogenic diet (KD) became a promising dietary intervention. Studies on subjects undergoing KD show that KBs are important mediators of inflammation and oxidative stress. The present review will focus on the role played by hepatokines, BAs, and KBs in obesity, and diabetes prevention and management and analyze the positive effects of BAs, KD, and hepatokine receptor analogs, which might justify their use as new therapeutic approaches for metabolic and aging-related diseases.

The effects of a 20-week exercise program on blood-circulating biomarkers related to brain health in overweight or obese children: The ActiveBrains project

BACKGROUND

Emerging research supports the idea that exercise positively affects neurodevelopment. However, the mechanisms linking exercise with brain health are largely unknown. We aimed to investigate the effect of exercise on (a) blood biomarkers selected based on previous evidence (brain-derived neurotrophic factor, β-hydroxybutyrate (BHB), cathepsin B (CTSB), kynurenine, fibroblast growth factor 21 (FGF21), soluble vascular cell adhesion molecule-1 (sVCAM-1)); and (b) a panel of 92 neurology-related proteins (discovery analysis). We also investigated whether changes in these biomarkers mediate the effects of exercise on brain health (hippocampal structure and function, cognitive performance, and mental health).

METHODS

We randomized 81 overweight/obese children (10.1 ± 1.1 years, 41% girls) into 2 groups: either 20 weeks of aerobic plus resistance exercise or control. Candidate biomarkers were assessed using enzyme-linked immunosorbent assay (ELISA) for kynurenine, FGF21, and CTSB; colorimetry for β-hydroxybutyrate; and XMap for brain-derived neurotrophic factor and soluble vascular cell adhesion molecule-1. The 92 neurology-related proteins were analyzed by an antibody-based proteomic analysis.

RESULTS

Our intervention had no significant effect on candidate biomarkers (all p > 0.05). In the discovery analysis, a reduction in circulating macrophage scavenger receptor type-I was observed (standardized differences between groups = -0.3, p = 0.001). This effect was validated using ELISA methods (standardized difference = -0.3, p = 0.01). None of the biomarkers mediated the effects of exercise on brain health.

CONCLUSIONS

Our study does not support a chronic effect of exercise on candidate biomarkers. We observed that while chronic exercise reduced the levels of macrophage scavenger receptor type-I, it did not mediate the effects of exercise on brain health. Future studies should explore the implications of this novel biomarker for overall health.

Myokines may target accelerated cognitive aging in people with spinal cord injury: A systematic and topical review

Persons with spinal cord injury (SCI) can suffer accelerated cognitive aging, even when correcting for mood and concomitant traumatic brain injury. Studies in healthy older adults have shown that myokines (i.e. factors released from muscle tissue during exercise) may improve brain health and cognitive function. Myokines may target chronic neuroinflammation, which is considered part of the mechanism of cognitive decline both in healthy older adults and SCI. An empty systematic review, registered in PROSPERO (CRD42022335873), was conducted as proof of the lack of current research on this topic in people with SCI. Pubmed, Embase, Cochrane and Web of Science were searched, resulting in 387 articles. None were considered eligible for full text screening. Hence, the effect of myokines on cognitive function following SCI warrants further investigation. An in-depth narrative review on the mechanism of SCI-related cognitive aging and the myokine-cognition link was added to substantiate our hypothetical framework. Readers are fully updated on the potential role of exercise as a treatment strategy against cognitive aging in persons with SCI.

Focus on Alzheimer's Disease: The Role of Fibroblast Growth Factor 21 and Autophagy

Alzheimer's disease (AD) is a disorder of the central nervous system that is typically marked by progressive cognitive impairment and memory loss. Amyloid β plaque deposition and neurofibrillary tangles with hyperphosphorylated tau are the two hallmark pathologies of AD. In mammalian cells, autophagy clears aberrant protein aggregates, thus maintaining proteostasis as well as neuronal health. Autophagy affects production and metabolism of amyloid β and accumulation of phosphorylated tau proteins, whose malfunction can lead to the progression of AD. On the other hand, defective autophagy has been found to induce the production of the neuroprotective factor fibroblast growth factor 21 (FGF21), although the underlying mechanism is unclear. In this review, we highlight the significance of aberrant autophagy in the pathogenesis of AD, discuss the possible mechanisms by which defective autophagy induces FGF21 production, and analyze the potential of FGF21 in the treatment of AD. The findings provide some insights into the potential role of FGF21 and autophagy in the pathogenesis of AD.

Pemafibrate prevents choroidal neovascularization in a mouse model of neovascular age-related macular degeneration

Background

Pathological choroidal neovascularization (CNV) is one of the major causes of visual impairment in neovascular age-related macular degeneration (AMD). CNV has been suppressed by using anti-vascular endothelial growth factor (VEGF) antibodies. However, some clinical cases have demonstrated the failure of anti-VEGF therapies. Furthermore, anti-VEGF agents might induce the development of ocular atrophy. Recently, peroxisome proliferator-activated receptor alpha (PPARα) activation using pemafibrate treatment was suggested as one of the promising therapeutic targets in the prevention of ocular ischemia. However, the preventive role of pemafibrate remains unclear in CNV. We aimed to examine the preventive role of pemafibrate on laser-induced pathological CNV.

Methods

Adult male C57BL/6 mice were orally supplied pemafibrate (0.5 mg/kg) for four days, followed by laser irradiation. Then, pemafibrate was consecutively given to mice with the same condition. CNV was visualized with isolectin-IB4. The eye (retina and/or retinal pigment epithelium [RPE]-choroid), liver, and serum were used for biomolecular analyses.

Results

We found that pemafibrate administration suppressed CNV volumes. Pemafibrate administration activated PPARα downstream genes in the liver and eye (especially, RPE-choroid). Furthermore, pemafibrate administration elevated serum fibroblast growth factor 21 levels and reduced serum levels of triglycerides.

Conclusions

Our data suggest a promising pemafibrate therapy for suppressing CNV in AMD.

Dual Role of Fibroblast Growth Factor Pathways in Sleep Regulation

Sleep plays an important function in neuro-immuno-endocrine homeostasis. Sleep disorders have been associated with an increased risk of metabolic and cognitive impairments. Among different factors that have an effect on sleep metabolism, a growing body of literature has investigated growth factors in the course of sleep quality and disorders. A good example of growth factors is fibroblast growth factors (FGFs), which are a large family of polypeptide growth factors. Evidence has shown that FGFs are involved in the modulation of sleep-wake behavior by their receptor subtypes and ligands, e.g., FFG1 plays an important role in the quality of sleep through somnogenic effects, while the high level of FGF23 is associated with secondary disorders in shift workers. Therefore, a controversial effect of FGFs can be seen in the course of sleep in physiologic and pathologic conditions. Further investigation on this topic would help us to understand the role of FGFs in sleep disorders as a therapeutic option and biomarker.

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, β-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.

FGF21 response to sucrose is associated with BMI and dorsal striatal signaling in humans

OBJECTIVE

This study examined associations between BMI and dietary sugar intake with sucrose-induced fibroblast growth factor 21 (FGF21) and whether circulating FGF21 is associated with brain signaling following sucrose ingestion in humans.

METHODS

A total of 68 adults (29 male; mean [SD), age 23.2 [3.8] years; BMI 27.1 [4.9] kg/m² ) attended visits after a 12-hour fast. Plasma FGF21 was measured at baseline and at 15, 30, and 120 minutes after sucrose ingestion (75 g in 300 mL of water). Brain cerebral blood flow responses to sucrose were measured using arterial spin labeling magnetic resonance imaging.

RESULTS

Higher circulating FGF21 levels were associated with reduced blood flow in the striatum in response to sucrose (β = -7.63, p = 0.03). This association was greatest among persons with healthy weight (β = -15.70, p = 0.007) and was attenuated in people with overweight (β = -4.00, p = 0.63) and obesity (β = -12.45, p = 0.13). BMI was positively associated with FGF21 levels in response to sucrose (β = 0.53, p = 0.02). High versus low dietary sugar intake was associated with greater FGF21 responses to acute sucrose ingestion in individuals with healthy weight (β = 8.51, p = 0.04) but not in individuals with overweight or obesity (p > 0.05).

CONCLUSIONS

These correlative findings support evidence in animals showing that FGF21 acts on the brain to regulate sugar consumption through a negative feedback loop.

An overview of the molecular and physiological antidepressant mechanisms of physical exercise in animal models of depression

BACKGROUND

Depression is a global disease that affects the physical and mental health of people of all ages. Non-pharmacological and unconventional methods of treatment, such as regular physical exercise, have been recommended to treat depression.

METHODS

Here, we briefly review the literature about the physiological and molecular mechanisms of exercise antidepressants in depressive-like behavior in animal models of depression.

RESULTS

The main hysiological and molecular mechanisms of physical exercise in depression include blood flow changes in several areas of the brain, increase in brain serotonin synthesis, increase in antioxidant enzymes, increase in serum and brain brain-derived neuro factor (BDNF) levels, decrease in cortisol levels and reduced inflammation in peripheral and brain tissues. Physical exercise also leads to increased activation of the phosphatidylinositol-3-kinase (PI3K), PGC-1α/FNDC5/Irisin pathway, BDNF concentrations (serum and cerebral), extracellular signal-regulated kinase and cAMP-response element binding protein (mainly in neurons of the hippocampus and prefrontal cortex), which together contribute to fight or inhibit the development of depression symptoms. These molecular and physiological mechanisms work in synchrony, further enhancing their effects.

CONCLUSION

Physical exercise can be used as a safe and effective non-pharmacological treatment in depression.

Bisphenol A reveals its obesogenic effects through disrupting glucose tolerance, oxidant-antioxidant balance, and modulating inflammatory cytokines and fibroblast growth factor in zebrafish

Obesogens affect lipid metabolism, and genetic or epigenetic factors may also contribute to the progression of obesity. Endocrine-disrupting chemicals (EDCs) are the most striking among obesogens. Bisphenol A (BPA) is an estrogenic EDC used in food containers, adhesives, dye powders, and dental fillers. We aimed to elucidate molecular mechanisms of BPA's obesogenic effects focusing on obesogenic pathways in the liver including fibroblast growth factor (FGF) and Dnmt3a which is its epigenetic regulator, oxidant-antioxidant status, and inflammatory cytokines. Zebrafish were divided into three groups as control, low-dose BPA (1 μm BPA), and high-dose BPA groups (10 μm BPA). At the end of 30 days, oral glucose tolerance test (OGTT) was performed, fasting blood glucose levels were measured, and hepatopancreas tissues were taken. Malondialdehyde (MDA) levels, superoxide dismutase (SOD), glutathione S-transferase (GST), and nitric oxide (NO) activities were examined in the hepatopancreas. Inflammatory cytokines, lepa, fgf21, and dnmt3a expressions were determined by RT-PCR. BPA exposure increased the body weights, il1ß, tnfα, il6, lepa, fgf21, and dnmt3a expressions, impaired glucose tolerance, and oxidant-antioxidant status in a dose-dependent manner. Hepatocyte degeneration, lipid vacuolization, and vasocongestion were observed in both BPA-exposed groups. Our study suggests impaired glucose tolerance, oxidant-antioxidant balance, increased inflammatory response, fgf21 expression, and dnmt3a expressions as the possible mechanisms for the BPA-induced obesity model in zebrafish.

Circulating fibroblast growth factor 21 links hemodynamics with kidney function in middle-aged and older adults: A mediation analysis

Altered hemodynamics are commonly observed in individuals with declining renal function; however, the pathophysiological mechanisms linking renal dysfunction and hemodynamics have not been fully elucidated. Fibroblast growth factor 21 (FGF21), which upregulates sympathetic nerve activity, can alter systemic hemodynamics, and its level can increase as renal function declines. This study aimed to determine the associations among circulating FGF21 levels, hemodynamics, and renal function in middle-aged and older adults. In a total of 272 middle-aged and older adults (age range: 46-83 years), estimated glomerular filtration rate (eGFR), hemodynamics (brachial and aortic blood pressure and aortic pulse wave velocity [PWV]), and serum FGF21 levels were measured. For mediation analysis, hemodynamic parameters were entered as outcomes. eGFR or log-transformed urinary albumin and creatinine ratio (UACR) and log-transformed serum FGF21 levels were set as the predictors and mediator, respectively. According to multivariable regression models after adjusting for potential covariates, serum FGF21 levels were significantly associated with brachial systolic blood pressure (β = 0.140), pulse pressure (β = 0.136), and aortic PWV (β = 0.144). Mediation analyses showed that serum FGF21 levels significantly mediated the relationship of eGFR with brachial systolic blood pressure (indirect effect [95% confidence interval]: -0.032 [-0.071, -0.002]), pulse pressure (-0.019 [-0.041, -0.001]), and aortic PWV (-0.457 [-1.053, -0.021]) and the relationship of UACR with aortic PWV (7.600 [0.011, 21.148]). These findings suggest that elevated circulating FGF21 levels partially mediate the association of elevated blood pressure and/or aortic stiffness with renal dysfunction in middle-aged and older adults.

Metabolic determinants of Alzheimer's disease: A focus on thermoregulation

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease, associated with central and peripheral metabolic anomalies, such as impaired glucose utilization and insulin resistance. These observations led to a considerable interest not only in lifestyle-related interventions, but also in repurposing insulin and other anti-diabetic drugs to prevent or treat dementia. Body temperature is the oldest known metabolic readout and mechanisms underlying its maintenance fail in the elderly, when the incidence of AD rises. This raises the possibility that an age-associated thermoregulatory deficit contributes to energy failure underlying AD pathogenesis. Brown adipose tissue (BAT) plays a central role in thermogenesis and maintenance of body temperature. In recent years, the modulation of BAT activity has been increasingly demonstrated to regulate energy expenditure, insulin sensitivity and glucose utilization, which could also provide benefits for AD. Here, we review the evidence linking thermoregulation, BAT and insulin-related metabolic defects with AD, and we propose mechanisms through which correcting thermoregulatory impairments could slow the progression and delay the onset of AD.

Roles of fibroblast growth factor 21 in the control of depression-like behaviours after social defeat stress in male rodents

Fibroblast growth factor 21 (FGF21) modulates energy metabolism and neuroendocrine stress responses. FGF21 synthesis is increased after environmental or metabolic challenges. Detailed roles of FGF21 in the control of behavioural disturbances under stressful conditions remain to be clarified. Here, we examined the roles of FGF21 in the control of behavioural changes after social defeat stress in male rodents. Central administration of FGF21 increased the number of tyrosine hydroxylase-positive catecholaminergic cells expressing c-Fos protein, an activity marker of neurones, in the nucleus tractus solitarius and area postrema. Double in situ hybridisation showed that some catecholaminergic neurones in the dorsal medulla oblongata expressed β-Klotho, an essential co-receptor for FGF21, in male mice. Social defeat stress increased FGF21 concentrations in the plasma of male mice. FGF21-deficient male mice showed social avoidance in a social avoidance test with C57BL/6J mice (background strain of FGF21-deficient mice) and augmented immobility behaviour in a forced swimming test after social defeat stress. On the other hand, overexpression of FGF21 by adeno-associated virus vectors did not significantly change behaviours either in wild-type male mice or FGF21-deficient male mice. The present data are consistent with the view that endogenous FGF21, possibly during the developmental period, has an inhibitory action on stress-induced depression-like behaviour in male rodents.

Liver-specific decrease in Tff3 gene expression in infant mice perinatally exposed to 2,3,7,8-tetrabromodibenzofuran or 2,3,7,8-tetrachlorodibenzo-p-dioxin

Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/DFs) are byproducts of brominated flame retardants and can cause adverse health effects. Although exposure to polychlorinated (PC) DD/DFs induces toxic effects, including liver injury and neurobehavioral disorder, little is known about toxicities associated with PBDD/DF exposure. Thus, we examined effects of perinatal exposure to brominated congener on the infant mouse. Gene expression in several organs, such as the liver and brain, was analyzed in mouse offspring born to dams administered 2,3,7,8-tetrabromodibenzofuran (TBDF; 9 or 45 μg/kg body weight) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 3 μg/kg body weight) on gestational day 12.5. An increase in liver size was observed in TBDF- or TCDD-exposed offspring in infancy. Gene microarray analysis revealed that 163 and 36 genes were markedly upregulated and downregulated, respectively, in the liver of TBDF-exposed mice compared with those in vehicle-treated mice on postnatal day (PND) 5. Significant increases in Cyp1a1, Cyp1a2, Fmo3, and Pnliprp1 and decreases in Tff3, Ocstamp, Kcnk16, and Lgals2 mRNA levels in TBDF-exposed offspring on PNDs 5 and 12 were confirmed by quantitative PCR. In particular, a significant reduction in Tff3 mRNA in the liver, but not in the brain, small intestine, colon, and kidney, was observed in offspring perinatally exposed to TBDF or TCDD. Ultrasonic calls of TBDF- or TCDD-exposed offspring on PNDs 3-5 were impaired. Taken together, perinatal exposure to polyhalogenated dioxin/furan congeners disrupts gene expression patterns in the liver and ultrasonic calling during infancy. These results suggest that liver injury may contribute to neurobehavioral disorder.

Retinal glial remodeling by FGF21 preserves retinal function during photoreceptor degeneration

The group of retinal degenerations, retinitis pigmentosa (RP), comprises more than 150 genetic abnormalities affecting photoreceptors. Finding degenerative pathways common to all genetic abnormalities may allow general treatment such as neuroprotection. Neuroprotection may include enhancing the function of cells that directly support photoreceptors, retinal pigment epithelial cells, and Müller glia. Treatment with fibroblast growth factor 21 (FGF21), a neuroprotectant, from postnatal week 4-10, during rod and cone loss in P23H mice (an RP model) with retinal degeneration, preserved photoreceptor function and normalized Müller glial cell morphology. Single-cell transcriptomics of retinal cells showed that FGF21 receptor Fgfr1 was specifically expressed in Müller glia/astrocytes. Of all retinal cells, FGF21 predominantly affected genes in Müller glia/astrocytes with increased expression of axon development and synapse formation pathway genes. Therefore, enhancing retinal glial axon and synapse formation with neurons may preserve retinal function in RP and may suggest a general therapeutic approach for retinal degenerative diseases.

Neuroprotective Effects of the FGF21 Analogue LY2405319

BACKGROUND

To date, there are no effective treatments for Alzheimer's disease (AD). Thus, a significant need for research of therapies remains.

OBJECTIVE

One promising pharmacological target is the hormone fibroblast growth factor 21 (FGF21), which is thought to be neuroprotective. A clinical candidate for medical use could be the FGF21 analogue LY2405319 (LY), which has a specificity and potency comparable to FGF21.

METHODS

The present study investigated the potential neuroprotective effect of LY via PPARγ/apoE/abca1 pathway, which is known to degrade amyloid-β (Aβ) plaques by using primary glial cells and hippocampal organotypic brain slice cultures (OBSCs) from 30- and 50-week-old transgenic APPswe/PS1dE9 (tg) mice. By LY treatment of 52-week-old tg mice with advanced Aβ deposition, we further aimed to elaborate the effect of LY on AD pathology in vivo.

RESULTS

LY application to primary glial cells caused an upregulation of pparγ, apoE, and abca1 mRNA expression and significantly decreased number and area of Aβ plaques in OBSCs. LY treatment in tg mice increased cerebral [18F] FDG uptake and N-acetylaspartate/creatine ratio indicating enhanced neuronal activity and integrity. Although LY did not reduce the number of Aβ plaques in tg mice, the number of iba1-positive cells was significantly decreased indicating reduced microgliosis.

CONCLUSION

These data identified LY in vitro as an activator of Aβ degrading genes leading to cerebral Aβ load amelioration in early and late AD pathology. Although Aβ plaque reduction by LY failed in vivo, LY may be used as therapeutic agent to treat AD-related neuroinflammation and impaired neuronal integrity.

Potential therapeutic role of fibroblast growth factor 21 in neurodegeneration: Evidence for ameliorating parkinsonism via silent information regulator 2 homolog 1 and implication for gene therapy

Parkinson's disease (PD) is one of the common complex neurodegenerative diseases and characterized by abnormal metabolic brain networks. Fibroblast growth factor 21 (FGF21), an endocrine hormone that belongs to the fibroblast growth factor superfamily, plays an extensive role in the regulation of metabolism. However, our understandings of the specific function and mechanisms of FGF21 on PD are still quite limited. Here we aimed to elucidate the actions and the underlying mechanisms of FGF21 on dopaminergic neurodegeneration using cellular and animal models of parkinsonism. To investigate the effects of FGF21 on dopaminergic neurodegeneration in vivo and in vitro, 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine models of PD were utilized, and animals were treated with recombinant FGF21 protein or FGF21 gene delivered via an adeno-associated virus. In the present study, systemic and continuous intracerebroventricular recombinant FGF21 protein administration to mice both prevented behavioral deficits, protected dopaminergic neurons against degeneration, and ameliorated α-synuclein pathology in PD models; and in vivo gene delivery of FGF21 improved PD-like symptoms and pathologies suggesting a potential implication of FGF21 in gene therapy for PD. In vitro evidence confirmed FGF21 mediated neuroprotective benefits against PD pathologies. Further, our data suggested that enhanced autophagy was involved in the FGF21 neuroprotection in PD models, and silent information regulator 2 homolog 1 may play a crucial role in molecular mechanisms underlying anti-PD activities of FGF21.

Pemafibrate Protects Against Retinal Dysfunction in a Murine Model of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the leading causes of blindness globally. Retinal neuronal abnormalities occur in the early stage in DR. Therefore, maintaining retinal neuronal activity in DR may prevent vision loss. Previously, pemafibrate, a novel selective peroxisome proliferator-activated receptor alpha modulator, was suggested as a promising drug in hypertriglyceridemia. However, the role of pemafibrate remains obscure in DR. Therefore, we aimed to unravel systemic and retinal changes by pemafibrate in diabetes. Adult mice were intraperitoneally injected with streptozotocin (STZ) to induce diabetes. After STZ injection, diet supplemented with pemafibrate was given to STZ-induced diabetic mice for 12 weeks. During the experiment period, body weight and blood glucose levels were examined. Electroretinography was performed to check the retinal neural function. After sacrifice, the retina, liver, and blood samples were subjected to molecular analyses. We found pemafibrate mildly improved blood glucose level as well as lipid metabolism, boosted liver function, increased serum fibroblast growth factor21 level, restored retinal functional deficits, and increased retinal synaptophysin protein expression in STZ-induced diabetic mice. Our present data suggest a promising pemafibrate therapy for the prevention of early DR by improving systemic metabolism and protecting retinal function.

Metformin Therapy Aggravates Neurodegenerative Processes in ApoE-/- Mice

Epidemiological studies suggest that individuals with diabetes mellitus are at greater risk of developing Alzheimer's disease. A well-known insulin-sensitizing drug and the most widely prescribed oral medication for diabetes is metformin. There is evidence that metformin acts in a neuroprotective manner via the AMPK/mTOR pathway by inhibiting the tau phosphorylation. In addition, it is known that metformin upregulates Fgf21, which in turn activates the AMPK/mTOR pathway and mediates neuroprotection. Thus, metformin-induced Fgf21 release may be involved in AMPK/mTOR activation. However, some studies reported that metformin causes cognition impairment. Due to the controversial data on the neuroprotective properties of metformin, we treated Apolipoprotein E deficient (ApoE- /-) mice, a mouse model of tauopathy, with metformin for 18 weeks. Metformin-treated mice revealed increased expression of lipogenic genes, i.e., lxrα and srebp1c. In line with this, metformin caused an increase in plasma triglyceride leading to enhanced gliosis as indicated by an increase of GFAP-positive cells. Although the systemic Fgf21 concentration was increased, metformin did not activate the FgfR1c/AMPK/mTOR pathway suggesting a Fgf21-resistant state. Further, metformin-treated mice showed increased tau phosphorylation and reduced numbers of NeuN-and PSD95-positive cells. Thus, metformin-associated lipogenesis as well as inflammation aggravated neurodegenerative processes in ApoE- /- mice. Consequently, this study supports previous observations showing that metformin causes impairment of cognition.

FGF21 Protects against Aggravated Blood-Brain Barrier Disruption after Ischemic Focal Stroke in Diabetic db/db Male Mice via Cerebrovascular PPARγ Activation

Recombinant fibroblast growth factor 21 (rFGF21) has been shown to be potently beneficial for improving long-term neurological outcomes in type 2 diabetes mellitus (T2DM) stroke mice. Here, we tested the hypothesis that rFGF21 protects against poststroke blood–brain barrier (BBB) damage in T2DM mice via peroxisome proliferator-activated receptor gamma (PPARγ) activation in cerebral microvascular endothelium. We used the distal middle cerebral occlusion (dMCAO) model in T2DM mice as well as cultured human brain microvascular endothelial cells (HBMECs) subjected to hyperglycemic and inflammatory injury in the current study. We detected a significant reduction in PPARγ DNA-binding activity in the brain tissue and mRNA levels of BBB junctional proteins and PPARγ-targeting gene CD36 and FABP4 in cerebral microvasculature at 24 h after stroke. Ischemic stroke induced a massive BBB leakage two days after stroke in T2DM mice compared to in their lean controls. Importantly, all abnormal changes were significantly prevented by rFGF21 administration initiated at 6 h after stroke. Our in vitro experimental results also demonstrated that rFGF21 protects against hyperglycemia plus interleukin (IL)-1β-induced transendothelial permeability through upregulation of junction protein expression in an FGFR1 activation and PPARγ activity elevation-dependent manner. Our data suggested that rFGF21 has strong protective effects on acute BBB leakage after diabetic stroke, which is partially mediated by increasing PPARγ DNA-binding activity and mRNA expression of BBB junctional complex proteins. Together with our previous investigations, rFGF21 might be a promising candidate for treating diabetic stroke.

Endocrine Regulator rFGF21 (Recombinant Human Fibroblast Growth Factor 21) Improves Neurological Outcomes Following Focal Ischemic Stroke of Type 2 Diabetes Mellitus Male Mice

Background and Purpose- The complexity and heterogeneity of stroke, as well as the associated comorbidities, may render neuroprotective drugs less efficacious in clinical practice. Therefore, the development of targeted therapies to specific patient subsets has become a high priority in translational stroke research. Ischemic stroke with type 2 diabetes mellitus has a nearly double mortality rate and worse neurological outcomes. In the present study, we tested our hypothesis that rFGF21 (recombinant human fibroblast growth factor 21) administration is beneficial for improving neurological outcomes of ischemic stroke with type 2 diabetes mellitus. Methods- Type 2 diabetes mellitus db/db and nondiabetic genetic control db/+ mice were subjected into permanent focal ischemia of distal middle cerebral artery occlusion, we examined the effects of poststroke administration with rFGF21 in systemic metabolic disorders, inflammatory gatekeeper PPARγ (peroxisome proliferator-activated receptor γ) activity at 3 days, mRNA expression of inflammatory cytokines and microglia/macrophage activation at 7 days in the perilesion cortex, and last neurological function deficits, ischemic brain infarction, and white matter integrity up to 14 days after stroke of db/db mice. Results- After permanent focal ischemia, diabetic db/db mice presented confounding pathological features, including metabolic dysregulation, more severe brain damage, and neurological impairment, especially aggravated proinflammatory response and white matter integrity loss. However, daily rFGF21 treatment initiated at 6 hours after stroke for 14 days significantly normalized systemic metabolic disorders, rescued PPARγ activity decline, inhibited proinflammatory cytokine mRNA expression, and M1-like microglia/macrophage activation in the brain. Importantly, rFGF21 also significantly reduced white matter integrity loss, ischemic brain infarction, and neurological function deficits up to 14 days after stroke. The potential mechanisms of rFGF21 may in part consist of potent systematic metabolic regulation and PPARγ-activation promotion-associated antiproinflammatory roles in the brain. Conclusions- Taken together, these results suggest rFGF21 might be a novel and potent candidate of the disease-modifying strategy for treating ischemic stroke with type 2 diabetes mellitus.

Tanycytes Regulate Lipid Homeostasis by Sensing Free Fatty Acids and Signaling to Key Hypothalamic Neuronal Populations via FGF21 Secretion

The hypothalamus plays a key role in the detection of energy substrates to regulate energy homeostasis. Tanycytes, the hypothalamic ependymo-glia, are located at a privileged position to integrate multiple peripheral inputs. We observed that tanycytes produce and secrete Fgf21 and are located close to Fgf21-sensitive neurons. Fasting, likely via the increase in circulating fatty acids, regulates this central Fgf21 production. Tanycytes store palmitate in lipid droplets and oxidize it, leading to the activation of a reactive oxygen species (ROS)/p38-MAPK signaling pathway, which is essential for tanycytic Fgf21 expression upon palmitate exposure. Tanycytic Fgf21 deletion triggers an increase in lipolysis, likely due to impaired inhibition of key neurons during fasting. Mice deleted for tanycytic Fgf21 exhibit increased energy expenditure and a reduction in fat mass gain, reminiscent of a browning phenotype. Our results suggest that tanycytes sense free fatty acids to maintain body lipid homeostasis through Fgf21 signaling within the hypothalamus.

Organokines in disease

Studies have linked obesity, metabolic syndrome, type 2 diabetes, cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD) and dementia. Their relationship to the incidence and progression of these disease states suggests an interconnected pathogenesis involving chronic low-grade inflammation and oxidative stress. Metabolic syndrome represents comorbidities of central obesity, insulin resistance, dyslipidemia, hypertension and hyperglycemia associated with increased risk of type 2 diabetes, NAFLD, atherosclerotic CVD and neurodegenerative disease. As the socioeconomic burden for these diseases has grown signficantly with an increasing elderly population, new and alternative pharmacologic solutions for these cardiometabolic diseases are required. Adipose tissue, skeletal muscle and liver are central endocrine organs that regulate inflammation, energy and metabolic homeostasis, and the neuroendocrine axis through synthesis and secretion of adipokines, myokines, and hepatokines, respectively. These organokines affect each other and communicate through various endocrine, paracrine and autocrine pathways. The ultimate goal of this review is to provide a comprehensive understanding of organ crosstalk. This will include the roles of novel organokines in normal physiologic regulation and their pathophysiological effect in obesity, metabolic syndrome, type 2 diabetes, CVD, NAFLD and neurodegenerative disorders.

Effect of catalpol on behavior and neurodevelopment in an ADHD rat model

Studies suggest that abnormal neurodevelopment of prefrontal striatal circuits is implicated in the pathogenesis of attention deficit hyperactivity disorder (ADHD). In the present study, we investigated the effect of catalpol, an active ingredient of Rehmanniae radix preparata, which is the most frequently used Chinese medicinal herb for the treatment of ADHD, on behavior and neurodevelopment in spontaneously hypertensive rats (SHR). SHR were divided into SHR group (vehicle, i.g.), methylphenidate (MPH) group (2 mg/kg/day, i.g.), and catalpol group (50 mg/kg/day i.g.), and Wistar-Kyoto (WKY) rats were used as control group (vehicle, i.g.). Open Field Test (OFT) and Morris water maze (MWM) test were performed to assess the effect of catalpol on behavior. Results revealed that both catalpol and MPH treatment decreased average speed, time spent in the central area, rearing times, and central area visits, increased the immobility time of SHR in OFT, and increased number of visits to the annulus, and time spent in target quadrant in the MWM test. Hematoxylin and eosin (H&E) staining showed that catalpol reduced irregular neuronal arrangement, ruptured nuclear membranes, and resulted in disappearance of the nucleolus in the prefrontal cortex (PFC) and striatum of SHR. Moreover, immuno-fluorescent staining of NeuN and myelin basic protein (MBP) indicated that catalpol ameliorated neuronal loss and contributed to myelination. Finally, western blot and immunostaining analysis suggested that several regulatory proteins involved in PFC development were up-regulated by catalpol treatment, such as brain-derived neurotrophic factor (BDNF), cyclin-dependent kinase 5 (Cdk5), p35, fibroblast growth factor (FGF) 21 and its receptor (FGFR)1. Taken together, catalpol can effectively ameliorate hyperactive and impulsive behavior, improve spatial learning and memory in SHR, likely through the neurodevelopmental pathways. Nonetheless, whether catalpol could attenuate inattention in SHR and the pathway by which catalpol reduces neuronal loss remain to be further studied.

FGF21 promotes functional recovery after hypoxic-ischemic brain injury in neonatal rats by activating the PI3K/Akt signaling pathway via FGFR1/β-klotho

Perinatal asphyxia often results in neonatal cerebral hypoxia-ischemia (HI), which is associated with high mortality and severe long-term neurological deficits in newborns. Currently, there are no effective drugs to mitigate the functional impairments post-HI. Previous studies have shown that fibroblast growth factor 21 (FGF21) has a potential neuroprotective effect against brain injury. However, the effect of FGF21 on neonatal HI brain injury is unclear. In the present study, both in vivo and in vitro models were used to assess whether recombinant human FGF21 (rhFGF21) could exert a neuroprotective effect after HI and explore the associated mechanism. The results showed that the rhFGF21 treatment remarkably reduced the infarct volume, ameliorated the body weight and improved the tissue structure after HI in neonatal rats. In addition, the rhFGF21 treatment lengthened the running endurance times in the rotarod test and decreased the mean escape latencies and increased the number of platform crossings in the Morris water maze test at 21 d post-HI insult. In contrast, the FGFR1 inhibitor PD173074 and PI3K inhibitor LY294002 partially reversed these therapeutic effects. In isolated primary cortical neurons, the rhFGF21 treatment protected primary neurons from oxygen-glucose deprivation (OGD) insult by inhibiting neuronal apoptosis and promoting neuronal survival. Both our in vivo and in vitro results reveal that rhFGF21 could inhibit neuronal apoptosis by activating the PI3K/Akt signaling pathway via FGF21/FGFR1/β-klotho complex formation. Therefore, rhFGF21 may be a promising therapeutic agent for promoting functional recovery after HI-induced neonatal brain injury.

High serum levels of FGF21 are decreased in bipolar mania patients during psychotropic medication treatment and are associated with increased metabolism disturbance

Bipolar disorder (BD), a psychiatric illness, results partly as a side effect of psychotropic medications and presents a high risk of metabolic disturbance. Fibroblast growth factor 21 (FGF21) is as an important regulator in carbohydrate and lipid metabolism. In this study, we investigated the serum levels of FGF21 and analyzed its association with metabolic parameters in bipolar mania patients at pre- and post-treatment with psychotropic medications. Bipolar mania inpatients (n = 99) and healthy controls (n = 99) were included at baseline; the patients were followed up after four-week treatment. Serum levels of FGF21 and several metabolic parameters were measured by appropriate detection methods. We found that baseline serum FGF21 levels were significantly higher in bipolar manic patients when compared to that in controls. After four-week medication, FGF21 levels were found to be decreased in patients when compared to the baseline suggesting that FGF21 may be associated with the psychopathology of bipolar mania. Moreover, FGF21 levels were found to be negatively correlated with the serum triglycerides (TG), cholesterol (CHO), low-density lipoprotein cholesterol (LDL-C), apolipoprotein B (Apo B), glucose (Glu), and Body Mass Index (BMI). In addition, our data also indicates that FGF21 may monitor and/or prevent the metabolic abnormalities induced by psychotropic drugs.

Fibroblast growth factor 21 ameliorates neurodegeneration in rat and cellular models of Alzheimer's disease

Our understanding of the mechanisms underlying process in Alzheimer's disease (AD) is far from completion and new therapeutic targets are urgently needed. Recently, the link between dementia and diabetes mellitus (DM) prompted us to search for new therapeutic strategies from glucose metabolism regulators for neurodegeneration. Previous studies have indicated that fibroblast growth factor 21 (FGF21), an attractive and potential therapeutic treatment for DM, may exert diverse effects in the central nervous system. However, the specific biological function and mechanisms of FGF21 on AD is still largely unknown. We report here a study in vivo and in vitro of the neuroprotective effects of FGF21 on cell apoptosis, tau hyperphosphorylation and oxidative stress induced by amyloid β-peptide 25–35. In the present study, the results also further provided evidence for molecular mechanisms by which FGF21 exerted its beneficial effects in neuron and suggested that the regulation of protein phosphatase 2A / mitogen-activated protein kinases / hypoxia-inducible factor-1α pathway may play a key role in mediating the neuroprotective effects of FGF21 against AD-like pathologies.

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In vivo and in vitro evidence for Aβ -induced neurodegeneration ameliorated by FGF21.

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FGF21 alleviated tau and oxidative stress pathologies in AD rat and cellular models.

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PP2A / MAPKs / HIF-1α pathway was involved in the neuroprotective effect of FGF21.

Effects of central FGF21 infusion on the hypothalamus-pituitary-thyroid axis and energy metabolism in rats

The aim of this study was to evaluate the impact of intracerebroventricular chronic fibroblast growth factor 21 (FGF21) infusion on hypothalamic-pituitary-thyroid (HPT) axis, energy metabolism, food intake and body weight. Thirty male Wistar albino rats were used and divided into three groups including control, sham (vehicle) and FGF21 infused groups (n = 10). Intracerebroventricularly, FGF21 and vehicle groups were infused for 7 days with FGF21 (0.72 µg/day) and artificial cerebrospinal fluid, respectively. During the experimental period, changes in food intake and body weight were recorded daily. Serum thyroid stimulating hormone (TSH), Triiodothyronine (T3) and thyroxine (T4) levels were measured using ELISA. TRH and uncoupling protein 1 (UCP1) gene expressions were analyzed by using RT-PCR in hypothalamus and adipose tissues, respectively. Chronic infusion of FGF21 significantly increased serum TSH (p < 0.05), T3 (p < 0.05) and T4 (p < 0.001) levels. Additionally, hypothalamic TRH (p < 0.05) and UCP1 gene expressions (p < 0.05) in white adipose tissue were found to be higher than in the vehicle and control groups. While FGF21 infusion did not cause a significant change in food consumption, it caused a reduction in the body weight of rats (p < 0.05). Our findings indicate that FGF21 may have an effect on energy metabolism via the HPT axis.

FGF21 Protects the Blood-Brain Barrier by Upregulating PPARγ via FGFR1/β-klotho after Traumatic Brain Injury

Blood-brain barrier (BBB) disruption and dysfunction result in brain edema, which is responsible for more than half of all deaths after severe traumatic brain injury (TBI). Fibroblast growth factor 21 (FGF21) has a potential neuroprotective function in the brain. However, the effects and underlying possible mechanism of action on BBB integrity following TBI remain unknown. The purpose of the current study was to determine the effects of FGF21 on BBB protection and TBI treatment. The effects of recombinant human FGF21 (rhFGF21) on BBB integrity and on tight junction (TJ) and adhesion junction (AJ) proteins were investigated both in a TBI mouse model and an in vitro BBB disruption model established with tumor necrosis factor alpha (TNF-α)-induced human brain microvascular endothelial cells (HBMECs). The ability of rhFGF21 to form an FGF21/FGFR1/β-klotho complex was confirmed by in vitro β-klotho small interfering RNA (siRNA) transfection and FGFR1 co-immunoprecipitation. In addition, the specific FGFR1 and peroxisome proliferator-activated receptor gamma (PPARγ) inhibitors PD173074 and GW9662, respectively, were applied to further explore the possible mechanism of rhFGF21 in BBB maintenance after TBI. rhFGF21 markedly reduced neurofunctional behavior deficits and cerebral edema degree, preserved BBB integrity, and recued brain tissue loss and neuron apoptosis in the mouse model after TBI. Both in vivo and in vitro, rhFGF21 upregulated TJ and AJ proteins, thereby preserving the BBB. Moreover, rhFGF21 activated PPARγ in TNF-α-induced HBMECs through formation of an FGF21/FGFR1/β-klotho complex. rhFGF21 protected the BBB through FGF21/FGFR1/β-klotho complex formation and PPARγ activation, which upregulated TJ and AJ proteins.

FGF 21 deficiency slows gastric emptying and reduces initial blood alcohol concentration in mice exposed to acute alcohol in fasting state

Excess alcohol consumption can lead to alcoholic liver disease. Fibroblast growth factor 21 (FGF21) is a metabolic regulator with multiple physiologic functions. Previous study demonstrated that FGF21 deficiency exacerbated alcohol-induced liver injury and exogenous FGF21 administration protected liver from chronic alcohol-induced injury. In this study, we aimed to explore the role of FGF21 in alcohol metabolism in mice. FGF21 knockout (KO) mice and the wild type(WT) control mice were divided into two groups and fasted for 24 h followed by a bonus of alcohol treatment at a dose of 5 g/kg body weight via gavage. Serum alcohol concentration was measured after gavage at 0.5, 2, 3, 4 and 6 h, respectively. At the end, gastric and liver tissues were collected. Serum alcohol concentration of KO mice was significantly lower than that of WT at 0.5 h after alcohol expose. There were no significant differences in alcohol dehydrogenase (ADH) activity and aldehyde dehydrogenase 2 (ALDH2) activity in gastric and liver tissues between WT and the KO mice. However, gastric emptying time of KO mice was much longer than that of WT mice. In addition, the intestinal permeability and serum GLP-1 level of KO mice were significantly higher than that of WT mice. These results suggest that FGF21 deficiency slow gastric emptying rate and indirectly influence initial alcohol metabolism in mice exposed to acute alcohol. Our findings provide additional information for understanding the gastrointestinal mechanism of alcoholic liver disease and other alcohol use disorders.

Long-term caloric restriction in ApoE-deficient mice results in neuroprotection via Fgf21-induced AMPK/mTOR pathway

Caloric restriction (CR) decelerates the aging process, extends lifespan and exerts neuroprotective effects in diverse species by so far unknown mechanisms. Based on known neuroprotective effects of fibroblastic growth factor 21 (Fgf21) we speculate that CR upregulates Fgf21, which phosphorylates neuronal AMP-activated protein kinase (AMPK), leading to a decrease of mammalian target of rapamycin (mTOR) signaling activity and an inhibition of tau-hyperphosphorylation. This in turn reduces the formation of neurofibrillary tangles, a neuropathological hallmark of Alzheimer's disease. ApoE-deficient mice (ApoE−/−), serving as a model of neurodegeneration, showed upon CR vs. ad libitum feeding increased Fgf21 levels in both, plasma and brain as well as higher phosphorylation of fibroblastic growth factor receptor 1c (Fgfr1c), extracellular signal-regulated kinases 1/2 (ERK1/2) and AMPK in brain, lower activity of mTOR and decreased Tau-phosphorylation. Finally, CR in ApoE−/− mice caused neuroprotection as indicated by a higher synaptic plasticity shown by immunohistochemical analysis with increased numbers of PSD95-positive neurons and a better cognitive performance as analyzed with Morris water maze test. These data provide substantial evidence that neuroprotection upon CR seems to be Fgf21-dependent. Further experiments are necessary to evaluate Fgf21 as a therapeutic tool to treat tauopathy for improvement of cognitive performance.

Regulation of longevity by FGF21: Interaction between energy metabolism and stress responses

Fibroblast growth factor 21 (FGF21) is a hormone-like member of FGF family which controls metabolic multiorgan crosstalk enhancing energy expenditure through glucose and lipid metabolism. In addition, FGF21 acts as a stress hormone induced by endoplasmic reticulum stress and dysfunctions of mitochondria and autophagy in several tissues. FGF21 also controls stress responses and metabolism by modulating the functions of somatotropic axis and hypothalamic-pituitary-adrenal (HPA) pathway. FGF21 is a potent longevity factor coordinating interactions between energy metabolism and stress responses. Recent studies have revealed that FGF21 treatment can alleviate many age-related metabolic disorders, e.g. atherosclerosis, obesity, type 2 diabetes, and some cardiovascular diseases. In addition, transgenic mice overexpressing FGF21 have an extended lifespan. However, chronic metabolic and stress-related disorders involving inflammatory responses can provoke FGF21 resistance and thus disturb healthy aging process. First, we will describe the role of FGF21 in interorgan energy metabolism and explain how its functions as a stress hormone can improve healthspan. Next, we will examine both the induction of FGF21 expression via the integrated stress response and the molecular mechanism through which FGF21 enhances healthy aging. Finally, we postulate that FGF21 resistance, similarly to insulin resistance, jeopardizes human healthspan and accelerates the aging process.

FGF21 Attenuates High-Fat Diet-Induced Cognitive Impairment via Metabolic Regulation and Anti-inflammation of Obese Mice

Accumulating studies suggest that overnutrition-associated obesity may lead to development of type 2 diabetes mellitus and metabolic syndromes (MetS). MetS and its components are important risk factors of mild cognitive impairment, age-related cognitive decline, vascular dementia, and Alzheimer's disease. It has been recently proposed that development of a disease-course modification strategy toward early and effective risk factor management would be clinically significant in reducing the risk of metabolic disorder-initiated cognitive decline. In the present study, we propose that fibroblast growth factor 21 (FGF21) is a novel candidate for the disease-course modification approach. Using a high-fat diet (HFD) consumption-induced obese mouse model, we tested our hypothesis that recombinant human FGF21 (rFGF21) administration is effective for improving obesity-induced cognitive dysfunction and anxiety-like behavior, by its multiple metabolic modulation and anti-pro-inflammation actions. Our experimental findings support our hypothesis that rFGF21 is protective to HFD-induced cognitive impairment, at least in part by metabolic regulation in glucose tolerance impairment, insulin resistance, and hyperlipidemia; potent systemic pro-inflammation inhibition; and improvement of hippocampal dysfunction, particularly by inhibiting pro-neuroinflammation and neurogenesis deficit. This study suggests that FGF21 might be a novel molecular target of the disease-course-modifying strategy for early intervention of MstS-associated cognitive decline.

Fibroblast growth factor 21, assisted by elevated glucose, activates paraventricular nucleus NUCB2/Nesfatin-1 neurons to produce satiety under fed states

Fibroblast growth factor 21 (FGF21), liver-derived hormone, exerts diverse metabolic effects, being considered for clinical application to treat obesity and diabetes. However, its anorexigenic effect is debatable and whether it involves the central mechanism remains unclarified. Moreover, the neuron mediating FGF21’s anorexigenic effect and the systemic energy state supporting it are unclear. We explored the target neuron and fed/fasted state dependence of FGF21’s anorexigenic action. Intracerebroventricular (ICV) injection of FGF21 markedly suppressed food intake in fed mice with elevated blood glucose. FGF21 induced c-Fos expression preferentially in hypothalamic paraventricular nucleus (PVN), and increased mRNA expression selectively for nucleobindin 2/nesfatin-1 (NUCB2/Nesf-1). FGF21 at elevated glucose increased [Ca²⁺]_i in PVN NUCB2/Nesf-1 neurons. FGF21 failed to suppress food intake in PVN-preferential Sim1-Nucb2-KO mice. These findings reveal that FGF21, assisted by elevated glucose, activates PVN NUCB2/Nesf-1 neurons to suppress feeding under fed states, serving as the glycemia-monitoring messenger of liver-hypothalamic network for integrative regulation of energy and glucose metabolism.

FGF21 activates AMPK signaling: impact on metabolic regulation and the aging process

Fibroblast growth factor 21 (FGF21) has a significant role in the regulation of energy metabolism, e.g., in the control of systemic glucose and lipid metabolism. For instance, FGF21 enhances insulin sensitivity, increases glucose uptake, and thus can decrease serum hyperglycemia, while it also increases lipid oxidation and inhibits lipogenesis. AMP-activated protein kinase (AMPK) is a tissue energy sensor involved in maintaining the energy balance and tissue integrity. It is known that AMPK signaling generates an energy metabolic profile which displays a remarkable overlap with that of FGF21. There is convincing evidence that endocrine FGF21 signaling activates the AMPK pathway, either directly through FGFR1/β-klotho signaling or indirectly by stimulating the secretion of adiponectin and corticosteroids, which consequently can activate AMPK signaling in their target tissues. By activating AMPK, FGF21 can promote a healthy aging process and thus extend mammalian lifespan. We will examine the signaling mechanisms through which FGF21 can activate the AMPK pathway and then discuss the significance of the close connection between FGF21 and AMPK signaling in the control of metabolic disorders and the aging process.

Roux-en-Y gastric bypass surgery is effective in fibroblast growth factor-21 deficient mice

Objective

The mechanisms by which bariatric surgeries so effectively and lastingly reduce body weight and normalize metabolic dysfunction are not well understood. Fibroblast growth fator-21 (FGF21) is a key regulator of metabolism and is currently considered for treatment of obesity. Although elevated by acute food deprivation, it is downregulated after weight loss induced by chronic calorie restriction but not after Roux-en-Y gastric bypass surgery. Therefore, the goal of the present study was to assess the role of FGF21-signaling in the beneficial effects of Roux-en-Y gastric bypass surgery (RYGB).

Methods

High-fat diet-induced obese FGF21-deficient (FGF21^−/−) and wildtype (WT) mice were subjected to RYGB, sham surgery, or caloric restriction to match body weight of RYGB mice. Body weight, body composition, food intake, energy expenditure, glucose tolerance, and insulin sensitivity, as well as plasma levels and hepatic mRNA expression of FGF21 were measured.

Results

Hepatic expression and plasma levels of FGF21 are higher after RYGB compared with similar weight loss induced by caloric restriction, suggesting that elevated FGF21 might play a role in preventing increased hunger and weight regain after RYGB. However, although the body weight differential between RYGB and sham surgery was significantly reduced in FGF21^−/− mice, RYGB induced similarly sustained body weight and fat mass loss, initial reduction of food intake, increased energy expenditure, and improvements in glycemic control in FGF21^−/− and WT mice.

Conclusions

FGF21 signaling is not a critical single factor for the beneficial metabolic effects of RYGB. This may open up the possibility to use FGF21 as adjuvant therapy in patients with ineffective bariatric surgeries.

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FGF21 plasma levels are higher after RYGB compared to the same weight loss induced by caloric restriction.

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FGF21-signaling might thus play a role in the beneficial effects of RYGB.

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Contrary to expectations, RYGB lowers body weight, fat mass, and food intake similarly in FGF21^−/− and wildtype mice.

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RYGB improves glycemic control similarly in FF21-deficient and wildtype mice in a largely weight loss-dependent fashion.

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FGF21 is potentially useful as adjuvant therapy in unsuccessful bariatric surgery cases.