Dmitry Petrov

Early alterations in energy metabolism in the hippocampus of APPswe/PS1dE9 mouse model of Alzheimer's disease

The present study had focused on the behavioral phenotype and gene expression profile of molecules related to insulin receptor signaling in the hippocampus of 3 and 6 month-old APPswe/PS1dE9 (APP/PS1) transgenic mouse model of Alzheimers disease (AD). Elevated levels of the insoluble Aβ (1-42) were detected in the brain extracts of the transgenic animals as early as 3 months of age, prior to the Aβ plaque formation (pre-plaque stage). By the early plaque stage (6 months) both the soluble and insoluble Aβ (1-40) and Aβ (1-42) peptides were detectable. We studied the expression of genes related to memory function (Arc, Fos), insulin signaling, including insulin receptor (Insr), Irs1 and Irs2, as well as genes involved in insulin growth factor pathways, such as Igf1, Igf2, Igfr and Igfbp2. We also examined the expression and protein levels of key molecules related to energy metabolism (PGC1-α, and AMPK) and mitochondrial functionality (OXPHOS, TFAM, NRF1 and NRF2). 6 month-old APP/PS1 mice demonstrated impaired cognitive ability, were glucose intolerant and showed a significant reduction in hippocampal Insr and Irs2 transcripts. Further observations also suggest alterations in key cellular energy sensors that regulate the activities of a number of metabolic enzymes through phosphorylation, such as a decrease in the Prkaa2 mRNA levels and in the pAMPK (Thr172)/Total APMK ratio. Moreover, mRNA and protein analysis reveals a significant downregulation of genes essential for mitochondrial replication and respiratory function, including PGC-1α in hippocampal extracts of APP/PS1 mice, compared to age-matched wild-type controls at 3 and 6 months of age. Overall, the findings of this study show early alterations in genes involved in insulin and energy metabolism pathways in an APP/PS1 model of AD. These changes affect the activity of key molecules like NRF1 and PGC-1α, which are involved in mitochondrial biogenesis. Our results reinforce the hypothesis that the impairments in both insulin signaling and energy metabolism precede the development of AD amyloidogenesis.

Current Research Therapeutic Strategies for Alzheimer’s Disease Treatment

Alzheimers disease (AD) currently presents one of the biggest healthcare issues in the developed countries. There is no effective treatment capable of slowing down disease progression. In recent years the main focus of research on novel pharmacotherapies was based on the amyloidogenic hypothesis of AD, which posits that the beta amyloid (Aβ) peptide is chiefly responsible for cognitive impairment and neuronal death. The goal of such treatments is (a) to reduce Aβ production through the inhibition of β and γ secretase enzymes and (b) to promote dissolution of existing cerebral Aβ plaques. However, this approach has proven to be only modestly effective. Recent studies suggest an alternative strategy centred on the inhibition of the downstream Aβ signalling, particularly at the synapse. Aβ oligomers may cause aberrant N-methyl-D-aspartate receptor (NMDAR) activation postsynaptically by forming complexes with the cell-surface prion protein (PrPC). PrPC is enriched at the neuronal postsynaptic density, where it interacts with Fyn tyrosine kinase. Fyn activation occurs when Aβ is bound to PrPC-Fyn complex. Fyn causes tyrosine phosphorylation of the NR2B subunit of metabotropic glutamate receptor 5 (mGluR5). Fyn kinase blockers masitinib and saracatinib have proven to be efficacious in treating AD symptoms in experimental mouse models of the disease.

High-fat diet-induced deregulation of hippocampal insulin signaling and mitochondrial homeostasis deficiences contribute to Alzheimer disease pathology in rodents

Global obesity is a pandemic status, estimated to affect over 2 billion people, that has resulted in an enormous strain on healthcare systems worldwide. The situation is compounded by the fact that apart from the direct costs associated with overweight pathology, obesity presents itself with a number of comorbidities, including an increased risk for the development of neurodegenerative disorders. Alzheimer disease (AD), the main cause of senile dementia, is no exception. Spectacular failure of the pharmaceutical industry to come up with effective AD treatment strategies is forcing the broader scientific community to rethink the underlying molecular mechanisms leading to cognitive decline. To this end, the emphasis is once again placed on the experimental animal models of the disease. In the current study, we have focused on the effects of a high-fat diet (HFD) on hippocampal-dependent memory in C57/Bl6 Wild-type (WT) and APPswe/PS1dE9 (APP/PS1) mice, a well-established mouse model of familial AD. Our results indicate that the continuous HFD administration starting at the time of weaning is sufficient to produce β-amyloid-independent, hippocampal-dependent memory deficits measured by a 2-object novel-object recognition test (NOR) in mice as early as 6months of age. Furthermore, the resulting metabolic syndrome appears to have direct effects on brain insulin regulation and mitochondrial function. We have observed pathological changes related to both the proximal and distal insulin signaling pathway in the brains of HFD-fed WT and APP/PS1 mice. These changes are accompanied by a significantly reduced OXPHOS metabolism, suggesting that mitochondria play an important role in hippocampus-dependent memory formation and retention in both the HFD-treated and AD-like rodents at a relatively young age.

Masitinib for the treatment of mild to moderate Alzheimer’s disease

Alzheimer’s disease (AD) is a degenerative neurological disorder that is the most common cause of dementia and disability in older patients. Available treatments are symptomatic in nature and are only sufficient to improve the quality of life of AD patients temporarily. A potential strategy, currently under investigation, is to target cell-signaling pathways associated with neurodegeneration, in order to decrease neuroinflammation, excitotoxicity, and to improve cognitive functions. Current review centers on the role of neuroinflammation and the specific contribution of mast cells to AD pathophysiology. The authors look at masitinib therapy and the evidence presented through preclinical and clinical trials. Dual actions of masitinib as an inhibitor of mast cell–glia axis and a Fyn kinase blocker are discussed in the context of AD pathology. Masitinib is in Phase III clinical trials for the treatment of malignant melanoma, mastocytosis, multiple myeloma, gastrointestinal cancer and pancreatic cancer. It is also in Phase II/III clinical trials for the treatment of multiple sclerosis, rheumatoid arthritis and AD. Additional research is warranted to better investigate the potential effects of masitinib in combination with other drugs employed in AD treatment.

Mavoglurant as a treatment for Parkinson’s disease

Introduction: A major unresolved issue in the Parkinson’s disease (PD) treatment is the development of l-DOPA-induced dyskinesias (LIDs) as a side effect of chronic l-DOPA administration. Currently, LIDs are managed in part by reducing the l-DOPA dose or by the administration of amantadine. However, this treatment is only partially effective. A potential strategy, currently under investigation, is the coadministration of metabotropic glutamate receptor 5 (mGluR5) negative allosteric modulators (NAMs) and l-DOPA; a treatment that results in the improvement of dyskinesia symptoms and that permits reductions in l-DOPA dosage frequency. Areas covered: The authors examine the role of mGluR5 in the pathophysiology of PD and the potential use of mGluR5 NAM as an adjuvant therapy together with a primary treatment with l-DOPA. Specifically, the authors look at the mavoglurant therapy and the evidence presented through preclinical and clinical trials. Expert opinion: Interaction between mGluR5 NAM and l-DOPA is an area of interest in PD research as concomitant treatment results in the improvement of LID symptoms in humans, thus enhancing the patient’s quality of life. However, few months ago, Novartis decided to discontinue clinical trials of mavoglurant for the treatment of LID, due to the lack of efficacy demonstrated in trials NCT01385592 and NCT01491529, although no safety concerns were involved in this decision. Nevertheless, the potential application of mGluR5 antagonists as neuroprotective agents must be considered and further studies are warranted to better investigate their potential.

The role of leptin in the sporadic form of Alzheimer's disease. Interactions with the adipokines amylin, ghrelin and the pituitary hormone prolactin.

Leptin (Lep) is emerging as a pivotal molecule involved in both the early events and the terminal phases of Alzheimers disease (AD). In the canonical pathway, Lep acts as an anorexigenic factor via its effects on hypothalamic nucleus. However, additional functions of Lep in the hippocampus and cortex have been unravelled in recent years. Early events in the sporadic form of AD likely involve cellular level alterations which can have an effect on food intake and metabolism. Thus, AD can be conceivably interpreted as a multiorgan pathology that not only results in a dramatic neuronal loss in brain areas such as the hippocampus and the cortex (ultimately leading to a significant cognitive impairment) but as a disease which also affects body-weight homeostasis. According to this view, body-weight control disruptions are to be expected in both the early- and late-stage AD, concomitant with changes in serum Lep content, alterations in Lep transport across the blood-brain barrier (BBB) and Lep receptor-related signalling abnormalities. Lep is a member of the adipokine family of molecules, while the Lep receptor belongs to the class I cytokine receptors. Since cellular response to adipokine signalling can be either potentiated or diminished as a result of specific ligand-receptor interactions, Lep interactions with other members of the adipokine family including amylin, ghrelin and hormones such as prolactin require further investigation. In this review, we provide a general perspective on the functions of Lep in the brain, with a particular focus on the sporadic AD.

Hypercholesterolemia and neurodegeneration. Comparison of hippocampal phenotypes in LDLr knockout and APPswe/PS1dE9 mice

Previous studies suggest that Alzheimers disease (AD) neurobiology could not be explained solely by an increase in β-amyloid levels. Recently, it has been proposed that alterations in brain cholesterol metabolism may contribute to the pathogenesis of AD. In the present work, we focus on early changes in the hippocampal phenotypes of two mouse models in which cognitive impairments were previously described: a) the hypercholesterolemic LDL receptor knockout (LDLr -/-) and b) the APPswe/PS1dE9 (APP/PS1) transgenic model of familial AD. Our initial analysis, subsequent validation and additional experiments at the mRNA and protein levels demonstrate some parallels between the hippocampal phenotypes of these 2 mouse models, however our data suggest that the molecular mechanisms leading to cognitive decline are distinct in LDLr -/- and APP/PS1 animals. Genes related to cytokine signaling were significantly down-regulated in LDLr -/- mice when compared to both the wild-type and APP/PS1 mice, and these include prostaglandin-endoperoxide synthases 1 and 2 (ptgs1 and 2) and nerve grow factor (ngf). We have also detected reduced expression of genes related to lipid metabolism in LDLr -/- mice: peroxisome proliferator activated receptor gamma (pparg), pro-opiomelanocortin-alpha (pomc) and of protein kinase, AMP-activated, alpha 1 catalytic subunit of AMPK (prkaa1). Our array data also indicate that transcriptional activity of early genes involved in memory process, such as FBJ osteosarcoma oncogene (Fos) and the activity regulated cytoskeletal-associated protein (Arc) gene, are increased in the hippocampus of LDLr -/- mice. Several proteins like insulin degrading enzyme (IDE), PGC-1α, OXPHOS 1, NMDAR1 and cyclic AMP response element binding protein (CREB) are up-regulated in the LDLr -/- mice, while in the APP/PS1 mouse model only OXPHOS complexes 2, 3 and 5 are slightly downregulated. Further studies are necessary to understand the molecular pathways involved in memory loss in hypercholesterolemic LDLr -/- mice.

Adipokine pathways are altered in hippocampus of an experimental mouse model of Alzheimer's disease.

A growing body of evidence suggests that β-amyloid peptides (Aβ) are unlikely to be the only factor involved in Alzheimer’s disease (AD) aetiology. In fact, a strong correlation has been established between AD patients and patients with type 2 diabetes and/or cholesterol metabolism alterations. In addition, a link between adipose tissue metabolism, leptin signalling in particular, and AD has also been demonstrated. In the present study we analyzed the expression of molecules related to metabolism, with the main focus on leptin and prolactin signalling pathways in an APPswe/PS1dE9 (APP/PS1) transgenic mice model, at 3 and 6 months of age, compared to wild-type controls. We have chosen to study 3 months-old APP/PS1 animals at an age when neither the cognitive deficits nor significant Aβ plaques in the brain are present, and to compare them to the 6 months-old mice, which exhibit elevated levels of Aβ in the hippocampus and memory loss. A significant reduction in both mRNA and protein levels of the prolactin receptor (PRL-R) was detected in the hippocampi of 3 months old APP/PS1 mice, with a decrease in the levels of the leptin receptor (OB-R) first becoming evident at 6 months of age. We proceeded to study the expression of the intracellular signalling molecules downstream of these receptors, including stat (1–5), sos1, kras and socs (1–3). Our data suggest a downregulation in some of these molecules such as stat-5b and socs (1–3), in 3 months-old APP/PS1 brains. Likewise, at the same age, we detected a significant reduction in mRNA levels of lrp1 and cyp46a1, both of which are involved in cholesterol homeostasis. Taken together, these results demonstrate a significative impairment in adipokine receptors signalling and cholesterol regulation pathways in the hippocampus of APP/PS1 mice at an early age, prior to the Aβ plaque formation.

Vulnerability of calbindin, calretinin and parvalbumin in a transgenic/knock-in APPswe/PS1dE9 mouse model of Alzheimer disease together with disruption of hippocampal neurogenesis.

The pathogenesis of Alzheimer disease (AD) is characterized by accumulation of β-amyloid protein in the brain (in both soluble and insoluble forms) and by the presence of intracellular neurofibrillary tangles (NFTs), leading to neurotoxicity. The exact mechanisms whereby Aβ triggers brain alterations are unclear. However, accumulating evidence suggests that a deregulation of Ca(2+) signaling may play a major role in disease progression. Calcium-buffering proteins, including calbindin-D28K (CB), calretinin (CR) and parvalbumin (PV), may offer neuroprotection by maintaining calcium homeostasis. Although marked reductions in these proteins have been observed in the brains of mice and humans with AD, their contribution to AD pathology remains unclear. The aim of the present study was to analyze distribution patterns of CB(+,) CR(+) and PV(+) interneurons in different areas of the hippocampus, a brain region that is severely affected in AD. A transgenic knock-in APPswe/PS1dE9 mouse model of familial AD was used. The data were obtained from the brains of 3- and 12-month-old animals. These ages roughly correspond to an early mature adult (prior to clinical manifestations) and a late middle-age (clinical symptoms readily detectable) phase in human AD patients. Immunostaining revealed increases in CB and PV immunoreactivity (IR) in the hippocampus of 3-month-old transgenic mice, compared to wild-type animals. Possibly, these proteins are upregulated in an attempt to control cellular homeostasis and synaptic plasticity. However, the pattern of CB-IR was reversed in 12-month-old animals, potentially indicating a loss of cellular capacity to respond to pathophysiological processes. In addition, at this age, a noticeable increase in PV-IR was observed, suggesting the presence of hippocampal network hyperactivity in older AD-like mice. Our results indicate that CaBP(+) neuronal subpopulations play a role in adult neurogenesis and in AD pathology, particularly at early disease stages, suggesting that these neurons may serve as potential predictors of future AD in non-demented individuals.

Una revisión de los avances en la terapéutica de la enfermedad de Alzheimer: estrategia frente a la proteína β-amiloide

INTRODUCTION Alzheimer disease (AD) is a major neurodegenerative disorder which eventually results in total intellectual disability. The high global prevalence and the socioeconomic burden associated with the disease pose major challenges for public health in the 21st century. In this review we focus on both existing treatments and the therapies being developed, which principally target the β-amyloid protein. DISCUSSION The amyloidogenic hypothesis proposes that β-amyloid plays a key role in AD. Several pharmacological approaches aim to reduce the formation of β-amyloid peptides by inhibiting the β-secretase and γ-secretase enzymes. In addition, both passive and active immunotherapies have been developed for the purpose of inhibiting β-amyloid peptide aggregation. CONCLUSIONS Progress in identifying the molecular basis of AD may provide better models for understanding the causes of this neurodegenerative disease. The lack of efficacy of solanezumab (a humanised monoclonal antibody that promotes β-amyloid clearance in the brain), demonstrated by 2 recent Phase III clinical trials in patients with mild AD, suggests that the amyloidogenic hypothesis needs to be revised.