Epigenetic and Proteomic Expression Changes Promoted by Eating Addictive-Like Behavior.

An increasing perspective conceptualizes obesity and overeating as disorders related to addictive-like processes that could share common neurobiological mechanisms. In the present study, we aimed at validating an animal model of eating addictive-like behavior in mice, based on the DSM-5 substance use disorder criteria, using operant conditioning maintained by highly palatable chocolate-flavored pellets. For this purpose, we evaluated persistence of food-seeking during a period of non-availability of food, motivation for food, and perseverance of responding when the reward was associated with a punishment. This model has allowed identifying extreme subpopulations of mice related to addictive-like behavior. We investigated in these subpopulations the epigenetic and proteomic changes. A significant decrease in DNA methylation of CNR1 gene promoter was revealed in the prefrontal cortex of addict-like mice, which was associated with an upregulation of CB1 protein expression in the same brain area. The pharmacological blockade (rimonabant 3 mg/kg; i.p.) of CB1 receptor during the late training period reduced the percentage of mice that accomplished addiction criteria, which is in agreement with the reduced performance of CB1 knockout mice in this operant training. Proteomic studies have identified proteins differentially expressed in mice vulnerable or not to addictive-like behavior in the hippocampus, striatum, and prefrontal cortex. These changes included proteins involved in impulsivity-like behavior, synaptic plasticity, and cannabinoid signaling modulation, such as alpha-synuclein, phosphatase 1-alpha, doublecortin-like kinase 2, and diacylglycerol kinase zeta, and were validated by immunoblotting. This model provides an excellent tool to investigate the neurobiological substrate underlying the vulnerability to develop eating addictive-like behavior.

Frustrated expected reward induces differential transcriptional changes in the mouse brain.

Frustration represents a particular aspect of the addictive process that is related to loss of control when the expected reward is not obtained. We aim to study the consequences of frustrated expected reward on gene expression in the mouse brain. For this purpose, we used an operant model of frustration using palatable food as reward combined with microarrays. Transcriptomic profiles of frontal cortex, ventral striatum and hippocampus were analysed in five groups of mice: (1) positive control receiving palatable food and the cue light as conditioned stimulus; (2) frustrated group only receiving the cue light; (3) extinction learning group that did not receive palatable food nor the light; (4) negative control that never received the reinforcer nor the light during the whole experiment; and (5) yoked that received palatable food passively. Gene expression changes produced by frustration were revealed in the frontal cortex and ventral striatum, but not in the hippocampus. Most of the changes, such as the modification of the dopamine-DARPP-32 signalling pathway, were common in both areas and estimated to have neuronal origin. Extinction learning induced transcriptional changes only in the ventral striatum, with most genes showing down-regulation and without alteration in the dopamine-DARPP-32 signalling pathway. Active palatable food-seeking behaviour induced changes in gene expression in ventral striatum mainly affecting cell communication. In conclusion, frustration behaviour-induced changes in frontal cortex and ventral striatum mainly related to dopamine-DARPP-32 signalling that could play an important role in the loss of behavioural control during the addictive processes.

Human N-methyl D-aspartate receptor antibodies alter memory and behaviour in mice.

Anti-N-methyl D-aspartate receptor (NMDAR) encephalitis is a severe neuropsychiatric disorder that associates with prominent memory and behavioural deficits. Patients' antibodies react with the N-terminal domain of the GluN1 (previously known as NR1) subunit of NMDAR causing in cultured neurons a selective and reversible internalization of cell-surface receptors. These effects and the frequent response to immunotherapy have suggested an antibody-mediated pathogenesis, but to date there is no animal model showing that patients' antibodies cause memory and behavioural deficits. To develop such a model, C57BL6/J mice underwent placement of ventricular catheters connected to osmotic pumps that delivered a continuous infusion of patients' or control cerebrospinal fluid (flow rate 0.25 µl/h, 14 days). During and after the infusion period standardized tests were applied, including tasks to assess memory (novel object recognition in open field and V-maze paradigms), anhedonic behaviours (sucrose preference test), depressive-like behaviours (tail suspension, forced swimming tests), anxiety (black and white, elevated plus maze tests), aggressiveness (resident-intruder test), and locomotor activity (horizontal and vertical). Animals sacrificed at Days 5, 13, 18, 26 and 46 were examined for brain-bound antibodies and the antibody effects on total and synaptic NMDAR clusters and protein concentration using confocal microscopy and immunoblot analysis. These experiments showed that animals infused with patients' cerebrospinal fluid, but not control cerebrospinal fluid, developed progressive memory deficits, and anhedonic and depressive-like behaviours, without affecting other behavioural or locomotor tasks. Memory deficits gradually worsened until Day 18 (4 days after the infusion stopped) and all symptoms resolved over the next week. Accompanying brain tissue studies showed progressive increase of brain-bound human antibodies, predominantly in the hippocampus (maximal on Days 13-18), that after acid extraction and characterization with GluN1-expressing human embryonic kidney cells were confirmed to be against the NMDAR. Confocal microscopy and immunoblot analysis of the hippocampus showed progressive decrease of the density of total and synaptic NMDAR clusters and total NMDAR protein concentration (maximal on Day 18), without affecting the post-synaptic density protein 95 (PSD95) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. These effects occurred in parallel with memory and other behavioural deficits and gradually improved after Day 18, with reversibility of symptoms accompanied by a decrease of brain-bound antibodies and restoration of NMDAR levels. Overall, these findings establish a link between memory and behavioural deficits and antibody-mediated reduction of NMDAR, provide the biological basis by which removal of antibodies and antibody-producing cells improve neurological function, and offer a model for testing experimental therapies in this and similar disorders.

Effects of genetic deletion of endogenous opioid system components on the reinstatement of cocaine-seeking behavior in mice.

The repeated cycles of cessation of consumption and relapse remain the major clinical concern in treating drug addiction. The endogenous opioid system is a crucial component of the reward circuit that participates in the adaptive changes leading to relapse in the addictive processes. We have used genetically modified mice to evaluate the involvement of µ-opioid receptor (MOR) and δ-opioid receptor (DOR) and their main endogenous ligands, the enkephalins derived from proenkephalin (PENK) and prodynorphin (PDYN), in the reinstatement of cocaine-seeking behavior. Constitutive knockout mice of MOR, DOR, PENK, and PDYN, and their wild-type littermates were trained to self-administer cocaine or to seek for palatable food, followed by a period of extinction and finally tested on a cue-induced reinstatement of seeking behavior. The four lines of knockout mice acquired operant cocaine self-administration behavior, although DOR and PENK knockout mice showed less motivation for cocaine than wild-type littermates. Moreover, cue-induced relapse was significantly decreased in MOR and DOR knockout mice. In contrast, PDYN knockout mice showed a slower extinction and increased relapse than wild-type littermates. C-Fos expression analysis revealed differential activation in brain areas related with memory and reward in these knockout mice. No differences were found in any of the four genotypes in operant responding to obtain palatable food, indicating that the changes revealed in knockout mice were not due to unspecific deficit in operant performance. Our results indicate that MOR, DOR, and PDYN have a differential role in cue-induced reinstatement of cocaine-seeking behavior.

Relationships between serotonergic and cannabinoid system in depressive-like behavior: a PET study with [11C]-DASB.

Chronic stress represents a major environmental risk factor for mood disorders in vulnerable individuals. The neurobiological mechanisms underlying these disorders involve serotonergic and endocannabinoid systems. In this study, we have investigated the relationships between these two neurochemical systems in emotional control using genetic and imaging tools. CB1 cannabinoid receptor knockout mice (KO) and wild-type littermates (WT) were exposed to chronic restraint stress. Depressive-like symptoms (anhedonia and helplessness) were produced by chronic stress exposure in WT mice. CB1 KO mice already showed these depressive-like manifestations in non-stress conditions and the same phenotype was observed after chronic restraint stress. Chronic stress similarly impaired long-term memory in both genotypes. In addition, brain levels of serotonin transporter (5-HTT) were assessed using positron emission tomography. Decreased brain 5-HTT levels were revealed in CB1 KO mice under basal conditions, as well as in WT mice after chronic stress. Our results show that chronic restraint stress induced depressive-like behavioral alterations and brain changes in 5-HTT levels similarly to those revealed in CB1 KO mice in non-stressed conditions. These results underline the relevance of chronic environmental stress on serotonergic and endocannabinoid transmission for the development of depressive symptoms. Chronic restraint stress induces depressive-like behavior and reduced 5-HTT levels in WT mice similar to those revealed in non-stressed CB1-KO mice. Reduced 5-HTT in both genotypes increases synaptic 5-HT concentration. The 5-HT release is modulated through CB1 receptors and the absence of inhibitory CB1 receptor causes decreased inhibition of 5-HT release resulting in high synaptic 5-HT concentration that are not further enhanced by stress.

Intrathecal injection of P/Q type voltage-gated calcium channel antibodies from paraneoplastic cerebellar degeneration cause ataxia in mice.

The role of antibodies against the P/Q type voltage-gated calcium channels (VGCC-ab) in the pathogenesis of paraneoplastic cerebellar degeneration (PCD) and lung cancer is unclear. We evaluated in mice the effect of intrathecal injection of IgG purified from serum of a patient with both PCD and Lambert-Eaton myasthenic syndrome (LEMS), and from another patient with isolated LEMS. Mice injected with PCD/LEMS IgG developed marked, reversible ataxia compared with those injected with LEMS or control IgG. These findings suggest that P/Q-type VGCC-ab may play a role in the pathogenesis of ataxia in patients with PCD and SCLC.

Neuronal cell cycle re-entry markers are altered in the senescence accelerated mouse P8 (SAMP8).

Senescence-accelerated mice 8 (SAMP8), a model of aging, display many established pathological features of Alzheimer's disease (AD); however, whether cell cycle alterations exist in these animals remains unknown. Given that these animals present changes such as tau phosphorylation and redox imbalance, both associated with cell cycle alterations, we determined whether changes in cell cycle markers were present in SAMP8 and SAMR1 (control strain) at 3, 6, and 9 months-old brains. As expected, an increase in tau hyperphosphorylation and its associated machinery, i.e., cdk5 and GSK3ß, was observed both between strains and also with aging. Particularly, significant differences in cyclin A, cyclin D1, cyclin E, Cdk2, cyclin B, pR, and E2F1 were found when comparing SAMP8 to SAMR1. More interestingly, a partial correlation with several cell cycle markers described in AD brain is found in SAMP8, indicating that some specific hallmarks of AD are also present in this strain, which has been postulated as an early switch model of the disease.

Operant model of frustrated expected reward in mice.

One aspect of the addictive process that has not been thoroughly investigated is the consequence of the frustrated state occurring when the drug is not available. The present study aimed to validate a novel operant model of frustrated expected reward in mice. C57BL/6J mice were trained in operant conditioning maintained by chocolate-flavoured pellets or cocaine. After the completion of high rates of responding on a progressive ratio schedule, the reward was unexpectedly withheld. The consequences of this frustrated behaviour on anxiety, aggressiveness, perseveration, extinction and reinstatement were investigated. Mice exposed to the frustrated event perseverated in the operant responses and showed increased aggressiveness in the resident-intruder test. These animals also showed higher rates of cue-induced reinstatement of drug seeking. The present study provides a reliable operant model in mice to evaluate a frustrated state following reward unavailability. This animal model could be useful to study the behavioural and neurochemical consequences related to the emotional states generated during the omission of a highly expected reward.

Efectos de la melatonina en el cerebro de ratones con senescencia acelerada SAMP8 / Effects of melatonin in the brain of the senescence-accelerated mice-prone 8 (SAMP8) model

Los ratones con senescencia acelerada (SAM) son un modelo de envejecimiento establecido por selección fenotípica a partir de la cepa de ratones AKR/J. La cepa SAMP8 es un buen modelo animal para investigar los mecanismos fundamentales, tanto genéticos como proteicos, del envejecimiento, fisiológico y patológico, ya que estos ratones presentan marcadores específicos de trastornos neurodegenerativos, como la enfermedad de Alzheimer. La melatonina es conocida como la hormona del sueño, ya que se encarga de controlar los ciclos de sueño/vigilia. Además, se ha observado que es un potente antioxidante, y que podría tener un importante efecto antienvejecimiento. El tratamiento crónico con melatonina modula el estrés oxidativo, así como la vía de calpaína/Cdk5, GSK3beta y la fosforilación de tau en cerebros de ratones SAMP8, revelando el efecto antienvejecimiento y neuroprotector de esta hormona (AU)

Senescence-accelerated mice (SAM) represent an aging model establish by selective inbreeding of the AKR/J strain. SAMP8 is a suitable model to study the genetics or proteics fundamental mechanisms of aging, in physiological or pathological conditions, because SAMP8 develop neuropathological markers also found in neurodegenerative diseases like Alzheimer. Melatonin is known as sleep hormone because its action controlling the sleep/awake circadian rhythm. Moreover, melatonin has antioxidant properties and may have an important anti-aging role. The chronic treatment with melatonin in the SAMP8 model was able to reduce oxidative stress and the neurodegenerative calpain/Cdk5 pathway and primed phosphorylation of GSK3beta and tau hiperphosphorylation markers of cerebral aging and neurodegeneration in SAMP8 brains, indicating the neuroprotective and anti-aging effect of melatonin (AU)

Activation of ataxia telangiectasia muted under experimental models and human Parkinson's disease.

In the present study we demonstrated that neurotoxin MPP(+)-induced DNA damage is followed by ataxia telangiectasia muted (ATM) activation either in cerebellar granule cells (CGC) or in B65 cell line. In CGC, the selective ATM inhibitor KU-55933 showed neuroprotective effects against MPP(+)-induced neuronal cell loss and apoptosis, lending support to the key role of ATM in experimental models of Parkinson's disease. Likewise, we showed that knockdown of ATM levels in neuroblastoma B65 cells using an ATM-specific siRNA attenuates the phosphorylation of retinoblastoma protein without affecting other cell-cycle proteins involved in the G(0)/G(1) cell-cycle phase. Moreover, we demonstrated DNA damage, in human brain samples of PD patients. These findings support a model in which MPP(+) leads to ATM activation with a subsequent DNA damage response and activation of pRb. Therefore, this study demonstrates a new link between DNA damage by MPP(+) and cell-cycle re-entry through retinoblastoma protein phosphorylation.

Evaluation of potential pro-survival pathways regulated by melatonin in a murine senescence model.

We examined the effect of melatonin on pro-survival processes in three groups of mice. Untreated senescence-accelerated mice (SAMP8), melatonin-treated SAMP8 and untreated senescence-accelerated resistant mice (SAMR1) of 10 months old were studied. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) was supplied in the drinking water from the end of the first month until the end of the ninth month of life. Differences in the Akt/Erk1-2 pathway and downstream targets were examined and no significant changes were observed, except for beta-catenin. However, sirtuin 1 expression was significantly lower in SAMP8 than in SAMR1. In addition, acetylated p53 and NFkappaB expression were lower in SAMP8 than in SAMR1. These changes were prevented by melatonin. Moreover, the concentration/expression of alpha-secretase was lower and that of amyloid beta aggregates (Abeta) was higher in untreated SAMP8 than in SAMR1. Likewise, the levels of Bid were higher, whereas Bcl-2(XL) levels were lower in SAMP8 than in SAMR1. Melatonin reduced all these changes. We conclude that melatonin improves pro-survival signals and reduces pro-death signals in age-related impairments of neural processes.

Dysfunction of astrocytes in senescence-accelerated mice SAMP8 reduces their neuroprotective capacity.

Early onset increases in oxidative stress and tau pathology are present in the brain of senescence-accelerated mice prone (SAMP8). Astrocytes play an essential role, both in determining the brain's susceptibility to oxidative damage and in protecting neurons. In this study, we examine changes in tau phosphorylation, oxidative stress and glutamate uptake in primary cultures of cortical astrocytes from neonatal SAMP8 mice and senescence-accelerated-resistant mice (SAMR1). We demonstrated an enhancement of abnormally phosphorylated tau in Ser(199) and Ser(396) in SAMP8 astrocytes compared with that of SAMR1 control mice. Gsk3beta and Cdk5 kinase activity, which regulate tau phosphorylation, was also increased in SAMP8 astrocytes. Inhibition of Gsk3beta by lithium or Cdk5 by roscovitine reduced tau phosphorylation at Ser(396). Moreover, we detected an increase in radical superoxide generation, which may be responsible for the corresponding increase in lipoperoxidation and protein oxidation. We also observed a reduced mitochondrial membrane potential in SAMP8 mouse astrocytes. Glutamate uptake in astrocytes is a critical neuroprotective mechanism. SAMP8 astrocytes showed a decreased glutamate uptake compared with those of SAMR1 controls. Interestingly, survival of SAMP8 or SAMR1 neurons cocultured with SAMP8 astrocytes was significantly reduced. Our results indicate that alterations in astrocyte cultures from SAMP8 mice are similar to those detected in whole brains of SAMP8 mice at 1-5 months. Moreover, our findings suggest that this in vitro preparation is suitable for studying the molecular and cellular processes underlying early aging in this murine model. In addition, our study supports the contention that astrocytes play a key role in neurodegeneration during the aging process.

Lithium treatment decreases activities of tau kinases in a murine model of senescence.

Lithium modulates glycogen synthase kinase 3beta (GSK-3beta), a kinase involved in Alzheimer disease-related tau pathology. To investigate mechanisms of aging and the potential therapy of lithium in neurodegenerative disease, we treated senescence-accelerated mouse (SAM)P8 mice, a murine model of senescence, and mice of the control SAMR1 strain with lithium. The treatment reduced hippocampal caspase 3 and calpain activation, indicating that it provides neuroprotection. Lithium also reduced both the levels and activity of GSK-3beta and the activity of cyclin-dependent kinase 5 and reduced hyperphosphorylation of 3 different phosphoepitopes of tau: Ser199, Ser212, and Ser396. In lithium-treated primary cultures of SAMP8 and SAMR1 cerebellar neurons, there was a marked reduction in protease activity mediated by calpain and caspase 3. Both lithium and SB415286, a specific inhibitor of GSK-3beta, reduced apoptosis in vitro. Taken together, these in vivo and in vitro findings of lithium-mediated reductions in GSK-3beta and cyclin-dependent kinase 5 activities, tau phosphorylation, apoptotic activity, and cell death provide a strong rationale for the use of lithium as a potential treatment in neurodegenerative diseases.

Favorable effects of a prolonged treatment with melatonin on the level of oxidative damage and neurodegeneration in senescence-accelerated mice.

Senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) were studied at 5 and 10 months of age, respectively. In the animals, neurodegenerative processes and how they were influenced by melatonin were examined. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) treatments were administrated from the age of 1 to 9 months in the drinking water. Differences in the neurodegenerative markers examined were found between the two strains with a more damaged protein, phosphorylated Tau at Ser392, increased neurofibrillary tangles (NT) and higher alpha-synuclein expression in SAMP8 versus SAMR1 mice overall, when the mice were 10 months of age. Changes in density of receptors and oxidative stress-related signaling with age were found in the brains of SAM strains at 10 months as shown by a marked decrease in the level of MT-1 melatonin receptor and retinoic acid receptor-related orphan receptor (ROR)-alpha1. This diminution was earlier and more pronounced in SAMP8 mice. Likewise, the levels of nuclear factor-kappa B (NF-kB) transcriptional factor were higher in SAMP8 mice compared with SAMR1 mice regardless of age confirming the direct role of oxidative stress in the aging process. Treatment with melatonin in SAMP8 and SAMR1 mice reduced the neurodegenerative changes with an increase of ROR-alpha1 levels without an apparent influence in the levels of MT-1 receptor. However, different melatonin effects on NF-kB signaling were observed suggesting that NF-kB could trigger inflammatory processes in a different way, being SAM strain-dependent and associated with age-related oxidative stress levels. The effectiveness of melatonin in improving age-related neural impairments is corroborated.

Modulation of sirtuins: new targets for antiageing.

Aging is characterized by a progressive deterioration of physiological functions and metabolic processes. Healthy aging remains one of the ideals of modern society. In aging and in diseases associated with the elderly, such as Alzheimer's or Parkinson's, the loss of cells in vital structures or organs may be related to several factors, among which the production of reactive oxygen species (ROS) by mitochondria is a common denominator, one that leads to DNA damage, apoptosis and death. Although a diet rich in antioxidants seems to offer hope in delaying the onset of unhealthy disorders that accompany aging, no clinical treatment as such has yet been developed and anti-aging drugs are still unavailable. It is well established that reducing food intake (caloric restriction) extends the life-span in a wide range of species. The protein implicated in this protective process is the silent information regulator 2 (SIR2, SIRT1 in mammals), an enzyme that belongs to a nicotinamide adenine dinucleotide (NAD)+-dependent protein deacetylases. SIRs regulate gene silencing, DNA repair, rDNA recombination, and ageing, apart from regulating programmed cell death. In this context, increasing SIRT1 has been found to protect cells against amyloid-beta-induced ROS production and DNA damage, thereby reducing apoptotic death in vitro. Moreover, it has been demonstrated that Alzheimer's and Huntington's disease neurons are rescued by the over-expression of SIRT1, induced by either caloric restriction or administration of resveratrol, a potential activator of this enzyme. The therapeutic use of resveratrol (a polyphenol present in red wines) and other related compounds, which utilize SIRT1 pathway modulators, in treating aging-related brain disorders will be discussed in this review. Provided herein are novel new compound related with resveratrol or sirtinol that are able to modulate sirtuin activity that will be tested to treat and/or prevent a wide variety of diseases including, disorders related to aging or neurodegenerative diseases.

Activation of the calpain/cdk5/p25 pathway in the girus cinguli in Parkinson's disease.

The mechanisms involved in neuronal loss in Parkinson's disease (PD) are not known, although recent studies performed in PD experimental models suggest that cdk5/p25 plays a predominant role. In the present study, we examined the gyrus cinguli of cases with PD and compared them with age-matched controls, and we demonstrated an activation of the calpain/cdk5 pathway. We found an increase in the p25/p35 immunoreactivity ratio and in the expression of transcription factor E2F-1. Our results implicate the cdk5/p25 pathway and re-entry into the cell cycle in the process of neuronal loss in patients with PD.

Chronic administration of melatonin reduces cerebral injury biomarkers in SAMP8.

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

Changes in oxidative stress parameters and neurodegeneration markers in the brain of the senescence-accelerated mice SAMP-8.

The senescence-accelerated strains of mice (SAMP) are well-characterized animal models of senescence. Senescence may be related to enhanced production or defective control of reactive oxygen species, which lead to neuronal damage. Therefore, the activity of various oxidative-stress related enzymes was determined in the cortex of 5 months-old senescence-accelerated mice prone-8 (SAMP-8) of both sexes and compared with senescence-accelerated mice-resistant-1 (SAMR-1). Glutathione reductase and peroxidase activities in SAMP-8 male mice were lower than in male SAMR-1, and a decreased catalase activity was found in both male and female SAMP-8 mice, which correlates with the lower catalase expression found by Western blotting. Nissl staining showed marked loss of neuronal cells in the cerebral cortex of five month-old SAMP-8 mice. SAMP-8 mice also had marked astrogliosis and microgliosis. We also found an increase in caspase-3 and calpain activity in the cortex. In addition, we observed morphological changes in the immunostaining of tau protein in SAMP-8, indicative of a loss of their structural function. Altogether, these results show that, at as early as 5 months of age, SAMP-8 mice have cytological and molecular alterations indicative of neurodegeneration in the cerebral cortex and suggestive of altered control of the production of oxidative species and hyper-activation of calcium-dependent enzymes.

Hyperphosphorylation of microtubule-associated protein tau in senescence-accelerated mouse (SAM).

Tau is a neuronal microtubule-associated protein found predominantly on axons. Tau phosphorylation regulates both normal and pathological functions of this protein. Hyperphosphorylation impairs the microtubule binding function of tau, resulting in the destabilization of microtubules in brain, ultimately leading to the degeneration of the affected neurons. Numerous serine/threonine kinases, including GSK-3beta and Cdk5 can phosphorylate tau. SAMR1 and SAMP8 are murine strains of senescence. We show an increase in hyperphosphorylated forms of tau in SAMP8 (senescent mice) in comparison with resistant strain SAMR1. Moreover, an increase in Cdk5 expression and activation is described but analysis of GSK3beta isoforms failed to show differences in SAMP8 in comparison to age-matched SAMR1. In conclusion, tau hyperphosphorylation occurs in SAMP-8 (early senescent) mice, indicating a link between aging and tau modifications in this murine model.