Simonetta Camandola

NF-κB in neuronal plasticity and neurodegenerative disorders

NF-κB is widely known for its ubiquitous roles in inflammation and immune responses, as well as in control of cell division and apoptosis. These roles are apparent in the nervous system, but neurons and their neighboring cells employ the NF-κB pathway for distinctive functions as well, ranging from development to the coordination of cellular responses to injury of the nervous system and to brain-specific processes such as the synaptic signaling that underlies learning and memory. Here we discuss the regulation of NF-κB activity by neurotransmitters and neurotrophic factors and the physiological and pathological effects of NF-κB activation in neurons and glial cells. Based on work in animal models, it appears that manipulation of NF-κB signaling may prove valuable in treating such conditions as ischemic stroke, physical trauma to the brain or spinal cord, and neurodegenerative disorders, including Alzheimer’s disease and Parkinson’s disease.

Pivotal role for neuronal Toll-like receptors in ischemic brain injury and functional deficits.

The innate immune system senses the invasion of pathogenic microorganisms and tissue injury through Toll-like receptors (TLR), a mechanism thought to be limited to immune cells. We now report that neurons express several TLRs, and that the levels of TLR2 and -4 are increased in neurons in response to IFN-γ stimulation and energy deprivation. Neurons from both TLR2 knockout and -4 mutant mice were protected against energy deprivation-induced cell death, which was associated with decreased activation of a proapoptotic signaling cascade involving jun N-terminal kinase and the transcription factor AP-1. TLR2 and -4 expression was increased in cerebral cortical neurons in response to ischemia/reperfusion injury, and the amount of brain damage and neurological deficits caused by a stroke were significantly less in mice deficient in TLR2 or -4 compared with WT control mice. Our findings establish a proapoptotic signaling pathway for TLR2 and -4 in neurons that may render them vulnerable to ischemic death.

HNE interacts directly with JNK isoforms in human hepatic stellate cells.

4-Hydroxy-2,3-nonenal (HNE) is an aldehydic end product of lipid peroxidation which has been detected in vivo in clinical and experimental conditions of chronic liver damage. HNE has been shown to stimulate procollagen type I gene expression and synthesis in human hepatic stellate cells (hHSC) which are known to play a key role in liver fibrosis. In this study we investigated the molecular mechanisms underlying HNE actions in cultured hHSC. HNE, at doses compatible with those detected in vivo, lead to an early generation of nuclear HNE-protein adducts of 46, 54, and 66 kD, respectively, as revealed by using a monoclonal antibody specific for HNE-histidine adducts. This observation is related to the lack of crucial HNE-metabolizing enzymatic activities in hHSC. Kinetics of appearance of these nuclear adducts suggested translocation of cytosolic proteins. The p46 and p54 isoforms of c-Jun amino-terminal kinase (JNKs) were identified as HNE targets and were activated by this aldehyde. A biphasic increase in AP-1 DNA binding activity, associated with increased mRNA levels of c-jun, was also observed in response to HNE. HNE did not affect the Ras/ERK pathway, c-fos expression, DNA synthesis, or NF-kappaB binding. This study identifies a novel mechanism linking oxidative stress to nuclear signaling in hHSC. This mechanism is not based on redox sensors and is stimulated by concentrations of HNE compatible with those detected in vivo, and thus may be relevant during chronic liver diseases.

Cellular and Molecular Mechanisms Underlying Perturbed Energy Metabolism and Neuronal Degeneration in Alzheimer's and Parkinson's Diseases

ABSTRACT: Synaptic degeneration and death of nerve cells are defining features of Alzheimers disease (AD) and Parkinsons disease (PD), the two most prevalent age‐related neurodegenerative disorders. In AD, neurons in the hippocampus and basal forebrain (brain regions that subserve learning and memory functions) are selectively vulnerable. In PD dopamine‐producing neurons in the substantia nigra‐striatum (brain regions that control body movements) selectively degenerate. Studies of postmortem brain tissue from AD and PD patients have provided evidence for increased levels of oxidative stress, mitochondrial dysfunction and impaired glucose uptake in vulnerable neuronal populations. Studies of animal and cell culture models of AD and PD suggest that increased levels of oxidative stress (membrane lipid peroxidation, in particular) may disrupt neuronal energy metabolism and ion homeostasis, by impairing the function of membrane ion‐motive ATPases and glucose and glutamate transporters. Such oxidative and metabolic compromise may thereby render neurons vulnerable to excitotoxicity and apoptosis. Studies of the pathogenic mechanisms of AD‐linked mutations in amyloid precursor protein (APP) and presenilins strongly support central roles for perturbed cellular calcium homeostasis and aberrant proteolytic processing of APP as pivotal events that lead to metabolic compromise in neurons. Specific molecular “players” in the neurodegenerative processes in AD and PD are being identified and include Par‐4 and caspases (bad guys) and neurotrophic factors and stress proteins (good guys). Interestingly, while studies continue to elucidate cellular and molecular events occurring in the brain in AD and PD, recent data suggest that both AD and PD can manifest systemic alterations in energy metabolism (e.g., increased insulin resistance and dysregulation of glucose metabolism). Emerging evidence that dietary restriction can forestall the development of AD and PD is consistent with a major “metabolic” component to these disorders, and provides optimism that these devastating brain disorders of aging may be largely preventable.

A synthetic inhibitor of p53 protects neurons against death induced by ischemic and excitotoxic insults, and amyloid β‐peptide

The tumor suppressor protein p53 is essential for neuronal death in several experimental settings and may participate in human neurodegenerative disorders. Based upon recent studies characterizing chemical inhibitors of p53 in preclinical studies in the cancer therapy field, we synthesized the compound pifithrin‐α and evaluated its potential neuroprotective properties in experimental models relevant to the pathogenesis of stroke and neurodegenerative disorders. Pifithrin‐α protected neurons against apoptosis induced by DNA‐damaging agents, amyloid β‐peptide and glutamate. Protection by pifithrin‐α was correlated with decreased p53 DNA‐binding activity, decreased expression of the p53 target gene Bax and suppression of mitochondrial dysfunction and caspase activation. Mice given pifithrin‐α exhibited increased resistance of cortical and striatal neurons to focal ischemic injury and of hippocampal neurons to excitotoxic damage. These preclinical studies demonstrate the efficacy of a p53 inhibitor in models of stroke and neurodegenerative disorders, and suggest that drugs that inhibit p53 may reduce the extent of brain damage in related human neurodegenerative conditions.

Hormetic dietary phytochemicals

Compelling evidence from epidemiological studies suggests beneficial roles of dietary phytochemicals in protecting against chronic disorders such as cancer, and inflammatory and cardiovascular diseases. Emerging findings suggest that several dietary phytochemicals also benefit the nervous system and, when consumed regularly, may reduce the risk of disorders such as Alzheimer’s and Parkinson’s diseases. The evidence supporting health benefits of vegetables and fruits provide a rationale for identification of the specific phytochemicals responsible, and for investigation of their molecular and cellular mechanisms of action. One general mechanism of action of phytochemicals that is emerging from recent studies is that they activate adaptive cellular stress response pathways. From an evolutionary perspective, the noxious properties of such phytochemicals play an important role in dissuading insects and other pests from eating the plants. However at the subtoxic doses ingested by humans that consume the plants, the phytochemicals induce mild cellular stress responses. This phenomenon has been widely observed in biology and medicine, and has been described as ‘preconditioning’ or ‘hormesis.’ Hormetic pathways activated by phytochemicals may involve kinases and transcription factors that induce the expression of genes that encode antioxidant enzymes, protein chaperones, phase-2 enzymes, neurotrophic factors, and other cytoprotective proteins. Specific examples of such pathways include the sirtuin–FOXO pathway, the NF-κB pathway, and the Nrf-2/ARE pathway. In this article, we describe the hormesis hypothesis of phytochemical actions with a focus on the Nrf2/ARE signaling pathway as a prototypical example of a neuroprotective mechanism of action of specific dietary phytochemicals.

Evidence that accumulation of ceramides and cholesterol esters mediates oxidative stress-induced death of motor neurons in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motor neurons in the spinal cord resulting in progressive paralysis and death. The pathogenic mechanism of ALS is unknown but may involve increased oxidative stress, overactivation of glutamate receptors, and apoptosis. We report abnormalities in sphingolipid and cholesterol metabolism in the spinal cords of ALS patients and in a transgenic mouse model (Cu/ZnSOD mutant mice), which manifest increased levels of sphingomyelin, ceramides, and cholesterol esters; in the Cu/ZnSOD mutant mice, these abnormalities precede the clinical phenotype. In ALS patients and Cu/Zn‐SOD mutant mice, increased oxidative stress occurs in association with the lipid alterations, and exposure of cultured motor neurons to oxidative stress increases the accumulation of sphingomyelin, ceramides, and cholesterol esters. Pharmacological inhibition of sphingolipid synthesis prevents accumulation of ceramides, sphingomyelin, and cholesterol esters and protects motor neurons against death induced by oxidative and excitotoxic insults. These findings suggest a pivotal role for altered sphingolipid metabolism in the pathogenesis of ALS.

NF-κB as a therapeutic target in neurodegenerative diseases

NF-κB is a transcription factor that regulates numerous physiological functions, and that is involved in the pathogenesis of various diseases. In the nervous system there is evidence supporting a dual role of NF-κB in neurodegenerative diseases; activation of NF-κB in neurons promotes their survival, whereas activation in glial and immune cells mediates pathological inflammatory processes. The reason for such a dichotomy lies in the complexity of the NF-κB system. Emerging research has begun to dissect the pathways leading to the activation of the different NF-κB proteins, and the gene targets of NF-κB, in cells of the nervous system. In this article the authors discuss recent findings concerning the roles of NF-κB in the pathogenesis of several neurodegenerative disorders, and its potential as a pharmaceutical target for these disorders.

Plumbagin, a novel Nrf2/ARE activator, protects against cerebral ischemia

J. Neurochem. (2010) 112, 1316–1326.

Evidence for miR-181 involvement in neuroinflammatory responses of astrocytes.

Inflammation is a common component of acute injuries of the central nervous system (CNS) such as ischemia, and degenerative disorders such as Alzheimers disease. Glial cells play important roles in local CNS inflammation, and an understanding of the roles for microRNAs in glial reactivity in injury and disease settings may therefore lead to the development of novel therapeutic interventions. Here, we show that the miR‐181 family is developmentally regulated and present in high amounts in astrocytes compared to neurons. Overexpression of miR‐181c in cultured astrocytes results in increased cell death when exposed to lipopolysaccharide (LPS). We show that miR‐181 expression is altered by exposure to LPS, a model of inflammation, in both wild‐type and transgenic mice lacking both receptors for the inflammatory cytokine TNF‐α. Knockdown of miR‐181 enhanced LPS‐induced production of pro‐inflammatory cytokines (TNF‐α, IL‐6, IL‐1β, IL‐8) and HMGB1, while overexpression of miR‐181 resulted in a significant increase in the expression of the anti‐inflammatory cytokine IL‐10. To assess the effects of miR‐181 on the astrocyte transcriptome, we performed gene array and pathway analysis on astrocytes with reduced levels of miR‐181b/c. To examine the pool of potential miR‐181 targets, we employed a biotin pull‐down of miR‐181c and gene array analysis. We validated the mRNAs encoding MeCP2 and X‐linked inhibitor of apoptosis as targets of miR‐181. These findings suggest that miR‐181 plays important roles in the molecular responses of astrocytes in inflammatory settings. Further understanding of the role of miR‐181 in inflammatory events and CNS injury could lead to novel approaches for the treatment of CNS disorders with an inflammatory component.