Sustained phosphorylation of mitogen-activated protein kinase is required for basic fibroblast growth factor-mediated axonal branch formation in cultured rat hippocampal neurons

Fibroblast growth factor signaling in axons: from development to disease

The fibroblast growth factor (FGF) family regulates various and important aspects of nervous system development, ranging from the well-established roles in neuronal patterning to more recent and exciting functions in axonal growth and synaptogenesis. In addition, FGFs play a critical role in axonal regeneration, particularly after spinal cord injury, confirming their versatile nature in the nervous system. Due to their widespread involvement in neural development, the FGF system also underlies several human neurological disorders. While particular attention has been given to FGFs in a whole-cell context, their effects at the axonal level are in most cases undervalued. Here we discuss the endeavor of the FGF system in axons, we delve into this neuronal subcompartment to provide an original view of this multipurpose family of growth factors in nervous system (dys)function. Video Abstract.

JNK Signaling Pathway Involvement in Spinal Cord Neuron Development and Death

The c-Jun NH2-terminal protein kinase (JNK) is a Janus-faced kinase, which, in the nervous system, plays important roles in a broad range of physiological and pathological processes. Three genes, encoding for 10 JNK isoforms, have been identified: jnk1, jnk2, and jnk3. In the developing spinal cord, JNK proteins control neuronal polarity, axon growth/pathfinding, and programmed cell death; in adulthood they can drive degeneration and regeneration, after pathological insults. Indeed, recent studies have highlighted a role for JNK in motor neuron (MN) diseases, such as amyotrophic lateral sclerosis and spinal muscular atrophy. In this review we discuss how JNK-dependent signaling regulates apparently contradictory functions in the spinal cord, in both the developmental and adult stages. In addition, we examine the evidence that the specific targeting of JNK signaling pathway may represent a promising therapeutic strategy for the treatment of MN diseases.

Inhibition of FGF Receptor-1 Suppresses Alcohol Consumption: Role of PI3 Kinase Signaling in Dorsomedial Striatum

Excessive alcohol intake leads to mesostriatal neuroadaptations, and to addiction phenotypes. We recently found in rodents that alcohol increases fibroblast growth factor 2 (FGF2) expression in the dorsomedial striatum (DMS), which promotes alcohol consumption. Here, we show that systemic or intra-DMS blockade of the FGF2 receptor, FGF receptor-1 (FGFR1), suppresses alcohol consumption, and that the effects of FGF2-FGFR1 on alcohol drinking are mediated via the phosphoinositide 3 kinase (PI3K) signaling pathway. Specifically, we found that sub-chronic alcohol treatment (7 d × 2.5 g/kg, i.p.) increased Fgfr1 mRNA expression in the dorsal hippocampus and dorsal striatum. However, prolonged and excessive voluntary alcohol consumption in a two-bottle choice procedure increased Fgfr1 expression selectively in DMS. Importantly, systemic administration of the FGFR1 inhibitor PD173074 to mice, as well as its infusion into the DMS of rats, decreased alcohol consumption and preference, with no effects on natural reward consumption. Finally, inhibition of the PI3K, but not of the mitogen-activated protein kinase (MAPK) signaling pathway, blocked the effects of FGF2 on alcohol intake and preference. Our results suggest that activation of FGFR1 by FGF2 in the DMS leads to activation of the PI3K signaling pathway, which promotes excessive alcohol consumption, and that inhibition of FGFR1 may provide a novel therapeutic target for alcohol use disorder.SIGNIFICANCE STATEMENT Long-term alcohol consumption causes neuroadaptations in the mesostriatal reward system, leading to addiction-related behaviors. We recently showed that alcohol upregulates the expression of fibroblast growth factor 2 (FGF2) in dorsomedial striatum (DMS) or rats and mice, and in turn, FGF2 increases alcohol consumption. Here, we show that long-term alcohol intake also increases the expression of the FGF2 receptor, FGFR1 in the DMS. Importantly, inhibition of FGFR1 activity by a selective receptor antagonist reduces alcohol drinking, when given systemically or directly into the DMS. We further show that the effects of FGF2-FGFR1 on alcohol drinking are mediated via activation of the PI3K intracellular signaling pathway, providing an insight on the mechanism for this effect.

EFFECT OF BASIC FIBROBLAST GROWTH FACTOR ON BEHAVIOR ABILITY AND NEURONS OF THE HIPPOCAMPAL CA3 AREA IN ALZHEIMER'S DISEASE MODEL RATS

The study aimed to examine the behavior ability and morphological changes in neuron in the hippocampal CA3 area of Alzheimer's disease (AD) model rats induced by β-amyloid protein (Aβ1–42) and observe the potentiality of the neuroprotective effect of basic fibroblast growth factor (bFGF) on the AD model rats. A total of 70 Wistar rats were randomly divided into the normal control group, the AD model group and the bFGF treatment group. The AD model rats were established by microinjection of Aβ1–42 solution into right hippocampal CA1 area. The bFGF was injected into the abdominal cavity of rats in the bFGF treatment group, and identical volume physiological saline was given for the other two groups. The colorimetric method was used to detect the choline acetyltransferase (ChAT) and acetylcholinesterase (AchE) activity after the behavior capability was determined. Real time-PCR (RT-PCR) was used to evaluate the expression of VEGF mRNA of the rat hippocampal CA3 area. Caspase-3 immunopositive cells in the hippocampal CA3 area were observed under a light microscopy and quantitative analysis were performed by cell morphometric technique. The ultra-microstructure of the neurons was also observed by a transmission electron microscopy (TEM). The results indicated that compared with the AD model group, the learning and memory abilities of the bFGF treatment group were obviously improved and the ChAT activity significantly increased (p < 0.05), whereas the AChE activity, expression of VEGF mRNA and quantity of Caspase-3 immunopositive cells notably decreased (p < 0.05). Under TEM, the neurons in the hippocampal CA3 area of the normal control group had moderate electron density, rule nucleus, integrity perinuclear membrane, evenly distributed chromoplasm and abundant cell organelle, however the neurons of the AD model group showed severely damaged, exhibiting cell body pyknosis, irregular nuclear membranes concentrated, intracytoplasm content concentrated, decreased or unclear organelles. The neuronic pathological lesion of the bFGF treatment group had lessened than that of the AD model group; some of them had distinct neuronal structure and abundant cell organelle. BFGF could efficiently improve the behavior ability and decrease the pathological lesion of hippocampus of the AD model rats, which might promote the neuroprotective effect in the AD.

Implication of fibroblast growth factors in epileptogenesis-associated circuit rearrangements

The transformation of a normal brain in epileptic (epileptogenesis) is associated with extensive morpho-functional alterations, including cell death, axonal and dendritic plasticity, neurogenesis, and others. Neurotrophic factors (NTFs) appear to be very strongly implicated in these phenomena. In this review, we focus on the involvement of fibroblast growth factor (FGF) family members. Available data demonstrate that the FGFs are highly involved in the generation of the morpho-functional alterations in brain circuitries associated with epileptogenesis. For example, data on FGF2, the most studied member, suggest that it may be implicated both in seizure susceptibility and in seizure-induced plasticity, exerting different, and apparently contrasting effects: favoring acute seizures but reducing seizure-induced cell death. Even if many FGF members are still unexplored and very limited information is available on the FGF receptors, a complex and fascinating picture is emerging: multiple FGFs producing synergic or antagonistic effects one with another (and/or with other NTFs) on biological parameters that, in turn, facilitate or oppose transformation of the normal tissue in epileptic. In principle, identifying key elements in these phenomena may lead to effective therapies, but reaching this goal will require confronting a huge complexity. One first step could be to generate a "neurotrophicome" listing the FGFs (and all other NTFs) that are active during epileptogenesis. This should include identification of the extent to which each NTF is active (concentrations at the site of action); how it is active (local representation of receptor subtypes); when in the natural history of disease this occurs; how the NTF at hand will possibly interact with other NTFs. This is extraordinarily challenging, but holds the promise of a better understanding of epileptogenesis and, at large, of brain function.

The phosphoproteomes of Plasmodium falciparum and Toxoplasma gondii reveal unusual adaptations within and beyond the parasites' boundaries

Plasmodium falciparum and Toxoplasma gondii are obligate intracellular apicomplexan parasites that rapidly invade and extensively modify host cells. Protein phosphorylation is one mechanism by which these parasites can control such processes. Here we present a phosphoproteome analysis of peptides enriched from schizont stage P. falciparum and T. gondii tachyzoites that are either "intracellular" or purified away from host material. Using liquid chromatography-tandem mass spectrometry, we identified over 5,000 and 10,000 previously unknown phosphorylation sites in P. falciparum and T. gondii, respectively, revealing that protein phosphorylation is an extensively used regulation mechanism both within and beyond parasite boundaries. Unexpectedly, both parasites have phosphorylated tyrosines, and P. falciparum has unusual phosphorylation motifs that are apparently shaped by its A:T-rich genome. This data set provides important information on the role of phosphorylation in the host-pathogen interaction and clues to the evolutionary forces operating on protein phosphorylation motifs in both parasites.

Signal transduction pathways involved in PPARβ/δ-induced neuronal differentiation

Neuroblastomas are pediatric tumors originating from neuroblasts in the developing peripheral nervous system. The neurotrophin brain-derived neurotrophic factor (BDNF) is a key regulator of survival and differentiation of specific neuronal populations in the central and peripheral nervous system. Patients whose neuroblastoma tumors express high levels of BDNF and TrkB have an unfavorable prognosis. We have previously reported on the neuronal differentiating activity of peroxisome proliferator-activated receptors (PPAR)β/δ natural and synthetic ligands by modulating BDNF/TrkB pathway, suggesting their potential use as new therapeutic strategies for neuroblastoma. The validation of new therapeutic agents implies the understanding of their mechanisms of action. Herein, we report the effects of activated-PPARβ/δ on signal transduction pathways known to be involved in neuronal differentiation, such as ERK1,2 and BDNF pathways. The results obtained, using also PPARβ/δ silencing, indicating a neuronal differentiating effect PPARβ/δ-dependent through BDNF-P75-ERK1,2 pathways, further support a role for PPARβ/δ in neuronal differentiation and pointing towards PPARβ/δ as a modulator of pathways crucial for neuronal differentiation. These findings open new perspectives in the formulation of potential therapeutic approaches to be used as adjuvant treatment with the standard therapies.

The mechanisms underlying fibroblast apoptosis regulated by growth factors during wound healing

While investigating the mechanisms underlying cell death during wound healing processes, we uncovered the pro-apoptotic effects of basic fibroblast growth factor (bFGF) on granulation tissue fibroblasts following pretreatment with transforming growth factor (TGF)-beta1 in vitro. bFGF induced caspase-3 activation and apoptosis in TGF-beta1-pretreated granulation tissue-derived fibroblasts (GF-1) following bFGF treatment for 48 and 96 h. In contrast, fibroblasts that had been treated in the same manner and that originated from the uninjured dermis did not display apoptosis, indicating that the mechanisms underlying apoptosis events in fibroblasts that originate from normal dermal and wound tissues differ. In this process, we also found that bFGF inhibited Akt phosphorylation at serine 473 and induced a rapid loss of phosphorylation of focal adhesion kinase (FAK) at tyrosine 397 in pretreated GF-1 cells, an event that coincided with the dissociation of phosphorylated FAK from the focal adhesions. Therefore, inhibition of survival signals relayed via the disrupted focal adhesion structures and inactivated Akt following bFGF treatment may lead to apoptosis in GF-1 cells pretreated with TGF-beta1. Pretreatment of GF-1 with TGF-beta1 followed by the addition of bFGF resulted in significantly greater inhibition of phosphorylation of Akt and FAK compared to treatment with TGF-beta1 or bFGF alone. The combinatorial treatment also led to proteolysis of FAK and inhibition of FAK and Akt protein expression in GF-1 cells. These findings demonstrated a significant role for the two cytokines in apoptosis of granulation tissue fibroblasts during wound healing. In vivo studies also confirmed a marked decline in phosphorylation and protein expression of Akt and FAK in bFGF-injected skin wounds. These results led to the hypothesis that temporal activation of TGF-beta1 and bFGF at the injury site promotes apoptosis in granulation tissue fibroblasts, an event that is critical for the termination of proliferative granulation tissue formation.

Specificity of the second messenger pathways involved in basic fibroblast growth factor-induced survival and neurite growth in chick ciliary ganglion neurons

Basic fibroblast growth factor (bFGF) exerts multiple neurotrophic actions on cultured neurons from the ciliary ganglion of chick embryo, among them promotion of neuronal survival and of neurite outgrowth. To understand the specificity of the signal transduction cascades involved in the control of these processes, we used pharmacological inhibitors of the three main effectors known to act downstream of the bFGF receptor (FGFR): phospholipase Cgamma (PLCgamma), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase (PI3-K). Neuronal survival was assessed at 24 and 48 hr; neurite growth was analyzed both on dissociated neurons and on explants of whole ganglia. Our data show that only the PI3-K pathway is involved in the survival-promoting effect of bFGF; on the other hand, all three effectors converge on the enhancement of neurite outgrowth, both on isolated neurons and in whole ganglia.

Acute systemic fibroblast growth factor-2 enhances long-term extinction of fear and reduces reinstatement in rats

Despite having made substantial advances in the treatment of anxiety disorders over the past few decades it appears that we have now reached a 'therapeutic impasse'. Further clinical progress requires a greater understanding of the neural mechanisms underlying fear inhibition. In this study, we examined, for the first time, the effects of fibroblast growth factor-2 (FGF2), a mitogen involved in the molecular cascade of memory, on extinction and relapse in rats. In all experiments, rats were first trained to fear a white noise-conditioned stimulus, and then had this learned fear extinguished the following day. Extinction is the process underlying exposure-based therapy in humans. Experiments 1 and 2 demonstrated that FGF2 facilitated the loss of learned fear (ie, extinction) when given either prior to or immediately after extinction but not when given 4 h after extinction. This suggests that FGF2 must be present during the consolidation of the extinction memory to have an effect. Experiment 3 further supported this interpretation by showing that short-term extinction must occur for FGF2 to facilitate long-term extinction, suggesting that FGF2 is facilitating the translation of memory from short-term to long-term storage. In experiment 4 rats given FGF2 immediately after extinction exhibited less shock-induced reinstatement, which is a model preparation of relapse, than did vehicle-treated rats. Together, these experiments demonstrate that FGF2 facilitates extinction and attenuates relapse. Thus, FGF2 may be a novel pharmacological adjunct to exposure therapy.

Divergent effects of the MEKK-1/JNK pathway on NB2a/d1 differentiation: Some activity is required for outgrowth and stabilization of neurites but overactivation inhibits both phenomena

c-Jun N-terminal kinase (JNK), along with its upstream activator MEKK-1, is typically thought of as a stress-activated kinase that mediates apoptosis. However, additional studies indicate that the MEKK-1/JNK pathway mediates critical aspects of neuronal survival and differentiation. Herein, we demonstrate that transfection of differentiated NB2a/d1 cells with a construct expression constitutively activated (ca) MEKK-1 increases levels of phospho-dependent neurofilament (NF) immunoreactivity within perikarya, while expression of a dominant-negative (dn) form of MEKK-1 decreases it. Steady-state levels of perikaryal phospho-NF immunoreactivity are reduced and the increase resulting from expression of caMEKK-1 is prevented, by the JNK inhibitor SP600125, suggesting that JNK is a major downstream effector of MEKK-1 on NF phosphorylation. Unexpectedly, both caMEKK-1 and dnMEKK-1 inhibited neuritogenesis as well as translocation of NFs into newly elaborated neurites. The JNK inhibitor SP600125 also inhibited NF transport in a dose-dependent manner. caMEKK-1 also prevented the increase in NF transport otherwise mediated by MAP kinase. Finally, both caMEKK-1 and dnMEKK-1 prevented initial neuritogenesis. These findings indicate that the MEKK-1/JNK pathway regulates critical aspects of initial outgrowth, and subsequent stabilization of axonal neurites.

Alterations in seizure susceptibility and in seizure-induced plasticity after pharmacologic and genetic manipulation of the fibroblast growth factor-2 system

PURPOSE

The adult brain undergoes activity-dependent plastic modifications during pathologic processes that are reminiscent of those observed during development. For example, seizures induce neuronal loss, neurogenesis, axonal and dendritic sprouting, gliosis, and circuit remodeling. Neurotrophic factors and fibroblast growth factor-2 (FGF-2), in particular, are well-known mediators in each of these cellular events. The aim of this minireview is to summarize and discuss the data supporting the idea that FGF-2 may be involved in seizure generation and in their sequelae.

METHODS

We used epilepsy models of kainate and kindling, with FGF-2 knockout mice and FGF-2 overexpressing mice.

RESULTS

Seizures increase FGF-2 mRNA and protein levels in specific brain areas and upregulate the expression of its receptor FGFR-1. Short-term intrahippocampal injection of FGF-2 cause seizures, whereas long-term i.c.v. infusion of low-dose FGF-2 does not affect kainate seizures but promotes behavioral recovery and reduces hippocampal damage. Kainate seizure severity is not altered in FGF-2 knockout mice, but is increased in FGF-2 overexpressing mice.

CONCLUSIONS

FGF-2 is implicated in seizure susceptibility and in seizure-induced plasticity.

Cdk5 inhibits anterograde axonal transport of neurofilaments but not that of tau by inhibition of mitogen-activated protein kinase activity

Cyclin-dependent kinase 5 (cdk5) inhibits neurofilament (NF) anterograde axonal transport while p42/44 mitogen-activated protein kinase (MAPk) promotes it. Since cdk5 is known to inhibit MAP kinase activity, we examined whether or not cdk5 inhibits anterograde NF transport via inhibition of MAPk activity. To accomplish this, we manipulated the activity of these kinases in differentiated NB2a/d1 cells, and monitored anterograde axonal transport of green fluorescent protein-conjugated-NF-M (GFP-M) and cyan fluorescent protein-conjugated (CFP)-tau. The cdk5 inhibitor roscovitine increased anterograde axonal transport of GFP-M and CFP-tau; transfection with cdk5/p25 inhibited transport of both. Inhibition of MAPk activity by PD98059 or expression of dominant-negative MAPk inhibited anterograde GFP-M transport, while expression of constitutively active MAPk enhanced it; these treatments did not affect CFP-tau transport. PD98059 prevented roscovitine-mediated enhancement of GFP-M transport, but did not prevent enhancement of CFP-tau transport. Co-transfection with constitutively activated MAPk prevented the inhibition of GFP-M transport that normally accompanied transfection with cdk5/p25, but did not prevent inhibition of tau transport by cdk5/p25. Finally, the extent of inhibition of GFP-M axonal transport by PD98059 was not additive to that derived from transfection with cdk5/p35, and the increase in NF transport that accompanies roscovitine treatment was not additive to that derived from transfection with constitutively activated MAPk, suggesting that the influence of these kinases on NF transport was within the same, rather than distinct, pathways. These findings suggest that axonal transport of tau and NFs is under the control of distinct kinase cascades, and that cdk5 inhibits NF transport at least in part by inhibiting MAPk.

Mitogen-activated protein kinase regulates neurofilament axonal transport

Mitogen-activated protein kinase (MAP) kinase plays a pivotal role in the development of the nervous system by mediating both neurogenesis and neuronal differentiation. Here we examined whether p42/44 MAP kinase plays a role in axonal transport and the organization of neurofilaments (NFs) in axonal neurites. Dominant-negative p42/44 MAP kinase, anti-MAP kinase antisense oligonucleotides and the MAP kinase inhibitor PD98059 all reduced NF phospho-epitopes and inhibited anterograde NF axonal transport of GFP-tagged NF subunits in differentiated NB2a/d1 neuroblastoma cells. Expression of constitutively active MAP kinase and intracellular delivery of active enzyme increased NF phospho-epitopes and increased NF axonal transport. Longer treatment with PD98059 shifted NF transport from anterograde to retrograde. PD98059 did not inhibit overall axonal transport nor compromise overall axonal architecture or composition. The p38 MAP kinase inhibitor SB202190 did not inhibit NF transport whereas the kinase inhibitor olomoucine inhibited both NF and mitochondrial transport. Axonal transport of NFs containing NF-H whose C-terminal region was mutated to mimic extensive phosphorylation was substantially less affected by PD98059 compared to a wild-type construct. These data suggest that p42/44 MAP kinase regulates NF anterograde transport by NF C-terminal phosphorylation. MAP kinase may therefore stabilize developing axons by promoting the accumulation of NFs within growing axonal neurites.

Morphological effects of estrogen on cholinergic neurons in vitro involves activation of extracellular signal-regulated kinases

In the present study, we examined the ability of estrogen to enhance cholinergic neurite arborization in vitro and identified the signal transduction cascade associated with this effect. Basal forebrain primordia collected from rat pups on postnatal day 1 were cultured for 2 weeks and then treated with 5 nm 17beta-estradiol for 24 hr. Cholinergic neurons were identified immunocytochemically with an antibody against the vesicular acetylcholine transporter and digitally photographed. Morphological analysis indicated that female cultures respond to estrogen treatment with an increase in total neurite length per neuron (4.5-fold over untreated controls) and in total branch segment number per neuron (2.3-fold over controls). In contrast, there was no change in total neurite length per neuron in male cultures, and we also observed a decrease in total branch segment number per neuron (0.5-fold below controls). Detailed histograms indicated that estrogen increases primary and secondary branch length and number and also increases terminal neuritic branches to the seventh order in female cultures. In a second set of experiments, we investigated the signal transduction cascade involved in this response, and found that an upstream extracellular signal-regulated kinase (ERK) inhibitor blocked the ability of estrogen to enhance outgrowth in female cultures. Our study provides strong evidence in support of the fact that the ERK pathway is required for estrogen-induced structural plasticity in the cholinergic system of female rats. Understanding the intracellular processes that underlie the response of cholinergic neurons to estrogen provides a necessary step in elucidating how cholinergic neurons can be particularly susceptible to degeneration in postmenopausal women.

Transient exposure to FGF2 enhances myelination in embryonic brain cell cocultures

The amount of myelination in vivo and in vitro depends on the number of oligodendrocyte progenitors, their differentiation, and on the neuron function. It has been shown that continuous administration of FGF2, a mitotic and neuroprotective factor, allows oligodendrocyte progenitors to proliferate, but prevents them from differentiating and myelinating. This study was designed to test the effect of transient exposure to FGF2 on myelination in an oligodendrocyte/neuron coculture system. At 2 days in vitro, cultures were treated with a single dose of 20 ng/ml FGF2. Cell proliferation was determined by BrdU uptake. The number of cells of the oligodendrocyte lineage was determined by immunocytology of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase). The maturation of oligodendrocytes and myelination was followed by immunocytological analysis of MBP (myelin basic protein). Electron microscopy was used to study the ultrastructure of myelin. BrdU uptake procedure showed an increase in cell proliferation in FGF2-treated cultures after 48 h of treatment. At 15-18 days in vitro, CNPase(+) and MBP(+) cells were much more abundant in cultures treated with FGF2 than in control cultures. We observed differentiation and maturation of oligodendrocytes and a higher degree of myelination in FGF2-treated cultures compared to controls. Electron microscopy showed the presence of myelin structures in FGF2-treated cultures that did not differ morphologically from those observed in control cultures. Transient exposure of cultured brain cells to FGF2 increased myelination in vitro. Administration of FGF2 over a short period might thus enhance remyelination in demyelinating diseases in vivo.

Fibroblast growth factor-2 increases functional excitatory synapses on hippocampal neurons

The effect of fibroblast growth factor-2 (FGF-2) on synapse formation was investigated using rat cultured hippocampal neurons. Treatment with FGF-2 (0.4-10 ng/mL) for 6 days enhanced synaptogenesis on these neurons by approximately 50%, as determined by counting puncta immunostained for presynaptic- or postsynaptic-specific proteins. This enhancement was statistically significant, and was abolished by a specific inhibitor of mitogen-activated protein kinase (MAPK). The majority of neurons expressed FGF receptors (types 1-3) abundantly on the membrane of somata, dendrites, and growth cones, and in these regions phosphorylation of MAPK was enhanced after FGF-2 application. Furthermore, our experiments showed that the majority of synapses formed in cultures containing FGF-2 were positive both for presynaptic proteins and postsynaptic excitatory synapse-specific proteins, and that these synapses had a similar capacity to recycle the fluorescent styryl dye FM4-64 as those in the control culture. These results indicate that: (i) FGF-2 increases excitatory synapses on hippocampal neurons by activating MAPK activity through FGF receptors; and (ii) synapses formed in FGF-2-treated culture are capable of cycling vesicles.

Transforming growth factor-beta 1 increases bad phosphorylation and protects neurons against damage

Despite the characterization of neuroprotection by transforming growth factor-beta1 (TGF-beta1), the signaling pathway mediating its protective effect is unclear. Bad is a proapoptotic member of the Bcl-2 family and is inactivated on phosphorylation via mitogen-activated protein kinase (MAPK). This study attempted to address whether MAPK signaling and Bad phosphorylation were influenced by TGF-beta1 and, furthermore, whether these two events were involved in the antiapoptotic effect of TGF-beta1. We found a gradual activation of extracellular signal-regulated kinase 1/2 (Erk1/2) and MAPK-activated protein kinase-1 (also called Rsk1) and a concomitant increase in Bad phosphorylation at Ser(112) in mouse brains after adenovirus-mediated TGF-beta1 transduction under nonischemic and ischemic conditions induced by transient middle cerebral artery occlusion. Consistent with these effects, the ischemia-induced increase in Bad protein level and caspase-3 activation were suppressed in TGF-beta1-transduced brain. Consequently, DNA fragmentation, ischemic lesions, and neurological deficiency were significantly reduced. In cultured rat hippocampal cells, TGF-beta1 inhibited the increase in Bad expression caused by staurosporine. TGF-beta1 concentration- and time-dependently activated Erk1/2 and Rsk1 accompanied by an increase in Bad phosphorylation. These effects were blocked by U0126, a mitogen-activated protein kinase/Erk kinase 1/2 inhibitor, suggesting an association between Bad phosphorylation and MAPK activation. Notably, U0126 and a Rsk1 inhibitor (Ro318220) abolished the neuroprotective activity of TGF-beta1 in staurosporine-induced apoptosis, indicating that activation of MAPK is necessary for the antiapoptotic effect of TGF-beta1 in cultured hippocampal cells. Together, we demonstrate that TGF-beta1 suppresses Bad expression under lesion conditions, increases Bad phosphorylation, and activates the MAPK/Erk pathway, which may contribute to its neuroprotective activity.