Hormesis: a promising strategy to sustain endogenous neuronal survival pathways against neurodegenerative disorders

The hormesis principle of neuroplasticity and neuroprotection

Animals live in habitats fraught with a range of environmental challenges to their bodies and brains. Accordingly, cells and organ systems have evolved stress-responsive signaling pathways that enable them to not only withstand environmental challenges but also to prepare for future challenges and function more efficiently. These phylogenetically conserved processes are the foundation of the hormesis principle, in which single or repeated exposures to low levels of environmental challenges improve cellular and organismal fitness and raise the probability of survival. Hormetic principles have been most intensively studied in physical exercise but apply to numerous other challenges known to improve human health (e.g., intermittent fasting, cognitive stimulation, and dietary phytochemicals). Here we review the physiological mechanisms underlying hormesis-based neuroplasticity and neuroprotection. Approaching natural resilience from the lens of hormesis may reveal novel methods for optimizing brain function and lowering the burden of neurological disorders.

The role of aging and brain-derived neurotrophic factor signaling in expression of base excision repair genes in the human brain

DNA damage is a central contributor to the aging process. In the brain, a major threat to the DNA is the considerable amount of reactive oxygen species produced, which can inflict oxidative DNA damage. This type of damage is removed by the base excision repair (BER) pathway, an essential DNA repair mechanism, which contributes to genome stability in the brain. Despite the crucial role of the BER pathway, insights into how this pathway is affected by aging in the human brain and the underlying regulatory mechanisms are very limited. By microarray analysis of four cortical brain regions from humans aged 20-99 years (n = 57), we show that the expression of core BER genes is largely downregulated during aging across brain regions. Moreover, we find that expression of many BER genes correlates positively with the expression of the neurotrophin brain-derived neurotrophic factor (BDNF) in the human brain. In line with this, we identify binding sites for the BDNF-activated transcription factor, cyclic-AMP response element-binding protein (CREB), in the promoter of most BER genes and confirm the ability of BDNF to regulate several BER genes by BDNF treatment of mouse primary hippocampal neurons. Together, these findings uncover the transcriptional landscape of BER genes during aging of the brain and suggest BDNF as an important regulator of BER in the human brain.

Docosahexaenoic acid enhances hippocampal insulin sensitivity to promote cognitive function of aged rats on a high-fat diet

INTRODUCTION

Diminished brain insulin sensitivity is associated with reduced cognitive function. Docosahexaenoic acid (DHA) is known to maintain normal brain function.

OBJECTIVES

This study aimed to determine whether DHA impacts hippocampal insulin sensitivity and cognitive function in aged rats fed a high-fat diet (HFD).

METHODS

Eight-month-old female Sprague-Dawley rats were randomly divided into three groups (n = 50 each). Rats in the aged group, HFD group, and DHA treatment group received standard diet (10 kcal% fat), HFD (45 kcal% fat), and DHA-enriched HFD (45 kcal% fat, 1% DHA, W/W) for 10 months, respectively. Four-month-old female rats (n = 40) that received a standard diet served as young controls. Neuroinflammation, oxidative stress, amyloid formation, and tau phosphorylation in the hippocampus, as well as systemic glucose homeostasis and cognitive function, were tested.

RESULTS

DHA treatment relieved a block in the insulin signaling pathway and consequently protected aged rats against HFD-induced hippocampal insulin resistance. The beneficial effects were explained by a DHA-induced decrease in systemic glucose homeostasis dysregulation, hippocampal neuroinflammation and oxidative stress. In addition, DHA treatment broke the reciprocal cycle of hippocampal insulin resistance, Aβ burden, and tau hyperphosphorylation. Importantly, treatment of model rats with DHA significantly increased their cognitive capacity, as evidenced by their increased hippocampal-dependent learning and memory, restored neuron morphology, enhanced cholinergic activity, and activated cyclic AMP-response element-binding protein.

CONCLUSION

DHA improves cognitive function by enhancing hippocampal insulin sensitivity.

Neuroprotective Effects of Neuropeptide Y against Neurodegenerative Disease

Neuropeptide Y (NPY), a 36 amino acid peptide, is widely expressed in the mammalian brain. Changes in NPY levels in different brain regions and plasma have been described in several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic Lateral Sclerosis, and Machado-Joseph disease. The changes in NPY levels may reflect the attempt to set up an endogenous neuroprotective mechanism to counteract the degenerative process. Accumulating evidence indicates that NPY can function as an anti-apoptotic, anti-inflammatory, and pro-phagocytic agent, which may be used effectively to halt or to slow down the progression of the disease. In this review, we will focus on the neuroprotective roles of NPY in several neuropathological conditions, with a particular focus on the anti-inflammatory properties of NPY.

Mitochondria, energy, and metabolism in neuronal health and disease

Mitochondria are associated with various cellular activities critical to homeostasis, particularly in the nervous system. The plastic architecture of the mitochondrial network and its dynamic structure play crucial roles in ensuring that varying energetic demands are rapidly met to maintain neuronal and axonal energy homeostasis. Recent evidence associates ageing and neurodegeneration with anomalous neuronal metabolism, as age-dependent alterations of neuronal metabolism are now believed to occur prior to neurodegeneration. The brain has a high energy demand, which makes it particularly sensitive to mitochondrial dysfunction. Distinct cellular events causing oxidative stress or disruption of metabolism and mitochondrial homeostasis can trigger a neuropathology. This review explores the bioenergetic hypothesis for the neurodegenerative pathomechanisms, discussing factors leading to age-related brain hypometabolism and its contribution to cognitive decline. Recent research on the mitochondrial network in healthy nervous system cells, its response to stress and how it is affected by pathology, as well as current contributions to novel therapeutic approaches will be highlighted.

Healthspan Maintenance and Prevention of Parkinson's-like Phenotypes with Hydroxytyrosol and Oleuropein Aglycone in C. elegans

Numerous studies highlighted the beneficial effects of the Mediterranean diet (MD) in maintaining health, especially during ageing. Even neurodegeneration, which is part of the natural ageing process, as well as the foundation of ageing-related neurodegenerative disorders like Alzheimer’s and Parkinson’s disease (PD), was successfully targeted by MD. In this regard, olive oil and its polyphenolic constituents have received increasing attention in the last years. Thus, this study focuses on two main olive oil polyphenols, hydroxytyrosol (HT) and oleuropein aglycone (OLE), and their effects on ageing symptoms with special attention to PD. In order to avoid long-lasting, expensive, and ethically controversial experiments, the established invertebrate model organism Caenorhabditis elegans was used to test HT and OLE treatments. Interestingly, both polyphenols were able to increase the survival after heat stress, but only HT could prolong the lifespan in unstressed conditions. Furthermore, in aged worms, HT and OLE caused improvements of locomotive behavior and the attenuation of autofluorescence as a marker for ageing. In addition, by using three different C. elegans PD models, HT and OLE were shown i) to enhance locomotion in worms suffering from α-synuclein-expression in muscles or rotenone exposure, ii) to reduce α-synuclein accumulation in muscles cells, and iii) to prevent neurodegeneration in α-synuclein-containing dopaminergic neurons. Hormesis, antioxidative capacities and an activity-boost of the proteasome & phase II detoxifying enzymes are discussed as potential underlying causes for these beneficial effects. Further biological and medical trials are indicated to assess the full potential of HT and OLE and to uncover their mode of action.

Riluzole Attenuates L-DOPA-Induced Abnormal Involuntary Movements Through Decreasing CREB1 Activity: Insights from a Rat Model

Chronic administration of L-DOPA, the first-line treatment of dystonic symptoms in childhood or in Parkinson's disease, often leads to the development of abnormal involuntary movements (AIMs), which represent an important clinical problem. Although it is known that Riluzole attenuates L-DOPA-induced AIMs, the molecular mechanisms underlying this effect are not understood. Therefore, we studied the behavior and performed RNA sequencing of the striatum in three groups of rats that all received a unilateral lesion with 6-hydroxydopamine in their medial forebrain bundle, followed by the administration of saline, L-DOPA, or L-DOPA combined with Riluzole. First, we provide evidence that Riluzole attenuates AIMs in this rat model. Subsequently, analysis of the transcriptomics data revealed that Riluzole is predicted to reduce the activity of CREB1, a transcription factor that regulates the expression of multiple proteins that interact in a molecular landscape involved in apoptosis. Although this mechanism underlying the beneficial effect of Riluzole on AIMs needs to be confirmed, it provides clues towards novel or existing compounds for the treatment of AIMs that modulate the activity of CREB1 and, hence, its downstream targets.

Regulation of fear extinction by long-term depression: The roles of endocannabinoids and brain derived neurotrophic factor

The extinction of a conditioned fear response is of great interest in the search for a means of ameliorating adverse neurobiological changes resulting from stress. The discovery that endocannibinoid (EC) levels are inversely related to the extent of such stress, and that the amygdala is a primary site mediating stress, suggests that ECs in this brain region might play a major role in extinction. Supporting this are the observations that the basolateral complex of the amygdala shows an increase in ECs only during extinction and that early clinical trials indicate that cannabinoid-like agents, when taken orally by patients suffering from post traumatic stress disorder (PTSD), reduce insomnia and nightmares. In order to optimize the potential of these agents to ameliorate symptoms of PTSD four important questions need to be answered: first, what is the identity of the cells that release ECs in the amygdala during extinction; second, what are their sites of action; third, what roles do the ECs play in the alleviation of long- depression (LTD), a process central to extinction; and finally, to what extent does brain derived neurotrophic factor (BDNF) facilitate the release of ECs? A review of the relevant literature is presented in an attempt to answer these questions. It is suggested that the principal cell involved in EC synthesis and release during extinction is the so-called excitatory extinction neuron in the basal nucleus of the amygdala. Furthermore that the main site of action of the ECs is the adjacent calcitonin gene-related peptide inhibitory interneurons, whose normal role of blocking the excitatory neurons is greatly diminished. The molecular pathways leading (during extinction trials) to the synthesis and release of ECs from synaptic spines of extinction neurons, that is potentiated by BDNF, are also delineated in this review. Finally, consideration is given to how the autocrine action of BDNF, linked to the release of ECs, can lead to the sustained release of these, so maintaining extinction over long times.

Unexpected effects of sublethal doses of insecticide on the peripheral olfactory response and sexual behavior in a pest insect

Pesticides have long been used as the main solution to limit agricultural pests, but their widespread use resulted in chronic or diffuse environmental pollutions, development of insect resistances, and biodiversity reduction. The effects of low residual doses of these chemical products on organisms that affect both targeted species (crop pests) but also beneficial insects became a major concern, particularly because low doses of pesticides can induce unexpected positive--also called hermetic--effects on insects, leading to surges in pest population growth at greater rate than what would have been observed without pesticide application. The present study aimed to examine the effects of sublethal doses of deltamethrin, one of the most used synthetic pyrethroids, known to present a residual activity and persistence in the environment, on the peripheral olfactory system and sexual behavior of a major pest insect, the cotton leafworm Spodoptera littoralis. We highlighted here a hormetic effect of sublethal dose of deltamethrin on the male responses to sex pheromone, without any modification of their response to host-plant odorants. We also identified several antennal actors potentially involved in this hormetic effect and in the antennal detoxification or antennal stress response of/to deltamethrin exposure.

Low dose Hsp90 inhibitor 17AAG protects neural progenitor cells from ischemia induced death

Stress adaptation effect provides cell protection against ischemia induced apoptosis. Whether this mechanism prevents other types of cell death in stroke is not well studied. This is an important question for regenerative medicine to treat stroke since other types of cell death such as necrosis are also prominent in the stroke brain apart from apoptosis. We report here that treatment with 17-N-Allylamino-17-demethoxygeldanamycin (17AAG), an Hsp90 inhibitor, protected neural progenitor cells (NPCs) against oxygen glucose deprivation (OGD) induced cell death in a dose dependent fashion. Cell death assays indicated that 17AAG not only ameliorated apoptosis, but also necrosis mediated by OGD. This NPC protection was confirmed by exposing cells to oxidative stress, a major stress signal prevalent in the stroke brain. Mechanistic studies demonstrated that 17AAG activated PI3K/Akt and MAPK cell protective pathways. More interestingly, these two pathways were activated in vivo by 17AAG and 17AAG treatment reduced infarct volume in a middle cerebral artery occlusion (MCAO) stroke model. These data suggest that 17AAG protects cells against major cell death pathways and thus might be used as a pharmacological conditioning agent for regenerative medicine for stroke.

BDNF and exercise enhance neuronal DNA repair by stimulating CREB-mediated production of apurinic/apyrimidinic endonuclease 1

Brain-derived neurotrophic factor (BDNF) promotes the survival and growth of neurons during brain development and mediates activity-dependent synaptic plasticity and associated learning and memory in the adult. BDNF levels are reduced in brain regions affected in Alzheimer's, Parkinson's, and Huntington's diseases, and elevation of BDNF levels can ameliorate neuronal dysfunction and degeneration in experimental models of these diseases. Because neurons accumulate oxidative lesions in their DNA during normal activity and in neurodegenerative disorders, we determined whether and how BDNF affects the ability of neurons to cope with oxidative DNA damage. We found that BDNF protects cerebral cortical neurons against oxidative DNA damage-induced death by a mechanism involving enhanced DNA repair. BDNF stimulates DNA repair by activating cyclic AMP response element-binding protein (CREB), which, in turn, induces the expression of apurinic/apyrimidinic endonuclease 1 (APE1), a key enzyme in the base excision DNA repair pathway. Suppression of either APE1 or TrkB by RNA interference abolishes the ability of BDNF to protect neurons against oxidized DNA damage-induced death. The ability of BDNF to activate CREB and upregulate APE1 expression is abolished by shRNA of TrkB as well as inhibitors of TrkB, PI3 kinase, and Akt kinase. Voluntary running wheel exercise significantly increases levels of BDNF, activates CREB, and upregulates APE1 in the cerebral cortex and hippocampus of mice, suggesting a novel mechanism whereby exercise may protect neurons from oxidative DNA damage. Our findings reveal a previously unknown ability of BDNF to enhance DNA repair by inducing the expression of the DNA repair enzyme APE1.

Possible role of NF-κB in hormesis during ageing

Hormesis in ageing is probably represented by mild stress-induced stimulation of protective mechanisms in cells and organisms resulting in biologically beneficial effects. Mild stress and hormetins may act on bifurcation points in the complex network of cell signaling and transcription factors, often turning homeodynamics to health or survival. Several signaling pathways activated by diverse stimuli and by stress response converge on NF-κB activation, resulting in a regulatory system characterized by high complexity. NF-κB behaves as a chaotic oscillator and it is increasingly recognized that the number of components that impinges upon phenotypic outcomes of signal transduction pathways may be higher than those taken into consideration from canonical pathway representations. NF-κB is closely related to other important upstream signaling networks, creating chaotic oscillators with other receptor-related kinases and targeting hubs for hormesis. The great bulk of natural hormetins acts on these signaling pathways, while NF-κB appears as a key regulatory factor in this context. Due to its tight relationship with main signaling system NF-κB plays a fundamental role in stress response, apoptosis and autophagy and appears to be a possible target for hormesis in ageing.

Ghrelin-attenuated cognitive dysfunction in streptozotocin-induced diabetic rats

Diabetic encephalopathy is clinically characterized by acquired behavior and cognitive dysfunction but its pathogenesis is not clear. This study aimed to explore the pathogenesis of diabetic encephalopathy and the mechanisms of ghrelin to ameliorate cognitive dysfunction in diabetic rats. Thirty-six streptozotocin diabetic rat models were established; 12 weeks later, all the rats were randomly divided into 3 groups [diabetic model group (D), ghrelin treatment group (T1), and ghrelin and D-lys-3-GHRP-6 treatment group (T2)] of 12 each. Twelve normoglycemic rats were classified in the normal group (N). Learning and memory behaviors were measured using a spatial version of the Morris water maze test. The brain-derived neurotrophic factor (BDNF), cAMP responsive element binding protein (CREB), phosphorylated CREB (p-CREB), phosphorylated ERK1/2 (p-ERK1/2), caspase-3, and Bcl-xl protein expressions in the hippocampi of all the rats were detected using immunohistochemistry. The mRNA expressions of BDNF, CREB, and caspase-3 were examined using reverse transcription-polymerase chain reaction. The hippocampus neuronal apoptosis was measured by terminal deoxynucleotidyl transferase dUTP nick end labeling method. We found that learning and memory level in the ghrelin treatment group improved significantly, expression of Bcl-xl, BDNF, CREB, p-CREB, and p-ERK1/2 in the hippocampus was increased in the ghrelin treatment group, and the number of apoptotic neurons in the hippocampus decreased remarkably. Our results showed that the changes of BDNF, CREB, and hippocampus neuronal apoptosis might be involved in the pathogenesis of diabetic encephalopathy. We suggested that ghrelin improved cognitive ability in streptozotocin-induced diabetic rats by improving the expressions of BDNF and CREB and by attenuating hippocampus neuronal apoptosis. The effects of ghrelin depend on the receptor of ghrelin, GHSR-1a, and ERK1/2 pathway.

Hormesis, cell death, and regenerative medicine for neurode-generative diseases

Although the adult human brain has a small number of neural stem cells, they are insufficient to repair the damaged brain to achieve significant functional recovery for neurodegenerative diseases and stroke. Stem cell therapy, by either enhancing endogenous neurogenesis, or transplanting stem cells, has been regarded as a promising solution. However, the harsh environment of the diseased brain posts a severe threat to the survival and correct differentiation of those new stem cells. Hormesis (or preconditioning, stress adaptation) is an adaptation mechanism by which cells or organisms are potentiated to survive an otherwise lethal condition, such as the harsh oxidative stress in the stroke brain. Stem cells treated by low levels of chemical, physical, or pharmacological stimuli have been shown to survive better in the neurodegenerative brain. Thus combining hormesis and stem cell therapy might improve the outcome for treatment of these diseases. In addition, since the cell death patterns and their underlying molecular mechanism may vary in different neurodegenerative diseases, even in different progression stages of the same disease, it is essential to design a suitable and optimum hormetic strategy that is tailored to the individual patient.

Aspirin regulates SNARE protein expression and phagocytosis in dendritic cells

Since being introduced globally as Aspirin in 1899, acetylsalicylic acid (ASA) has been widely used as an analgesic, immune-regulatory, anti-pyretic and anti-thrombotic drug. ASA and its metabolite, salicylate, were also reported to be able to modulate antigen presenting functions of dendritic cells (DC). However, the intracellular targets of ASA in DC are still poorly understood. Since phagocytosis is the initial step taken by antigen-presenting cells in the uptake of antigens for processing and presentation, ASA might exerts its immune-regulatory effects by regulating phagocytosis. Here we show that ASA inhibits phagocytosis and modulates expression of endosomal SNAREs, such as Vti1a, Vti1b, VAMP-3, VAMP-8 and Syn-8 (but not syn-6 and syn-16) in DC. We further show that the phagocytic inhibitory effect of ASA is dependent on the expression of Vti1a and Vti1b. Consistently, Vti1a and Vti1b localize to the phagosomes and up-regulation of Vti1a and Vti1b inhibits phagocytosis in DC. Our results suggest that ASA modulates phagocytosis in part through the control of endosomal SNARE protein expression and localization in DC. All experiments were performed using either a murine DC line (DC2.4) or primary DC derived from murine bone marrow cells.

Effects of estrogen on beta-amyloid-induced cholinergic cell death in the nucleus basalis magnocellularis

Alzheimer disease is characterized by accumulation of β-amyloid (Aβ) and cognitive dysfunctions linked to early loss of cholinergic neurons. As estrogen-based hormone replacement therapy has beneficial effects on cognition of demented patients, and it may prevent memory impairments, we investigated the effect of estrogen-pretreatment on Aβ-induced cholinergic neurodegeneration in the nucleus basalis magnocellularis (NBM). We tested which Aβ species induces the more pronounced cholinotoxic effect in vivo. We injected different Aβ assemblies in the NBM of mice, and measured cholinergic cell and cortical fiber loss. Spherical Aβ oligomers had the most toxic effect. Pretreatment of ovariectomized mice with estrogen before Aβ injection decreased cholinergic neuron loss and partly prevented fiber degeneration. By using proteomics, we searched for proteins involved in estrogen-mediated protection and in Aβ toxicity 24 h following injection. The change in expression of, e.g., DJ-1, NADH ubiquinone oxidoreductase, ATP synthase, phosphatidylethanolamine-binding protein 1, protein phosphatase 2A and dimethylarginine dimethylaminohydrolase 1 support our hypothesis that Aβ induces mitochondrial dysfunction, decreases MAPK signaling, and increases NOS activation in NBM. On the other hand, altered expression of, e.g., MAP kinase kinase 1 and 2, protein phosphatase 1 and 2A by Aβ might increase MAPK suppression and NOS signaling in the cortical target area. Estrogen pretreatment reversed most of the changes in the proteome in both areas. Our experiments suggest that regulation of the MAPK pathway, mitochondrial pH and NO production may all contribute to Aβ toxicity, and their regulation can be prevented partly by estrogen pretreatment.

Learning induces neurotrophin signaling at hippocampal synapses

Learning-induced trophic activity is thought to be critical for maintaining health of the aging brain. We report here that learning, acting through an unexpected pathway, activates synaptic receptors for one of the brain's primary trophic factors. Unsupervised learning, but not exploratory activity alone, robustly increased the number of postsynaptic densities associated with activated (phosphorylated) forms of BDNF's TrkB receptor in adult rat hippocampus; these increases were blocked by an NMDA receptor antagonist. Similarly, stimulation of hippocampal slices at the learning-related theta frequency increased synaptic TrkB phosphorylation in an NMDA receptor-dependent fashion. Theta burst stimulation, which was more effective in this regard than other stimulation patterns, preferentially engaged NMDA receptors that, in turn, activated Src kinases. Blocking the latter, or scavenging extracellular TrkB ligands, prevented theta-induced TrkB phosphorylation. Thus, synaptic TrkB activation was dependent upon both ligand presentation and postsynaptic signaling cascades. These results show that afferent activity patterns and cellular events involved in memory encoding initiate BDNF signaling through synaptic TrkB, thereby ensuring that learning will trigger neurotrophic support.

Stress to the rescue: is hormesis a 'cure' for aging?

Despite the fact that the phenomenon of hormesis has been known for many years it is still very much an area of controversy just how useful hormetic treatments are in preventing age-related human diseases and increasing life expectancy. Since there are no data in humans demonstrating hormesis as an effective anti-ageing strategy we turn to a simple model organism for insight. In this review we explore what can be predicted about the usefulness of hormetic treatments in humans based upon studies conducted in the soil nematode Caenorhabditis elegans.

Plant adaptogens increase lifespan and stress resistance in C. elegans

Extracts of plant adaptogens such as Eleutherococcus senticosus (or Acanthopanax senticosus) and Rhodiola rosea can increase stress resistance in several model systems. We now show that both extracts also increase the mean lifespan of the nematode C. elegans in a dose-dependent way. In at least four independent experiments, 250 microg/ml Eleutherococcus (SHE-3) and 10-25 microg/ml Rhodiola (SHR-5) significantly increased life span between 10 and 20% (P < 0.001), increased the maximum lifespan with 2-3 days and postponed the moment when the first individuals in a population die, suggesting a modulation of the ageing process. With higher concentrations, less effect was observed, whereas at the highest concentrations tested (2500 microg/ml Eleutherococcus and 250 microg/ml Rhodiola) a lifespan shortening effect was observed of 15-25% (P < 0.001). Both adaptogen extracts were also able to increase stress resistance in C. elegans: against a relatively short heat shock (35 degrees C during 3 h) as well as chronic heat treatment at 26 degrees C. An increase against chronic oxidative stress conditions was observed in mev-1 mutants, and during exposure of the wild type nematode to paraquat (10 mM) or UV stress, be it less efficiently. Concerning the mode of action: both adaptogens induce translocation of the DAF-16 transcription factor from the cytoplasm into the nucleus, suggesting a reprogramming of transcriptional activities favoring the synthesis of proteins involved in stress resistance (such as the chaperone HSP-16) and longevity. Based on these observations, it is suggested that adaptogens are experienced as mild stressors at the lifespan-enhancing concentrations and thereby induce increased stress resistance and a longer lifespan.

Hormesis defined

Hormesis is a term used by toxicologists to refer to a biphasic dose-response to an environmental agent characterized by a low dose stimulation or beneficial effect and a high dose inhibitory or toxic effect. In the fields of biology and medicine hormesis is defined as an adaptive response of cells and organisms to a moderate (usually intermittent) stress. Examples include ischemic preconditioning, exercise, dietary energy restriction and exposures to low doses of certain phytochemicals. Recent findings have elucidated the cellular signaling pathways and molecular mechanisms that mediate hormetic responses which typically involve enzymes such as kinases and deacetylases, and transcription factors such as Nrf-2 and NF-kappaB. As a result, cells increase their production of cytoprotective and restorative proteins including growth factors, phase 2 and antioxidant enzymes, and protein chaperones. A better understanding of hormesis mechanisms at the cellular and molecular levels is leading to and to novel approaches for the prevention and treatment of many different diseases.