Increased innervation of forebrain targets by midbrain dopaminergic neurons in the absence of FGF-2

A dual-omics approach on the effects of fibroblast growth factor-2 (FGF-2) on ventral tegmental area dopaminergic neurons in response to alcohol consumption in mice

Harmful alcohol consumption is a major socioeconomic burden to the health system, as it can be the cause of mortality of heavy alcohol drinkers. The dopaminergic (DAergic) system is thought to play an important role in the pathogenesis of alcohol drinking behaviour; however, its exact role remains elusive. Fibroblast growth factor 2 (FGF-2), a neurotrophic factor, associated with both the DAergic system and alcohol consumption, may play an important role in DAergic neuroadaptations during alcohol abuse. Within this study, we aimed to clarify the role of endogenous FGF-2 on the DAergic system and whether there is a possible link to alcohol consumption. We found that lack of FGF-2 reduces the alcohol intake of mice. Transcriptome analysis of DAergic neurons revealed that FGF-2 knockout (FGF-2 KO) shifts the molecular fingerprint of midbrain dopaminergic (mDA) neurons to DA subtypes of the ventral tegmental area (VTA). In line with this, proteomic changes predominantly appear also in the VTA. Interestingly, these changes led to an altered regulation of the FGF-2 signalling cascades and DAergic pathways in a region-specific manner, which was only marginally affected by voluntary alcohol consumption. Thus, lack of FGF-2 not only affects the gene expression but also the proteome of specific brain regions of mDA neurons. Our study provides new insights into the neuroadaptations of the DAergic system during alcohol abuse and, therefore, comprises novel targets for future pharmacological interventions.

Chronic Voluntary Alcohol Consumption Alters Promoter Methylation and Expression of Fgf-2 and Fgfr1

Alcohol abuse accounts for 3.3 million deaths annually, rendering it a global health issue. Recently, fibroblast growth factor 2 (FGF-2) and its target, fibroblast growth factor receptor 1 (FGFR1), were discovered to positively regulate alcohol-drinking behaviors in mice. We tested whether alcohol intake and withdrawal alter DNA methylation of Fgf-2 and Fgfr1 and if there is a correlation regarding mRNA expression of these genes. Blood and brain tissues of mice receiving alcohol intermittently over a six-week period were analyzed using direct bisulfite sequencing and qRT-PCR analysis. Assessment of Fgf-2 and Fgfr1 promoter methylation revealed changes in the methylation of cytosines in the alcohol group compared with the control group. Moreover, we showed that the altered cytosines coincided with binding motives of several transcription factors. We also found that Fgf-2 and Fgfr1 gene expression was significantly decreased in alcohol-receiving mice compared with control littermates, and that this effect was specifically detected in the dorsomedial striatum, a brain region involved in the circuitry of the reward system. Overall, our data showed alcohol-induced alterations in both mRNA expression and methylation pattern of Fgf-2 and Fgfr1. Furthermore, these alterations showed a reward system regional specificity, therefore, resembling potential targets for future pharmacological interventions.

FGF2 is an endogenous regulator of alcohol reward and consumption

Alcohol use disorder (AUD) is a chronic, relapsing disorder, characterized by escalating alcohol drinking and loss of control, with very limited available treatments. We recently reported that the expression of fibroblast growth factor 2 (Fgf2) is increased in the striatum of rodents following long-term excessive alcohol drinking and that the systemic or intra-striatal administration of recombinant FGF2 increases alcohol consumption. Here, we set out to determine whether the endogenous FGF2 plays a role in alcohol drinking and reward, by testing the behavioural phenotype of Fgf2 knockout mice. We found that Fgf2 deficiency resulted in decreased alcohol consumption when tested in two-bottle choice procedures with various alcohol concentrations. Importantly, these effects were specific for alcohol, as a natural reward (sucrose) or water consumption was not affected by Fgf2 deficiency. In addition, Fgf2 knockout mice failed to show alcohol-conditioned place preference (CPP) but showed normal fear conditioning, suggesting that deletion of the growth factor reduces alcohol's rewarding properties. Finally, Fgf2 knockout mice took longer to recover from the loss of righting reflex and showed higher blood alcohol concentrations when challenged with an intoxicating alcohol dose, suggesting that their ethanol metabolism might be affected. Together, our results show that the endogenous FGF2 plays a critical role in alcohol drinking and reward and indicate that FGF2 is a positive regulator of alcohol-drinking behaviours. Our findings suggest that FGF2 is a potential biomarker for problem alcohol drinking and is a potential target for pharmacotherapy development for AUD.

What Can We Learn from FGF-2 Isoform-Specific Mouse Mutants? Differential Insights into FGF-2 Physiology In Vivo

Fibroblast growth factor 2 (FGF-2), ubiquitously expressed in humans and mice, is functionally involved in cell growth, migration and maturation in vitro and in vivo. Based on the same mRNA, an 18-kilo Dalton (kDa) FGF-2 isoform named FGF-2 low molecular weight (FGF-2LMW) isoform is translated in humans and rodents. Additionally, two larger isoforms weighing 21 and 22 kDa also exist, summarized as the FGF-2 high molecular weight (FGF-2HMW) isoform. Meanwhile, the human FGF-2HMW comprises a 22, 23, 24 and 34 kDa protein. Independent studies verified a specific intracellular localization, mode of action and tissue-specific spatiotemporal expression of the FGF-2 isoforms, increasing the complexity of their physiological and pathophysiological roles. In order to analyze their spectrum of effects, FGF-2LMW knock out (ko) and FGF-2HMWko mice have been generated, as well as mice specifically overexpressing either FGF-2LMW or FGF-2HMW. So far, the development and functionality of the cardiovascular system, bone formation and regeneration as well as their impact on the central nervous system including disease models of neurodegeneration, have been examined. This review provides a summary of the studies characterizing the in vivo effects modulated by the FGF-2 isoforms and, thus, offers a comprehensive overview of its actions in the aforementioned organ systems.

Fibroblast Growth Factor: Promising Target for Schizophrenia

Schizophrenia is one of the most debilitating mental disorders around the world. It is characterized by neuroanatomical or biochemical changes. The role of the fibroblast growth factors (FGFs) system in schizophrenia has received considerable attention in recent years. Various changes in the gene expression and/or level of FGFs have been implicated in the etiology, symptoms and progression of schizophrenia. For example, studies have substantiated an interaction between FGFs and the signaling pathway of dopamine receptors. To understand the role of this system in schizophrenia, the databases of Open Access Journals, Web of Science, PubMed (NLM), LISTA (EBSCO), and Google Scholar with keywords including fibroblast growth factors, dopamine, schizophrenia, psychosis, along with neurotrophic were searched. In conclusion, the FGF family represent molecular candidates as new drug targets and treatment targets for schizophrenia.

FGF-2 isoforms influence the development of dopaminergic neurons in the murine substantia nigra, but not anxiety-like behavior, stress susceptibility, or locomotor behavior

BACKGROUND

Loss of fibroblast growth factor 2 (FGF-2) is responsible for the development of an increased number of dopaminergic (DA) neurons in the murine substantia nigra pars compacta (SNpc). Furthermore, dysregulation of its expression patterns within the central nervous system (CNS) is associated with behavioral abnormalities in mice. Until now, the contributions of the individual FGF-2 isoforms (one low (LMW) and two high molecular weight (HMW) isoforms) in the CNS are elusive.

METHODS

To unravel the specific effects of FGF-2 isoforms, we compared three knockout mouse lines, one only deficient for LMW, one deficient for HMW and another lacking both isoforms, regarding DA neuronal development. With this regard, three time points of ontogenic development of the SNpc were stereologically investigated. Furthermore, behavioral aspects were analyzed in young adult mice, supplemented by corticosterone measurements.

RESULTS

Juvenile mice lacking either LMW or HMW develop equal supernumerary DA neuron numbers in the SNpc. Compensatory increased LMW expression is observed in animals lacking HMW. Meanwhile, no knockout mouse line demonstrated changes in anxiety-like behavior, stress susceptibility, or locomotor behavior.

CONCLUSIONS

Both FGF-2 isoforms crucially influence DA neuronal development in the murine SNpc. However, absence of LMW or HMW alone alters neither anxiety-like nor locomotor behavior, or stress susceptibility. Therefore, FGF-2 is not a determinant and causative factor for behavioral alterations alone, but probably in combination with appropriate conditions, like environmental or genetic factors.

Polarized microglia do not influence oligodendrocyte lineage cells via astrocytes

Microglia can adopt different activation patterns, ranging from a pro-inflammatory M1- to an anti-inflammatory M2-like phenotype in which they play crucial roles in various neuroinflammatory diseases. M2-like microglia are described to drive remyelination, whereas detrimental effects have been attributed to M1-like microglia. How polarized microglia might act on oligodendrocyte lineage cells indirectly by influencing astrocytes has not been studied in detail. In this study, conditioned media from polarized murine microglia were used to treat astrocytes and astrocytic gene expression was analyzed by microarray for genes known to influence oligodendrocyte lineage cells. Supernatants of astrocytes previously stimulated with soluble effectors from polarized microglia were used to investigate effects on oligodendrocyte precursor cells (OPC). Growth factors known to induce OPC proliferation, differentiation, and survival were upregulated in astrocytes treated with supernatants from M1-like microglia while M0- and M2-like microglia only had negligible effects on the expression of these factors in astrocytes. Despite the upregulation of these factors in M1 stimulated astrocytes there were no significant effects on OPC in vitro. All astrocyte supernatants induced proliferation of A2B5⁺ OPC and inhibited differentiation of OPC into mature oligodendrocytes. A trend toward enhanced migration of OPC was induced by M1 stimulated astrocytes. Our data suggest that M1-like microglia may potentially influence OPC and remyelination indirectly via astrocytes by inducing the expression of respective growth factors, however, this has no significant effect in addition to the already strong effects of unstimulated astrocytes on OPC. Nevertheless, the observed effect may be of relevance in other pathophysiological scenarios.

The role of fibroblast growth factor 2 in drug addiction

Fibroblast growth factor 2 (FGF2) is a member of the FGF-family, which consists of 22 members, with four known FGF receptors (five in humans). Over the last 30 years, FGF2 has been extensively studied for its role in cell proliferation, differentiation, growth, survival and angiogenesis during development, as well as for its role in adult neurogenesis and regenerative plasticity. Over the past decade, FGF2 has been implicated in learning and memory, as well as in several neuropsychiatric disorders, including anxiety, stress, depression and drug addiction. In this review, we present accumulating evidence indicating the involvement of FGF2 in neuroadaptations caused by drugs of abuse, namely, amphetamine, cocaine, nicotine and alcohol. Moreover, evidence suggests that FGF2 is a positive regulator of alcohol and drug-related behaviors. Thus, although additional studies are yet required, we suggest that reducing FGF2 activity may provide a novel therapeutic approach for substance use disorders.

Deficiency of fibroblast growth factor 2 (FGF-2) leads to abnormal spermatogenesis and altered sperm physiology

In previous studies, we described the presence of fibroblast growth factor 2 (FGF-2) and its receptors (FGFRs) in human testis and sperm, which are involved in spermatogenesis and in motility regulation. The aim of the present study was to analyze the role of FGF-2 in the maintenance of sperm physiology using FGF-2 knockout (KO) mice. Our results showed that in wild-type (WT) animals, FGF-2 is expressed in germ cells of the seminiferous epithelium, in epithelial cells of the epididymis, and in the flagellum and acrosomal region of epididymal sperm. In the FGF-2 KO mice, we found alterations in spermatogenesis kinetics, higher numbers of spermatids per testis, and enhanced daily sperm production compared with the WT males. No difference in the percentage of sperm motility was detected, but a significant increase in sperm concentration and in sperm head abnormalities was observed in FGF-2 KO animals. Sperm from KO mice depicted reduced phosphorylation on tyrosine residues (a phenomenon that was associated with sperm capacitation) and increased acrosomal loss after incubation under capacitating conditions. However, the FGF-2 KO males displayed no apparent fertility defects, since their mating with WT females showed no differences in the time to delivery, litter size, and pup weight in comparison with WT males. Overall, our findings suggest that FGF-2 exerts a role in mammalian spermatogenesis and that the lack of FGF-2 leads to dysregulated sperm production and altered sperm morphology and function. FGF-2-deficient mice constitute a model for the study of the complex mechanisms underlying mammalian spermatogenesis.