Plasma membrane calcium ATPase downregulation in dopaminergic neurons alters cellular physiology and motor behaviour in Drosophila melanogaster.

The accumulation of Ca2+ and its subsequent increase in oxidative stress is proposed to be involved in selective dysfunctionality of dopaminergic neurons, the main cell type affected in Parkinson's disease. To test the in vivo impact of Ca2+ increment in dopaminergic neurons physiology, we downregulated the plasma membrane Ca2+ ATPase (PMCA), a pump that extrudes cytosolic Ca2+ , by expressing PMCARNAi in Drosophila melanogaster dopaminergic neurons. In these animals, we observed major locomotor alterations paralleled to higher cytosolic Ca2+ and increased levels of oxidative stress in mitochondria. Interestingly, although no overt degeneration of dopaminergic neurons was observed, evidences of neuronal dysfunctionality were detected such as increases in presynaptic vesicles in dopaminergic neurons and in the levels of dopamine in the brain, as well as presence of toxic effects when PMCA was downregulated in the eye. Moreover, reduced PMCA levels were found in a Drosophila model of Parkinson's disease, Parkin knock-out, expanding the functional relevance of PMCA reduction to other Parkinson's disease-related models. In all, we have generated a new model to study motor abnormalities caused by increments in Ca2+ that lead to augmented oxidative stress in a dopaminergic environment, added to a rise in synaptic vesicles and dopamine levels.

Cell therapy for Parkinson's disease is coming of age: current challenges and future prospects with a focus on immunomodulation.

Parkinson's disease (PD) is a neurodegenerative disease that affects more than 1% of people over the age of 60. The principal feature of this disease is the progressive loss of dopaminergic neurons (DAn) within the nigrostriatal system, causing the motor symptoms observed in these patients. At present, there is no therapeutic approach with a cytoprotective effect that can prevent DAn cell death or disease progression. Cell replacement therapy began 30 years ago with the objective to compensate for the loss of DAn by transplantation of dopamine-producing cells. The results from these trials have provided proof of concept of safety and efficacy of cell replacement. However, a major limiting factor of this strategy has been the poor survival rate of grafted DAn. An important factor that could cause cell death of DA precursors is the host response to the graft. In this review, we discuss the factors that affect the outcome of cell therapy in PD, with focus on the cell types used and the functional effects of the host immune response on graft survival and differentiation. We also discuss the strategies that may increase the efficacy of cell replacement therapy which target the host immune response.

A new focal model resembling features of cortical pathology of the progressive forms of multiple sclerosis: Influence of innate immunity.

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of unknown aetiology that causes neurological disabilities in young adults. MS displays different clinical patterns, including recurrent episodes with remission periods ("relapsing-remitting MS" (RRMS)), which can progress over several years to a secondary progressive form (SPMS). However, 10% of patients display persistent progression at the onset of disease ("primary progressive MS" (PPMS)). Currently, no specific therapeutic agents are available for the progressive forms, mainly because the underlying pathogenic mechanisms are not clear and because no animal models have been specifically developed for these forms. The development of MS animal models is required to clarify the pathological mechanisms and to test novel therapeutic agents. In the present work, we overexpressed interleukin 1 beta (IL-1ß) in the cortex to develop an animal model reflecting the main pathological hallmarks of MS. The treated animals presented with neuroinflammation, demyelination, glial activation, and neurodegeneration along with cognitive symptoms and MRI images consistent with MS pathology. We also demonstrated the presence of meningeal inflammation close to cortical lesions, with characteristics similar to those described in MS patients. Systemic pro-inflammatory stimulation caused a flare-up of the cortical lesions and behavioural symptoms, including impairment of working memory and the appearance of anxiety-like symptoms. Our work demonstrated induced cortical lesions, reflecting the main histopathological hallmarks and cognitive impairments characterizing the cortical pathology described in MS patients with progressive forms of the disease.

Glial Cell-Elicited Activation of Brain Microvasculature in Response to Brucella abortus Infection Requires ASC Inflammasome-Dependent IL-1ß Production.

Blood-brain barrier activation and/or dysfunction are a common feature of human neurobrucellosis, but the underlying pathogenic mechanisms are largely unknown. In this article, we describe an immune mechanism for inflammatory activation of human brain microvascular endothelial cells (HBMEC) in response to infection with Brucella abortus Infection of HBMEC with B. abortus induced the secretion of IL-6, IL-8, and MCP-1, and the upregulation of CD54 (ICAM-1), consistent with a state of activation. Culture supernatants (CS) from glial cells (astrocytes and microglia) infected with B. abortus also induced activation of HBMEC, but to a greater extent. Although B. abortus-infected glial cells secreted IL-1ß and TNF-α, activation of HBMEC was dependent on IL-1ß because CS from B. abortus-infected astrocytes and microglia deficient in caspase-1 and apoptosis-associated speck-like protein containing a CARD failed to induce HBMEC activation. Consistently, treatment of CS with neutralizing anti-IL-1ß inhibited HBMEC activation. Both absent in melanoma 2 and Nod-like receptor containing a pyrin domain 3 are partially required for caspase-1 activation and IL-1ß secretion, suggesting that multiple apoptosis-associated speck-like protein containing CARD-dependent inflammasomes contribute to IL-1ß-induced activation of the brain microvasculature. Inflammasome-mediated IL-1ß secretion in glial cells depends on TLR2 and MyD88 adapter-like/TIRAP. Finally, neutrophil and monocyte migration across HBMEC monolayers was increased by CS from Brucella-infected glial cells in an IL-1ß-dependent fashion, and the infiltration of neutrophils into the brain parenchyma upon intracranial injection of B. abortus was diminished in the absence of Nod-like receptor containing a pyrin domain 3 and absent in melanoma 2. Our results indicate that innate immunity of the CNS set in motion by B. abortus contributes to the activation of the blood-brain barrier in neurobrucellosis and IL-1ß mediates this phenomenon.

Fibulin-2 is a key mediator of the pro-neurogenic effect of TGF-beta1 on adult neural stem cells.

Transforming growth factor beta 1 (TGF-beta1), an anti-inflammatory cytokine, has been shown to have pro-neurogenic effects on adult Neural Stem Cells (aNSC) from the dentate gyrus and in vivo models. Here, we expanded the observation of the pro-neurogenic effect of TGF-beta1 on aNSC from the subventricular zone (SVZ) of adult rats and performed a functional genomic analysis to identify candidate genes to mediate its effect. 10 candidate genes were identified by microarray analysis and further validated by qRT-PCR. Of these, Fibulin-2 was increased 477-fold and its inhibition by siRNA blocks TGF-beta1 pro-neurogenic effect. Curiously, Fibulin-2 was not expressed by aNSC but by a GFAP-positive population in the culture, suggesting an indirect mechanism of action. TGF-beta1 also induced Fibulin-2 in the SVZ in vivo. Interestingly, 5 out of the 10 candidate genes identified are known to interact with integrins, paving the way for exploring their functional role in adult neurogenesis. In conclusion, we have identified 10 genes with putative pro-neurogenic effects, 5 of them related to integrins and provided proof that Fibulin-2 is a major mediator of the pro-neurogenic effects of TGF-beta1. These data should contribute to further exploring the molecular mechanism of adult neurogenesis of the genes identified and the involvement of the integrin pathway on adult neurogenesis.

Special issue commentary: the changing face of inflammation in the brain.

The study of inflammation in the brain has been extended to include a wide range of conditions, but there remains plenty of argument over semantics and the precise definition of what constitutes inflammation in these pathologies. In this special issue, we sought to highlight the diversity of what is considered to be inflammation in the brain, and we have accepted that the presence of microglia cells with altered morphology remains a useful starting point. However, it is clear that whatever is the molecular expression profile that accompanies an activated microglial cell, it is not static and it is influenced by factors both intrinsic and extrinsic to the brain. This article is part of a Special Issue entitled 'Neuroinflammation in neurodegeneration and neurodysfunction'.

Do immunosuppressive treatments influence immune responses against adenovirus-based COVID-19 vaccines in patients with multiple sclerosis? An Argentine multicenter study.

Introduction: There are no reports in LATAM related to longitudinal humoral and cellular response to adenovirus based COVID-19 vaccines in people with Multiple Sclerosis (pwMS) under different disease modifying therapies (DMTs) and neutralization of the Omicron and Wuhan variants of SARS-COV-2. Methods: IgG anti- SARS-COV-2 spike titer were measured in a cohort of 101 pwMS under fingolimod, dimethyl fumarate, cladribine and antiCD20, as well as 28 healthy controls (HC) were measured 6 weeks after vaccination with 2nd dose (Sputnik V or AZD1222) and 3nd dose (homologous or heterologous schedule). Neutralizing capacity was against Omicron (BA.1) and Wuhan (D614G) variants and pseudotyped particles and Cellular response were analyzed. Results: Multivariate regression analysis showed anti-cd20 (ß= -,349, 95% CI: -3655.6 - -369.01, p=0.017) and fingolimod (ß=-,399, 95% CI: -3363.8 - -250.9, p=0.023) treatments as an independent factor associated with low antibody response (r2 adjusted=0.157). After the 2nd dose we found a correlation between total and neutralizing titers against D614G (rho=0.6; p<0.001; slope 0.8, 95%CI:0.4-1.3), with no differences between DMTs. Neutralization capacity was lower for BA.1 (slope 0.3, 95%CI:0.1-0.4). After the 3rd dose, neutralization of BA.1 improved (slope: 0.9 95%CI:0.6-1.2), without differences between DMTs. A fraction of pwMS generated anti-Spike CD4+ and CD8+ T cell response. In contrast, pwMS under antiCD20 generated CD8+TNF+IL2+ response without differences with HC, even in the absence of humoral response. The 3rd dose significantly increased the neutralization against the Omicron, as observed in the immunocompetent population. Discussion: Findings regarding humoral and cellular response are consistent with previous reports.

Notch signaling proteins HES-1 and Hey-1 bind to insulin degrading enzyme (IDE) proximal promoter and repress its transcription and activity: implications for cellular Aß metabolism.

Cerebral amyloid ß (Aß) accumulation is pathogenically associated with sporadic Alzheimer's disease (SAD). BACE-1 is involved in Aß generation while insulin-degrading enzyme (IDE) partakes in Aß proteolytic clearance. Vulnerable regions in AD brains show increased BACE-1 protein levels and enzymatic activity while the opposite occurs with IDE. Another common feature in SAD brains is Notch1 overexpression. Here we demonstrate an increase in mRNA levels of Hey-1, a Notch target gene, and a decrease of IDE transcripts in the hippocampus of SAD brains as compared to controls. Transient transfection of Notch intracellular domain (NICD) in N2aSW cells, mouse neuroblastoma cells (N2a) stably expressing human amyloid precursor protein (APP) Swedish mutation, reduce IDE mRNA levels, promoting extracellular Aß accumulation. Also, NICD, HES-1 and Hey-1 overexpression result in decreased IDE proximal promoter activity. This effect was mediated by 2 functional sites located at -379/-372 and -310-303 from the first translation start site in the -575/-19 (556 bp) fragment of IDE proximal promoter. By site-directed mutagenesis of the IDE promoter region we reverted the inhibitory effect mediated by NICD transfection suggesting that these sites are indeed responsible for the Notch-mediated inhibition of the IDE gene expression. Intracranial injection of the Notch ligand JAG-1 in Tg2576 mice, expressing the Swedish mutation in human APP, induced overexpression of HES-1 and Hey-1 and reduction of IDE mRNA levels, respectively. Our results support our theory that a Notch-dependent IDE transcriptional modulation may impact on Aß metabolism providing a functional link between Notch signaling and the amyloidogenic pathway in SAD.

Differential vulnerability of adult neurogenesis by adult and prenatal inflammation: role of TGF-ß1.

Peripheral inflammation, both during the prenatal period and in adulthood, impairs adult neurogenesis. We hypothesized that, similar to other programming effects of prenatal treatments, only prenatal inflammation causes long-term consequences in adult neurogenesis and its neurogenic niche. To test this, pregnant Wistar rats were subcutaneously injected with lipopolysaccharide (LPS; 0.5 mg/kg) or saline solution every other day from gestational/embryonic day (GD) 14-20. In addition adult animals were injected with a single intraperitoneal saline or LPS injection (1 mg/kg) and the effects on neurogenesis were assessed 7 days later. Alternatively, to evaluate long-term consequences of adult LPS injections, LPS (1 mg/kg) was administered peripherally to adult rats four times every other day, and the effects on neurogenesis were assessed 60 days later. Prenatal and adult LPS treatments reduced adult neurogenesis and provoked specific microglial (but not astroglial) activation in the dentate gyrus (DG). However, only prenatal inflammation-mediated effects were long-lasting (at least 60 days). Moreover, these effects were specific to the DG since the Subventricular Zone (SVZ) and the Rostral Migratory Stream (RMS) were not affected. In addition, these stimuli caused differential effects on the molecular components of the neurogenic niche; only prenatal LPS treatment reduced the local levels of TGF-ß1 mRNA in the DG. Finally, TGF-ß1 exerted its pro-neurogenic effects via the Smad 2/3 pathway in a neural stem cell culture. Taken together, these data add evidence to the duration, regional specificity and dramatic consequences of prenatal immune programming on CNS physiology, compared with the limited response observed in the adult brain.

Microglia-secreted TNF-α affects differentiation efficiency and viability of pluripotent stem cell-derived human dopaminergic precursors.

Disease is a neurodegenerative disorder characterised by the progressive loss of dopaminergic cells of the substantia nigra pars compacta. Even though successful transplantation of dopamine-producing cells into the striatum exhibits favourable effects in animal models and clinical trials; transplanted cell survival is low. Since every transplant elicits an inflammatory response which can affect cell survival and differentiation, we aimed to study in vivo and in vitro the impact of the pro-inflammatory environment on human dopaminergic precursors. We first observed that transplanted human dopaminergic precursors into the striatum of immunosuppressed rats elicited an early and sustained activation of astroglial and microglial cells after 15 days' post-transplant. This long-lasting response was associated with Tumour necrosis factor alpha expression in microglial cells. In vitro, conditioned media from activated BV2 microglial cells increased cell death, decreased Tyrosine hydroxylase-positive cells and induced morphological alterations on human neural stem cells-derived dopaminergic precursors at two differentiation stages: 19 days and 28 days. Those effects were ameliorated by inhibition of Tumour necrosis factor alpha, a cytokine which was previously detected in vivo and in conditioned media from activated BV-2 cells. Our results suggest that a pro-inflammatory environment is sustained after transplantation under immunosuppression, providing a window of opportunity to modify this response to increase transplant survival and differentiation. In addition, our data show that the microglia-derived pro-inflammatory microenvironment has a negative impact on survival and differentiation of dopaminergic precursors. Finally, Tumour necrosis factor alpha plays a key role in these effects, suggesting that this cytokine could be an interesting target to increase the efficacy of human dopaminergic precursors transplantation in Parkinson's Disease.

Downregulation of Plasma Membrane Ca2+ ATPase driven by tyrosine hydroxylase-Gal4 reduces Drosophila lifespan independently of effects in neurons.

In Drosophila melanogaster, several Gal4 drivers are used to direct gene/RNAi expression to different dopaminergic neuronal clusters. We previously developed a fly model of Parkinson's disease, in which dopaminergic neurons had elevated cytosolic Ca2+ due to the expression of a Plasma Membrane Ca2+ ATPase (PMCA) RNAi under the thyroxine hydroxylase (TH)-Gal4 driver. Surprisingly, TH-Gal4>PMCARNAi flies died earlier compared to controls and showed swelling in the abdominal area. Flies expressing the PMCARNAi under other TH drivers also showed such swelling and shorter lifespan. Considering that TH-Gal4 is also expressed in the gut, we proposed to suppress the expression specifically in the nervous system, while maintaining the activation in the gut. Therefore, we expressed Gal80 under the direction of the panneuronal synaptobrevin (nSyb) promoter in the context of TH-Gal4. nSyb-Gal80; TH-Gal4>PMCARNAi flies showed the same reduction of survival as TH-Gal4>PMCARNAi flies, meaning that the phenotype of abdomen swelling and reduced survival could be due to the expression of the PMCARNAi in the gut. In perimortem stages TH-Gal4>PMCARNAi guts had alteration in the proventriculi and crops. The proventriculi appeared to lose cells and collapse on itself, and the crop increased its size several times with the appearance of cellular accumulations at its entrance. No altered expression or phenotype was observed in flies expressing PMCARNAi in the dopaminergic PAM cluster (PAM-Gal4>PMCARNAi). In this work we show the importance of checking the global expression of each promoter and the relevance of the inhibition of PMCA expression in the gut.

CNS response to a second pro-inflammatory event depends on whether the primary demyelinating lesion is active or resolved.

Interleukin-1ß (IL-1ß) is considered to be one of the most important mediators in the pathogenesis of inflammatory diseases, particularly in neurodegenerative diseases such as multiple sclerosis (MS). MS is a chronic inflammatory disease characterized by demyelination and remyelination events, with unpredictable relapsing and remitting episodes that seldom worsen MS lesions. We proposed to study the effect of a unique component of the inflammatory process, IL-1ß, and evaluate its effect in repeated episodes, similar to the relapsing-remitting MS pathology. Using adenoviral vectors, we developed a model of focal demyelination/remyelination triggered by the chronic expression of IL-1ß. The long-term expression of IL-1ß in the striatum produced blood-brain barrier (BBB) breakdown, demyelination, microglial/macrophage activation, and neutrophil infiltration but no overt neuronal degeneration. This demyelinating process was followed by complete remyelination of the area. This simple model allows us to study demyelination and remyelination independently of the autoimmune and adaptive immune components. Re-exposure to this cytokine when the first inflammatory response was still unresolved generated a lesion with decreased neuroinflammation, demyelination, axonal injury and glial response. However, a second long-term expression of IL-1ß when the first lesion was resolved could not be differentiated from the first event. In this study, we demonstrated that the response to a second inflammatory stimulus varies depending on whether the initial lesion is still active or has been resolved. Considering that anti-inflammatory treatments have shown little improvement in MS patients, studies about the behavior of specific components of the inflammatory process should be taken into account to develop new therapeutic tools.

Understanding the role of the blood brain barrier and peripheral inflammation on behavior and pathology on ongoing confined cortical lesions.

BACKGROUND: Inflammation in the Central Nervous System (CNS) is associated with blood brain barrier (BBB) breakdown during the early stages of Multiple Sclerosis (MS), indicating a facilitated entry of waves of inflammatory cells from the circulation to the CNS. In the progressive forms of MS, as the lesion becomes chronic, the inflammation remains trapped within the CNS compartment forming the slow evolving lesion, characterized by low inflammation and microglia activation at the lesions edges. The chronic expression of interleukin 1ß (IL-1ß) in the cortex induces BBB breakdown, demyelination, neurodegeneration, microglial/macrophage activation and impaired cognitive performance. The latter can be improved, as long as the BBB recovers and the lesion presents low inflammation. Here, we study the effects of peripheral inflammation on cortical central lesions after the restoration of the BBB, in order to elucidate the role of the peripheral inflammation on these lesions with intact BBB, as it occurs in the progressive forms of MS. MATERIALS AND METHODS: Cortical lesions and peripheral inflammation were induced by the chronic expression of IL-1ß using an adenovector. We performed histological, immunohistochemistry on brain tissue and behavioural analyses. RESULTS: The effects of the chronic expression of IL-1ß in the cortex resolved within 56 days. However, peripheral and sustained inflammation re-opened the BBB, allowing the reappearance of the neuroinflammatory processes within the cortical lesions, increased demyelination and neurodegeneration, and an increase of the behavioral symptoms, such as cognitive impairment and anxiety-like symptoms. CONCLUSIONS: The early treatment of peripheral inflammatory processes should be considered in order to protect the brain from exacerbation of the ongoing neurodegenerative process.

Brucella abortus induces the secretion of proinflammatory mediators from glial cells leading to astrocyte apoptosis.

Central nervous system (CNS) invasion by bacteria of the genus Brucella results in an inflammatory disorder called neurobrucellosis. In this study we present in vivo and in vitro evidence that B. abortus and its lipoproteins activate the innate immunity of the CNS, eliciting an inflammatory response that leads to astrogliosis, a characteristic feature of neurobrucellosis. Intracranial injection of heat-killed B. abortus (HKBA) or outer membrane protein 19 (Omp19), a B. abortus lipoprotein model, induced astrogliosis in mouse striatum. Moreover, infection of astrocytes and microglia with B. abortus induced the secretion of interleukin (IL)-6, IL-1beta, tumor necrosis factor (TNF)-alpha, macrophage chemoattractant protein-1, and KC (CXCL1). HKBA also induced these inflammatory mediators, suggesting the involvement of a structural component of the bacterium. Accordingly, Omp19 induced the same cytokine and chemokine secretion pattern. B. abortus infection induced astrocyte, but not microglia, apoptosis. Indeed, HKBA and Omp19 elicited not only astrocyte apoptosis but also proliferation, two features observed during astrogliosis. Apoptosis induced by HKBA and L-Omp19 was completely suppressed in cells of TNF receptor p55-/- mice or when the general caspase inhibitor Z-VAD-FMK was added to cultures. Hence, TNF-alpha signaling via TNF receptor (TNFR) 1 through the coupling of caspases determines apoptosis. Our results provide proof of the principle that Brucella lipoproteins could be key virulence factors in neurobrucellosis and that astrogliosis might contribute to neurobrucellosis pathogenesis.

Early and adult hippocampal TGF-ß1 overexpression have opposite effects on behavior.

TGF-ß1 is an anti-inflammatory cytokine that is augmented in the brain of autistic patients and that can affect brain development. In this work, we studied the effects of overexpressing TGF-ß1 in the dentate gyrus of adult or young mice on behavior. TGF-ß1 overexpression during postnatal development led to a long-term decrease in social interaction and to long-term increases in self-grooming and depression-related behaviors. Our analysis shows that these behavioral changes correlate with the long-term downregulation of TGF-ß1 and IL-6 expression in the dentate gyrus, as well as to decreases in the mRNA levels of the synaptic protein neuroligin 3 and in the number of Reelin-positive neurons in the dentate gyrus. In contrast, chronic expression of TGF-ß1 during adulthood led to transient opposite effects on these behaviors. These results show a central role of hippocampal TGF-ß1 in the programming and modulation of social interaction, repetitive behavior and depression-related behavior. Finally, our data suggest a role of hippocampal TGF-ß1 and early-life neuroinflammation in the development of the behavioral alterations observed in autism spectrum disorders.

A familiar study on self-limited childhood epilepsy patients using hIPSC-derived neurons shows a bias towards immaturity at the morphological, electrophysiological and gene expression levels.

BACKGROUND: Self-limited Childhood Epilepsies are the most prevalent epileptic syndrome in children. Its pathogenesis is unknown. In this disease, symptoms resolve spontaneously in approximately 50% of patients when maturity is reached, prompting to a maturation problem. The purpose of this study was to understand the molecular bases of this disease by generating and analyzing induced pluripotent stem cell-derived neurons from a family with 7 siblings, among whom 4 suffer from this disease. METHODS: Two affected siblings and, as controls, a healthy sister and the unaffected mother of the family were studied. Using exome sequencing, a homozygous variant in the FYVE, RhoGEF and PH Domain Containing 6 gene was identified in the patients as a putative genetic factor that could contribute to the development of this familial disorder. After informed consent was signed, skin biopsies from the 4 individuals were collected, fibroblasts were derived and reprogrammed and neurons were generated and characterized by markers and electrophysiology. Morphological, electrophysiological and gene expression analyses were performed on these neurons. RESULTS: Bona fide induced pluripotent stem cells and derived neurons could be generated in all cases. Overall, there were no major shifts in neuronal marker expression among patient and control-derived neurons. Compared to two familial controls, neurons from patients showed shorter axonal length, a dramatic reduction in synapsin-1 levels and cytoskeleton disorganization. In addition, neurons from patients developed a lower action potential threshold with time of in vitro differentiation and the amount of current needed to elicit an action potential (rheobase) was smaller in cells recorded from NE derived from patients at 12 weeks of differentiation when compared with shorter times in culture. These results indicate an increased excitability in patient cells that emerges with the time in culture. Finally, functional genomic analysis showed a biased towards immaturity in patient-derived neurons. CONCLUSIONS: We are reporting the first in vitro model of self-limited childhood epilepsy, providing the cellular bases for future in-depth studies to understand its pathogenesis. Our results show patient-specific neuronal features reflecting immaturity, in resonance with the course of the disease and previous imaging studies.

The more you have, the less you get: the functional role of inflammation on neuronal differentiation of endogenous and transplanted neural stem cells in the adult brain.

The differentiation of neural stem cells toward a neuronal phenotype is determined by the extracellular and intracellular factors that form the neurogenic niche. In this review, we discuss the available data on the functional role of inflammation and in particular, pro- and anti-inflammatory cytokines, on neuronal differentiation from endogenous and transplanted neural stem/progenitor cells. In addition, we discuss the role of microglial cell activation on these processes and the fact that microglial cell activation is not univocally associated with a pro-inflammatory milieu. We conclude that brain cytokines could be regarded as part of the endogenous neurogenic niche. In addition, we propose that accumulating evidence suggests that pro-inflammatory cytokines have a negative effect on neuronal differentiation, while anti-inflammatory cytokines exert an opposite effect. The clarification of the functional role of cytokines on neuronal differentiation will be relevant not only to better understand adult neurogenesis, but also to envisage complementary treatments to modulate cytokine action that could increase the therapeutic benefit of future progenitor/stem cell-based therapies.

Chronic expression of low levels of tumor necrosis factor-alpha in the substantia nigra elicits progressive neurodegeneration, delayed motor symptoms and microglia/macrophage activation.

Inflammation, and in particular microglia activation, is regarded as a constant component of brain pathology in Parkinson's disease (PD). Microglial activation has been found in the substantia nigra (SN), one of the main brain regions affected in PD, for many years after the initiation of the disease. Although many studies point towards a deleterious role of inflammation on PD, the functional role of many of its main components has not been clarified yet. For example, tumor necrosis factor-alpha (TNF-alpha), a key pro-inflammatory cytokine, has been shown to exert toxic or no effects on the viability of dopaminergic neurons. No study has evaluated the effects of the long-lasting TNF-alpha expression in the SN, an experimental set-up most probably resembling the clinical situation. The aim of this study was to investigate the effects of the chronic expression of TNF-alpha in the adult SN at different time points. Adenoviral expression of low TNF-alpha levels (17-19 pg/mg) lasted for 14 days in the SN and did not induce interleukin-1beta (IL-1beta) expression. Long-lasting TNF-alpha expression caused dopaminergic cell death from day 14, increasing at 21 and 28 days compared with control animals injected with adenovectors expressing beta-galactosidase. TNF-alpha overexpression elicited irreversible, unilateral akinesia starting at 14 days, but not earlier. These effects were accompanied by microglial activation to stage 4 and/or monocyte/macrophage recruitment from the periphery from day 7 post adenovector inoculations. Thus, we conclude that extended duration of the expression of TNF-alpha is necessary and sufficient for a univocal toxic effect of TNF-alpha on dopaminergic neurons and motor disabilities. This study provides an animal model to study early events that lead to TNF-alpha-mediated neuronal demise in the SN. In addition, the cellular components of the inflammation elicited by TNF-alpha and the lack of IL-1beta expression support the growing idea of a distinct cytokine network in the brain.

Prenatal inflammation impairs adult neurogenesis and memory related behavior through persistent hippocampal TGFß1 downregulation.

Prenatal exposure to inflammatory stimuli is known to influence adult brain function. In addition, adult hippocampal neurogenesis is impaired by a local pro-inflammatory microenvironment. On this basis, we hypothesized that a pro-inflammatory insult during gestation would have negative effects on adult neurogenesis in the offspring. Pregnant Wistar rats received subcutaneous injections of lipopolysaccharide (LPS; 0.5mg/kg) or saline every other day from gestational day 14 to 20. The adult offspring prenatally treated with LPS showed a decrease in the proliferating cells and the newborn neurons of the dentate gyrus. Furthermore, prenatal LPS treatment impaired performance in the neurogenesis-dependent novel object recognition test. Maternal care was impaired by prenatal LPS administration but did not contribute to the effects of prenatal LPS on adult neurogenesis. Persistent microglial activation and downregulated expression of transforming growth factor beta-1 (TGFß(1)) occurred specifically in the adult hippocampus of animals treated prenatally with LPS. Importantly, chronic hippocampal TGFß(1) overexpression restored neurogenesis as well as recognition memory performance to control levels. These findings demonstrate that prenatal inflammation triggered by LPS impairs adult neurogenesis and recognition memory. Furthermore, we provide a model of reduced adult neurogenesis with long-lasting defined alterations in the neurogenic niche. Finally, we show that the expression of a single cytokine (TGFß(1)) in the hippocampus can restore adult neurogenesis and its related behavior, highlighting the role of TGFß(1) in these processes.

Chronic expression of transforming growth factor-beta enhances adult neurogenesis.

Neural stem cells reside in two neurogenic regions of the adult brain: the dentate gyrus of the hippocampus (DG) and the subventricular zone (SVZ). Their proliferation, differentiation, migration and survival are modulated by intrinsic and extrinsic signals, forming a neurogenic niche. Brain cytokines have only been recently regarded as possible components of this neurogenic niche. In particular, we have demonstrated that transforming growth factor-beta (TGF-beta) has a pro-neurogenic effect in the DG in a model of increased neurogenesis by adrenalectomy. We wanted to test whether TGF-beta has a similar effect in another neurogenic region, namely the SVZ. To test this possibility, adult rats were injected with adenoviral vectors expressing TGF-beta (Ad-TGF) or beta-galactosidase (Ad-bgal) in the SVZ and neurogenesis was evaluated 3 weeks later. We have observed that chronic TGF-beta expression increased neurogenesis in the ipsilateral hemisphere of Ad-TGF but not in Ad-bgal-treated rats compared to their contralateral side. In addition, an unspecific effect of the adenoviral vector per se could not be totally discarded. We conclude, under our experimental conditions, that TGF-beta could enhance adult neurogenesis in the SVZ. This data increase the growing evidence supporting a pro-neurogenic role of anti-inflammatory cytokines in the adult brain.