Expression of somatostatin receptor subtypes (SSTR1–5) in Alzheimer’s disease brain: An immunohistochemical analysis

Exploring the Therapeutic Potential of Gamma-Aminobutyric Acid in Stress and Depressive Disorders through the Gut-Brain Axis

Research conducted on individuals with depression reveals that major depressive disorders (MDDs) coincide with diminished levels of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) in the brain, as well as modifications in the subunit composition of the primary receptors (GABAA receptors) responsible for mediating GABAergic inhibition. Furthermore, there is substantial evidence supporting the significant role of GABA in regulating stress within the brain, which is a pivotal vulnerability factor in mood disorders. GABA is readily available and approved as a food supplement in many countries. Although there is substantial evidence indicating that orally ingested GABA may affect GABA receptors in peripheral tissues, there is comparatively less evidence supporting its direct action within the brain. Emerging evidence highlights that oral GABA intake may exert beneficial effects on the brain and psyche through the gut-brain axis. While GABA enjoys wide consumer acceptance in Eastern Asian markets, with many consumers reporting favorable effects on stress regulation, mood, and sleep, rigorous independent research is still largely lacking. Basic research, coupled with initial clinical findings, makes GABA an intriguing neuro-nutritional compound deserving of clinical studies in individuals with depression and other psychological problems.

Structural dynamics and catalytic modulations of Aβ regulating enzymes as future outlook for Alzheimer's

Aβ cascade hypothesis being considered most evident event in AD pathology and even today it holds good. Dysregulation of catalytic events of Aβ regulating enzymes can possibly cause faulty Aβ trafficking; inequity of Aβ formation and clearance resulting in misfolded protein accumulation, neurodegeneration and cognitive impairment. Many novel approaches have been made on this pathway to discover new molecules, unfortunately couldn't reach the terminal phases of clinical trials. Over decades, studies have been more focused on enzyme chemistry and explored the relationship between structural features and catalytic function of Aβ regulating enzymes. However, the modulations of catalytic mechanisms of those enzymes have not been imposed so far to reduce the Aβ load. Hence, in this review, we have critically detailed the knowledge of basic structural dynamics and possible catalytic modulations of enzymes responsible for Aβ formation and clearance that will impart new perspectives in drug discovery process.

Regulatory mechanisms of tetramethylpyrazine on central nervous system diseases: A review

Central nervous system (CNS) diseases can lead to motor, sensory, speech, cognitive dysfunction, and sometimes even death. These diseases are recognized to cause a substantial socio-economic impact on a global scale. Tetramethylpyrazine (TMP) is one of the main active ingredients extracted from the Chinese herbal medicine Ligusticum striatum DC. (Chuan Xiong). Many in vivo and in vitro studies have demonstrated that TMP has a certain role in the treatment of CNS diseases through inhibiting calcium ion overload and glutamate excitotoxicity, anti-oxidative/nitrification stress, mitigating inflammatory response, anti-apoptosis, protecting the integrity of the blood-brain barrier (BBB) and facilitating synaptic plasticity. In this review, we summarize the roles and mechanisms of action of TMP on ischemic cerebrovascular disease, spinal cord injury, Parkinson’s disease, Alzheimer’s disease, cognitive impairments, migraine, and depression. Our review will provide new insights into the clinical applications of TMP and the development of novel therapeutics.

Neuropeptide System Regulation of Prefrontal Cortex Circuitry: Implications for Neuropsychiatric Disorders

Neuropeptides, a diverse class of signaling molecules in the nervous system, modulate various biological effects including membrane excitability, synaptic transmission and synaptogenesis, gene expression, and glial cell architecture and function. To date, most of what is known about neuropeptide action is limited to subcortical brain structures and tissue outside of the central nervous system. Thus, there is a knowledge gap in our understanding of neuropeptide function within cortical circuits. In this review, we provide a comprehensive overview of various families of neuropeptides and their cognate receptors that are expressed in the prefrontal cortex (PFC). Specifically, we highlight dynorphin, enkephalin, corticotropin-releasing factor, cholecystokinin, somatostatin, neuropeptide Y, and vasoactive intestinal peptide. Further, we review the implication of neuropeptide signaling in prefrontal cortical circuit function and use as potential therapeutic targets. Together, this review summarizes established knowledge and highlights unknowns of neuropeptide modulation of neural function underlying various biological effects while offering insights for future research. An increased emphasis in this area of study is necessary to elucidate basic principles of the diverse signaling molecules used in cortical circuits beyond fast excitatory and inhibitory transmitters as well as consider components of neuropeptide action in the PFC as a potential therapeutic target for neurological disorders. Therefore, this review not only sheds light on the importance of cortical neuropeptide studies, but also provides a comprehensive overview of neuropeptide action in the PFC to serve as a roadmap for future studies in this field.

Molecular Signature of Astrocytes for Gene Delivery by the Synthetic Adeno-Associated Viral Vector rAAV9P1

Astrocytes have crucial functions in the central nervous system (CNS) and are major players in many CNS diseases. Research on astrocyte-centered diseases requires efficient and well-characterized gene transfer vectors. Vectors derived from the Adeno-associated virus serotype 9 (AAV9) target astrocytes in the brains of rodents and nonhuman primates. A recombinant (r) synthetic peptide-displaying AAV9 variant, rAAV9P1, that efficiently and selectively transduces cultured human astrocytes, has been described previously. Here, it is shown that rAAV9P1 retains astrocyte-targeting properties upon intravenous injection in mice. Detailed analysis of putative receptors on human astrocytes shows that rAAV9P1 utilizes integrin subunits αv, β8, and either β3 or β5 as well as the AAV receptor AAVR. This receptor pattern is distinct from that of vectors derived from wildtype AAV2 or AAV9. Furthermore, a CRISPR/Cas9 genome-wide knockout screening revealed the involvement of several astrocyte-associated intracellular signaling pathways in the transduction of human astrocytes by rAAV9P1. This study delineates the unique receptor and intracellular pathway signatures utilized by rAAV9P1 for targeting human astrocytes. These results enhance the understanding of the transduction biology of synthetic rAAV vectors for astrocytes and can promote the development of advanced astrocyte-selective gene delivery vehicles for research and clinical applications.

A computational study of somatostatin subtype-4 receptor agonist binding

The somatostatin subtype-4 receptor (sst4) is highly expressed in neocortical and hippocampal areas, which are affected by amyloid beta accumulation. Sst4 agonists enhance downstream activity of amyloid beta peptide catabolism through neprilysin and may slow the progression of Alzheimer’s disease (AD). Sst4 is a G protein coupled receptor (GPCR), the structure of which has yet to be resolved. A newly constructed sst4 homology model, along with a previously reported model-built sst4 receptor structure, were used in the present study to gain insights into binding requirements of sst4 agonists employing a set of compounds patented by Boehringer Ingelheim. Besides aiming at delineating binding at the macromolecular level of these recently disclosed compounds, our objectives included the generation of a quantitative structure-activity relationship (QSAR) global model to explore the relationship between chemical structure and affinity. Through the implementation of model building, docking, and QSAR, plausible correlations between structural properties and the binding affinity are established. This study sheds light on understanding binding requirements at the sst4 receptor.

Graphical abstract

Sleep Disturbance and Alzheimer's Disease: The Glial Connection

Poor quality and quantity of sleep are very common in elderly people throughout the world. Growing evidence has suggested that sleep disturbances could accelerate the process of neurodegeneration. Recent reports have shown a positive correlation between sleep deprivation and amyloid-β (Aβ)/tau aggregation in the brain of Alzheimer's patients. Glial cells have long been implicated in the progression of Alzheimer's disease (AD) and recent findings have also suggested their role in regulating sleep homeostasis. However, how glial cells control the sleep-wake balance and exactly how disturbed sleep may act as a trigger for Alzheimer's or other neurological disorders have recently gotten attention. In an attempt to connect the dots, the present review has highlighted the role of glia-derived sleep regulatory molecules in AD pathogenesis. Role of glia in sleep disturbance and Alzheimer's progression.

Transcriptome and Translatome Regulation of Pathogenesis in Alzheimer's Disease Model Mice

BACKGROUND

Defining cellular mechanisms that drive Alzheimer's disease (AD) pathogenesis and progression will be aided by studies defining how gene expression patterns change during pre-symptomatic AD and ensuing periods of declining cognition. Previous studies have emphasized changes in transcriptome, but not translatome regulation, leaving the ultimate results of gene expression alterations relatively unexplored in the context of AD.

OBJECTIVE

To identify genes whose expression might be regulated at the transcriptome and translatome levels in AD, we analyzed gene expression in cerebral cortex of two AD model mouse strains, CVN (APPSwDI;NOS2 -/- ) and Tg2576 (APPSw), and their companion wild type (WT) strains at 6 months of age by tandem RNA-Seq and Ribo-Seq (ribosome profiling).

METHODS

Identical starting pools of bulk RNA were used for RNA-Seq and Ribo-Seq. Differential gene expression analysis was performed at the transcriptome, translatome, and translational efficiency levels. Regulated genes were functionally evaluated by gene ontology tools.

RESULTS

Compared to WT mice, AD model mice had similar levels of transcriptome regulation, but differences in translatome regulation. A microglial signature associated with early stages of Aβ accumulation was upregulated at both levels in CVN mice. Although the two mice strains did not share many regulated genes, they showed common regulated pathways related to AβPP metabolism associated with neurotoxicity and neuroprotection.

CONCLUSION

This work represents the first genome-wide study of brain translatome regulation in animal models of AD and provides evidence of a tight and early translatome regulation of gene expression controlling the balance between neuroprotective and neurodegenerative processes in brain.

NNC 26-9100 increases Aβ1-42 phagocytosis, inhibits nitric oxide production and decreases calcium in BV2 microglia cells

Microglia are the resident immune cell of the brain involved in the development and progression of Alzheimer's disease (AD). Modulation of microglia activity represents a potential mechanism for treating AD. Herein, the compound NNC 26-9100 (NNC) was evaluated in toxicity, nitric oxide release, Aβ1-42 uptake and cytosolic calcium assays during lipopolysaccharide (LPS)-activated conditions using mouse BV2 microglia cells. After 24 hours, LPS increased cell toxicity in the alamar blue and lactate dehydrogenase assays, increased nitrite release, and increase cytoplasmic calcium. Addition of NNC decreased the LPS-induce lactate dehydrogenase release, had no effect in the alamar blue assay, decreased nitrite release and decreased cytosolic calcium. In the absence of LPS, NNC increased uptake of FITC-tagged Aβ1-42. These data demonstrate that NNC treatment decreases nitrosative stress and microglia cell damage during LPS-induced activation and enhances phagocytosis of Aβ1-42 during non-inflammatory conditions. Thus, NNC 26-9100 may have beneficial effects in AD and in inflammatory diseases of the brain through enhancement of microglial Aβ clearance, and cell protective effects through prevention of elevated cytosolic calcium and inhibition of nitric oxide release.

Inactivation of Presenilin in inhibitory neurons results in decreased GABAergic responses and enhanced synaptic plasticity

Mutations in the Presenilin genes are the major genetic cause of Alzheimer's disease (AD). Presenilin (PS) is highly expressed in the hippocampus, which is particularly vulnerable in AD. Previous studies of PS function in the hippocampus, however, focused exclusively on excitatory neurons. Whether PS regulates inhibitory neuronal function remained unknown. In the current study, we investigate PS function in GABAergic neurons by performing whole-cell and field-potential electrophysiological recordings using acute hippocampal slices from inhibitory neuron-specific PS conditional double knockout (IN-PS cDKO) mice at 2 months of age, before the onset of age-dependent loss of interneurons. We found that the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) is reduced in hippocampal CA1 neurons of IN-PS cDKO mice, whereas the amplitude of sIPSCs is normal. Moreover, the efficacy of inhibitory neurotransmission as assessed with synaptic input/output relations for evoked mono- and di-synaptic IPSCs is markedly lowered in hippocampal CA1 neurons of IN-PS cDKO mice. Consistent with these findings, IN-PS cDKO mice display enhanced paired-pulse facilitation, frequency facilitation and long-term potentiation in the Schaffer collateral-CA1 pathway. Interestingly, depletion of intracellular Ca2+ stores by inhibition of sarcoendoplasmic reticulum Ca2+ ATPase results in a reduction of IPSC amplitude in control hippocampal neurons but not in IN-PS cDKO neurons, suggesting that impaired intracellular calcium homeostasis in the absence of PS may contribute to the deficiencies in inhibitory neurotransmission. Furthermore, the amplitude of IPSCs induced by short trains of presynaptic stimulation and paired-pulse ratio are decreased in IN-PS cDKO mice. These findings show that inactivation of PS in interneurons results in decreased GABAergic responses and enhanced synaptic plasticity in the hippocampus, providing additional evidence for the importance of PS in the regulation of synaptic plasticity and calcium homeostasis.

The role of neuropeptide somatostatin in the brain and its application in treating neurological disorders

Somatostatin (SST) is a well-known neuropeptide that is expressed throughout the brain. In the cortex, SST is expressed in a subset of GABAergic neurons and is known as a protein marker of inhibitory interneurons. Recent studies have identified the key functions of SST in modulating cortical circuits in the brain and cognitive function. Furthermore, reduced expression of SST is a hallmark of various neurological disorders, including Alzheimer's disease and depression. In this review, we summarize the current knowledge on SST expression and function in the brain. In particular, we describe the physiological roles of SST-positive interneurons in the cortex. We further describe the causal relationship between pathophysiological changes in SST function and various neurological disorders, such as Alzheimer's disease. Finally, we discuss potential treatments and possibility of novel drug developments for neurological disorders based on the current knowledge on the function of SST and SST analogs in the brain derived from experimental and clinical studies.

Prepubertal exposure to high dose of cadmium induces hypothalamic injury through transcriptome profiling alteration and neuronal degeneration in female rats

Cadmium (Cd) is a toxic metal, which seems to be crucial during the prepubertal period. Cd can destroy the structural integrity of the blood-brain barrier (BBB) and enters into the brain. Although the brain is susceptible to neurotoxicity induced by Cd, the effects of Cd on the brain, particularly hypothalamic transcriptome, are still relatively poorly understood. Therefore, we investigated the molecular effects of Cd exposure on the hypothalamus by profiling the transcriptomic response of the hypothalamus to high dose of Cd (25 mg/kg bw/day cadmium chloride (CdCl₂)) during the prepubertal period in Sprague-Dawley female rats. After sequencing and annotation, differential expression analysis revealed 1656 genes that were differentially expressed that 108 of them were classified into 37 transcription factor (TF) families. According to gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, these differentially expressed genes (DEGs) were involved in different biological processes and neurological disorders including Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD), prolactin signaling pathway, PI3K/Akt signaling, and dopaminergic synapse. Five transcripts were selected for further analyses with Real-time quantitative PCR (RT-qPCR). The RT-qPCR results were mostly consistent with those from the high throughput RNA sequencing (RNA-seq). Cresyl violet staining clearly showed an increased neuronal degeneration in the dorsomedial hypothalamus (DMH) and arcuate (Arc) nuclei of the CdCl₂ group. Overall, this study demonstrates that prepubertal exposure to high doses of Cd induces hypothalamic injury through transcriptome profiling alteration in female rats, which reveals the new mechanisms of pathogenesis of Cd in the hypothalamus.

Somatostatin Ameliorates β-Amyloid-Induced Cytotoxicity via the Regulation of CRMP2 Phosphorylation and Calcium Homeostasis in SH-SY5Y Cells

Somatostatin is involved in the regulation of multiple signaling pathways and affords neuroprotection in response to neurotoxins. In the present study, we investigated the role of Somatostatin-14 (SST) in cell viability and the regulation of phosphorylation of Collapsin Response Mediator Protein 2 (CRMP2) (Ser522) via the blockade of Ca²⁺ accumulation, along with the inhibition of cyclin-dependent kinase 5 (CDK5) and Calpain activation in differentiated SH-SY5Y cells. Cell Viability and Caspase 3/7 assays suggest that the presence of SST ameliorates mitochondrial stability and cell survival pathways while augmenting pro-apoptotic pathways activated by Aβ. SST inhibits the phosphorylation of CRMP2 at Ser522 site, which is primarily activated by CDK5. Furthermore, SST effectively regulates Ca²⁺ influx in the presence of Aβ, directly affecting the activity of calpain in differentiated SH-SY5Y cells. We also demonstrated that SSTR2 mediates the protective effects of SST. In conclusion, our results highlight the regulatory role of SST in intracellular Ca²⁺ homeostasis. The neuroprotective role of SST via axonal regeneration and synaptic integrity is corroborated by regulating changes in CRMP2; however, SST-mediated changes in the blockade of Ca²⁺ influx, calpain expression, and toxicity did not correlate with CDK5 expression and p35/25 accumulation. To summarize, our findings suggest two independent mechanisms by which SST mediates neuroprotection and confirms the therapeutic implications of SST in AD as well as in other neurodegenerative diseases where the effective regulation of calcium homeostasis is required for a better prognosis.

Enhanced neprilysin-mediated degradation of hippocampal Aβ42 with a somatostatin peptide that enters the brain

Background: Aggregation of the amyloid-beta (Aβ) peptide is one of the main neuropathological events in Alzheimer's disease (AD). Neprilysin is the major enzyme degrading Aβ, with its activity enhanced by the neuropeptide somatostatin (SST). SST levels are decreased in the brains of AD patients. The poor delivery of SST over the blood-brain barrier (BBB) and its extremely short half-life of only 3 min limit its therapeutic significance.

Methods: We recombinantly fused SST to a BBB transporter binding to the transferrin receptor. Using primary neuronal cultures and neuroblastoma cell lines, the ability of the formed fusion protein to activate neprilysin was studied. SST-scFv8D3 was administered to mice overexpressing the Aβ-precursor protein (AβPP) with the Swedish mutation (APPswe) as a single injection or as a course of three injections over a 72 h period. Levels of neprilysin and Aβ were quantified using an Enzyme-linked immunosorbent assay (ELISA). Distribution of SST-scFv8D3 in the brain, blood and peripheral organs was studied by radiolabeling with iodine-125.

Results: The construct, SST-scFv8D3, exhibited 120 times longer half-life than SST alone, reached the brain in high amounts when injected intravenously and significantly increased the brain concentration of neprilysin in APPswe mice. A significant decrease in the levels of membrane-bound Aβ42 was detected in the hippocampus and the adjacent cortical area after only three injections.

Conclusion: With intravenous injections of our BBB permeable SST peptide, we were able to significantly increase the levels neprilysin, an effect that was followed by a significant and selective degradation of membrane-bound Aβ42 in the hippocampus. Being that membrane-bound Aβ triggers neuronal toxicity and the hippocampus is the central brain area in the progression of AD, the study has illuminated a new potential treatment paradigm with a promising safety profile targeting only the disease affected areas.

Aging-related modifications to G protein-coupled receptor signaling diversity

Aging is a highly complex molecular process, affecting nearly all tissue systems in humans and is the highest risk factor in developing neurodegenerative disorders such as Alzheimer's and Parkinson's disease, cardiovascular disease and Type 2 diabetes mellitus. The intense complexity of the aging process creates an incentive to develop more specific drugs that attenuate or even reverse some of the features of premature aging. As our current pharmacopeia is dominated by therapeutics that target members of the G protein-coupled receptor (GPCR) superfamily it may be prudent to search for effective anti-aging therapeutics in this fertile domain. Since the first demonstration of GPCR-based β-arrestin signaling, it has become clear that an enhanced appreciation of GPCR signaling diversity may facilitate the creation of therapeutics with selective signaling activities. Such 'biased' ligand signaling profiles can be effectively investigated using both standard molecular biological techniques as well as high-dimensionality data analyses. Through a more nuanced appreciation of the quantitative nature across the multiple dimensions of signaling bias that drugs possess, researchers may be able to further refine the efficacy of GPCR modulators to impact the complex aberrations that constitute the aging process. Identifying novel effector profiles could expand the effective pharmacopeia and assist in the design of precision medicines. This review discusses potential non-G protein effectors, and specifically their potential therapeutic suitability in aging and age-related disorders.

Cell-autonomous role of Presenilin in age-dependent survival of cortical interneurons

BACKGROUND

Mutations in the PSEN1 and PSEN2 genes are the major cause of familial Alzheimer's disease. Previous studies demonstrated that Presenilin (PS), the catalytic subunit of γ-secretase, is required for survival of excitatory neurons in the cerebral cortex during aging. However, the role of PS in inhibitory interneurons had not been explored.

METHODS

To determine PS function in GABAergic neurons, we generated inhibitory neuron-specific PS conditional double knockout (IN-PS cDKO) mice, in which PS is selectively inactivated by Cre recombinase expressed under the control of the endogenous GAD2 promoter. We then performed behavioral, biochemical, and histological analyses to evaluate the consequences of selective PS inactivation in inhibitory neurons.

RESULTS

IN-PS cDKO mice exhibit earlier mortality and lower body weight despite normal food intake and basal activity. Western analysis of protein lysates from various brain sub-regions of IN-PS cDKO mice showed significant reduction of PS1 levels and dramatic accumulation of γ-secretase substrates. Interestingly, IN-PS cDKO mice develop age-dependent loss of GABAergic neurons, as shown by normal number of GAD67-immunoreactive interneurons in the cerebral cortex at 2-3 months of age but reduced number of cortical interneurons at 9 months. Moreover, age-dependent reduction of Parvalbumin- and Somatostatin-immunoreactive interneurons is more pronounced in the neocortex and hippocampus of IN-PS cDKO mice. Consistent with these findings, the number of apoptotic cells is elevated in the cerebral cortex of IN-PS cDKO mice, and the enhanced apoptosis is due to dramatic increases of apoptotic interneurons, whereas the number of apoptotic excitatory neurons is unaffected. Furthermore, progressive loss of interneurons in the cerebral cortex of IN-PS cDKO mice is accompanied with astrogliosis and microgliosis.

CONCLUSION

Our results together support a cell-autonomous role of PS in the survival of cortical interneurons during aging. Together with earlier studies, these findings demonstrate a universal, essential requirement of PS in the survival of both excitatory and inhibitory neurons during aging.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

Enhancing microtubule stabilization rescues cognitive deficits and ameliorates pathological phenotype in an amyloidogenic Alzheimer's disease model

In Alzheimer's disease (AD), and other tauopathies, microtubule destabilization compromises axonal and synaptic integrity contributing to neurodegeneration. These diseases are characterized by the intracellular accumulation of hyperphosphorylated tau leading to neurofibrillary pathology. AD brains also accumulate amyloid-beta (Aβ) deposits. However, the effect of microtubule stabilizing agents on Aβ pathology has not been assessed so far. Here we have evaluated the impact of the brain-penetrant microtubule-stabilizing agent Epothilone D (EpoD) in an amyloidogenic model of AD. Three-month-old APP/PS1 mice, before the pathology onset, were weekly injected with EpoD for 3 months. Treated mice showed significant decrease in the phospho-tau levels and, more interesting, in the intracellular and extracellular hippocampal Aβ accumulation, including the soluble oligomeric forms. Moreover, a significant cognitive improvement and amelioration of the synaptic and neuritic pathology was found. Remarkably, EpoD exerted a neuroprotective effect on SOM-interneurons, a highly AD-vulnerable GABAergic subpopulation. Therefore, our results suggested that EpoD improved microtubule dynamics and axonal transport in an AD-like context, reducing tau and Aβ levels and promoting neuronal and cognitive protection. These results underline the existence of a crosstalk between cytoskeleton pathology and the two major AD protein lesions. Therefore, microtubule stabilizers could be considered therapeutic agents to slow the progression of both tau and Aβ pathology.

HOTAIR Accelerates Dyskinesia in a MPTP-Lesioned Mouse Model of PD via SSTR1 Methylation-Mediated ERK1/2 Axis

Homeobox transcript antisense RNA (HOTAIR), has been associated with neuroprotective effects in Parkinson's disease (PD). However, the underlying mechanisms still remain unclear. Hence, this present study attempted to clarify the functional relevance of HOTAIR in PD. We established an in vivo mouse model of PD using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and an in vitro cell model of PD by treating dopaminergic neuron MN9D cells with 1-methyl-4-phenylpyridinium species (MPP+). The expressions of somatostatin receptor 1 (SSTR1) and HOTAIR were altered to examine their effects on MN9D cell viability and apoptosis, as well as on movement impairments in MPTP-induced PD mouse model. The results indicated that HOTAIR expression was upregulated and SSTR1 was downregulated in in vivo and in vitro PD models. HOTAIR could bind to the promoter region of SSTR1, resulting in an increase of SSTR1 methylation through the recruitment of DNA methyltransferases in PD cell models. Notably, overexpression of HOTAIR and silencing of SSTR1 enhanced dopaminergic neuron apoptosis in MN9D cells and exacerbated dyskinesia in MPTP-induced PD mouse model. Collectively, overexpressed HOTAIR stimulates DNA methylation of SSTR1 to reduce SSTR1 expression, thereby accelerating dyskinesia and facilitating dopaminergic neuron apoptosis in a MPTP-lesioned PD mouse model via activation of the ERK1/2 axis.

Somatostatin receptors (SSTR1-5) on inhibitory interneurons in the barrel cortex

Inhibitory interneurons in the cerebral cortex contain specific proteins or peptides characteristic for a certain interneuron subtype. In mice, three biochemical markers constitute non-overlapping interneuron populations, which account for 80–90% of all inhibitory cells. These interneurons express parvalbumin (PV), somatostatin (SST), or vasoactive intestinal peptide (VIP). SST is not only a marker of a specific interneuron subtype, but also an important neuropeptide that participates in numerous biochemical and signalling pathways in the brain via somatostatin receptors (SSTR1-5). In the nervous system, SST acts as a neuromodulator and neurotransmitter affecting, among others, memory, learning, and mood. In the sensory cortex, the co-localisation of GABA and SST is found in approximately 30% of interneurons. Considering the importance of interactions between inhibitory interneurons in cortical plasticity and the possible GABA and SST co-release, it seems important to investigate the localisation of different SSTRs on cortical interneurons. Here, we examined the distribution of SSTR1-5 on barrel cortex interneurons containing PV, SST, or VIP. Immunofluorescent staining using specific antibodies was performed on brain sections from transgenic mice that expressed red fluorescence in one specific interneuron subtype (PV-Ai14, SST-Ai14, and VIP-Ai14 mice). SSTRs expression on PV, SST, and VIP interneurons varied among the cortical layers and we found two patterns of SSTRs distribution in L4 of barrel cortex. We also demonstrated that, in contrast to other interneurons, PV cells did not express SSTR2, but expressed other SSTRs. SST interneurons, which were not found to make chemical synapses among themselves, expressed all five SSTR subtypes.

Distinct disease-sensitive GABAergic neurons in the perirhinal cortex of Alzheimer's mice and patients

Neuronal loss is the best neuropathological substrate that correlates with cortical atrophy and dementia in Alzheimer's disease (AD). Defective GABAergic neuronal functions may lead to cortical network hyperactivity and aberrant neuronal oscillations and in consequence, generate a detrimental alteration in memory processes. In this study, using immunohistochemical and stereological approaches, we report that the two major and non-overlapping groups of inhibitory interneurons (SOM-cells and PV-cells) displayed distinct vulnerability in the perirhinal cortex of APP/PS1 mice and AD patients. SOM-positive neurons were notably sensitive and exhibited a dramatic decrease in the perirhinal cortex of 6-month-old transgenic mice (57% and 61% in areas 36 and 35, respectively) and, most importantly, in AD patients (91% in Braak V-VI cases). In addition, this interneuron degenerative process seems to occur in parallel, and closely related, with the progression of the amyloid pathology. However, the population expressing PV was unaffected in APP/PS1 mice while in AD brains suffered a pronounced and significant loss (69%). As a key component of cortico-hippocampal networks, the perirhinal cortex plays an important role in memory processes, especially in familiarity-based memory recognition. Therefore, disrupted functional connectivity of this cortical region, as a result of the early SOM and PV neurodegeneration, might contribute to the altered brain rhythms and cognitive failures observed in the initial clinical phase of AD patients. Finally, these findings highlight the failure of amyloidogenic AD models to fully recapitulate the selective neuronal degeneration occurring in humans.

Gi/o-Protein Coupled Receptors in the Aging Brain

Cells translate extracellular signals to regulate processes such as differentiation, metabolism and proliferation, via transmembranar receptors. G protein-coupled receptors (GPCRs) belong to the largest family of transmembrane receptors, with over 800 members in the human species. Given the variety of key physiological functions regulated by GPCRs, these are main targets of existing drugs. During normal aging, alterations in the expression and activity of GPCRs have been observed. The central nervous system (CNS) is particularly affected by these alterations, which results in decreased brain functions, impaired neuroregeneration, and increased vulnerability to neuropathologies, such as Alzheimer's and Parkinson diseases. GPCRs signal via heterotrimeric G proteins, such as G_o, the most abundant heterotrimeric G protein in CNS. We here review age-induced effects of GPCR signaling via the G_i/o subfamily at the CNS. During the aging process, a reduction in protein density is observed for almost half of the G_i/o-coupled GPCRs, particularly in age-vulnerable regions such as the frontal cortex, hippocampus, substantia nigra and striatum. G_i/o levels also tend to decrease with aging, particularly in regions such as the frontal cortex. Alterations in the expression and activity of GPCRs and coupled G proteins result from altered proteostasis, peroxidation of membranar lipids and age-associated neuronal degeneration and death, and have impact on aging hallmarks and age-related neuropathologies. Further, due to oligomerization of GPCRs at the membrane and their cooperative signaling, down-regulation of a specific G_i/o-coupled GPCR may affect signaling and drug targeting of other types/subtypes of GPCRs with which it dimerizes. G_i/o-coupled GPCRs receptorsomes are thus the focus of more effective therapeutic drugs aiming to prevent or revert the decline in brain functions and increased risk of neuropathologies at advanced ages.

Capacitive Micromachined Ultrasonic Transducer (CMUT)-based Biosensor for Detection of Low Concentration Neuropeptide

Accurate detection of neuropeptides in cerebrospinal fluid (CSF) plays an important role in both indepth studies and early diagnosis of neurological diseases. Here, we report a biosensor based on Capacitive Micromachined Ultrasonic Transducer (CMUT) which is capable of detecting low concentrations (pg $\sim $ ng/ml) of a neuropeptide involved with the progression of Alzheimer's diseases, somatostatin (SST). A 10-MHz CMUT was fabricated and utilized as a physical resonant sensor which detects the change in the concentration of analyte through the mass-loading mechanism. The resonant plate was sequentially coated with protein G and antibodies to provide specificity to SST; Cysteine-tagged protein G layer enables controlled immobilization of antibodies in a welloriented manner. The change in the resonant frequency of the CMUT sensor was measured after incubating the sensor in various concentrations of SST. The significant shifts in the resonant frequency were observed for SST concentrations in the range of 10 pg/ml $\sim 1$ ng/ml. Compared to the previously reported biosensors developed for SST detection, our sensor shows discernable responses for SST that are $\sim 6$ orders of magnitude lower in concentration. Thus, this work demonstrates the potential of the CMUT resonant sensor as a promising biosensor platform for detection of neuropeptides involved with neurodegenerative diseases that often exist in low concentrations in CSF.

Centrally Administered Cortistation-14 Induces Antidepressant-Like Effects in Mice via Mediating Ghrelin and GABAA Receptor Signaling Pathway

Cortistatin-14 (CST-14), a recently discovered cyclic neuropeptide, can bind to all five cloned somatostatin receptors (SSTRs) and ghrelin receptor to exert its biological activities and co-exists with GABA within the cortex and hippocampus. However, the role of CST-14 in the control of depression processes is not still clarified. Here, we tested the behavioral effects of CST-14 in the in a variety of classical rodent models of depression [forced swimming test (FST), tail suspension test (TST) and novelty-suppressed feeding test]. In the models of depression, CST-14 produced antidepressant-like effects, and does not altered locomotor activity levels. And, we found that CST-14 mRNA and BDNF mRNA were significantly decreased in the hippocampus and cortex after mice exposed to stress. Further data show that i.c.v. administration of CST-14 produce rapid antidepressant effects, and does not altered locomotor activity levels. Then these antidepressant-like effects were significantly reversed by [D-Lys₃]GHRP-6 (ghrelin receptor antagonist), but not c-SOM (SSTRs antagonist). Meanwhile, the effects of some neurotransmitter blockers indicates that only GABA_A system, but not CRF1 receptor, α/β-adrenergic receptor, is involved in the antidepressant effect of CST-14. The effects of the mTOR inhibitor (rapamycin), the PI3K inhibitor (LY294002) and the p-ERK1/2 inhibitor (U0126) suggesting that the ERK/mTOR or PI3K/Akt/mTOR signaling pathway is not involved in the antidepressant effects of CST-14. Interestingly, intranasal administration of CST-14 led to reducing depressive-like behavior, and near-infrared fluorescent experiments showed the real-time in vivo bio-distribution in brain after intranasal infusion of Cy7.5-CST-14. Taken all together, the results of present study point to a role for CST-14 in the modulation of depression processes via the ghrelin and GABA_A receptor, and suggest cortistation may represent a novel strategy for the treatment of depression disorders.

Highlights:-

CST-14 and BDNF mRNA are decreased in hippocampus and cortex once mice exposed to stress.

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i.c.v. or intranasal administration of CST-14 produce rapid antidepressant effects.

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NIR fluorescence imaging detected the brain uptake and distribution after intranasal CST-14.

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Antidepressant effects of CST-14 were only related to ghrelin and GABA_A system.

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Co-injection of CST-14 and NPS produce antidepressant effect, and do not impair memory.

Somatostatin Maintains Permeability and Integrity of Blood-Brain Barrier in β-Amyloid Induced Toxicity

In Alzheimer's disease (AD), the impaired clearance of β-amyloid peptide (Aβ) due to disrupted tight junction and transporter proteins is the prominent cause of disease progression. Somatostatin (SST) blocks the aggregation of Aβ and inflammation whereas reduction of SST levels in the CSF and brain tissue is associated with impaired cognitive function and memory loss. However, the role of SST in preservation of blood-brain barrier (BBB) integrity and functionality in Aβ-induced toxicity is not known. In the present study using human CMEC/D3 cells, we demonstrate that SST prevents Aβ-induced BBB permeability by regulating LRP1 and RAGE expression and improving the disrupted tight junction proteins. Furthermore, SST abrogates Aβ-induced JNK phosphorylation and expression of MMP2. Taken together, results presented here suggest that SST might serve as a therapeutic intervention in AD via targeting multiple pathways responsible for neurotoxicity, impaired BBB function, and disease progression.

Synaptic plasticity modulation by circulating peptides and metaplasticity: Involvement in Alzheimer's disease

Synaptic plasticity is a cellular process involved in learning and memory whose alteration in its two main forms (Long Term Depression (LTD) and Long Term Potentiation (LTP)), is observed in most brain pathologies, including neurodegenerative disorders such as Alzheimer's disease (AD). In humans, AD is associated at the cellular level with neuropathological lesions composed of extracellular deposits of β-amyloid (Aβ) protein aggregates and intracellular neurofibrillary tangles, cellular loss, neuroinflammation and a general brain homeostasis dysregulation. Thus, a dramatic synaptic environment perturbation is observed in AD patients, involving changes in brain neuropeptides, cytokines, growth factors or chemokines concentration and diffusion. Studies performed in animal models demonstrate that these circulating peptides strongly affect synaptic functions and in particular synaptic plasticity. Besides this neuromodulatory action of circulating peptides, other synaptic plasticity regulation mechanisms such as metaplasticity are altered in AD animal models. Here, we will review new insights into the study of synaptic plasticity regulatory/modulatory mechanisms which could influence the process of synaptic plasticity in the context of AD with a particular attention to the role of metaplasticity and peptide dependent neuromodulation.

Clinical and functional implication of the components of somatostatin system in gastroenteropancreatic neuroendocrine tumors

PURPOSE

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) comprise a heterogeneous group of malignancies often presenting with metastasis at diagnosis and whose clinical outcome is difficult to predict. Somatostatin (SST) analogs (SSAs) provide a valuable pharmacological tool to palliate hormonal symptoms, and control progression in some NETs. However, many patients do not respond to SSAs or develop resistance, and there are many uncertainties regarding pathophysiology of SST and its receptors (sst1-sst5) in GEP-NETs.

METHODS

The expression of SST system components in GEP-NETs was determined, compared with that of non-tumor adjacent and normal tissues and correlated with clinical and histological characteristics. Specifically, 58 patients with GEP-NETs and 14 normal samples were included. Cell viability in NET cell lines was determined in response to specific SSAs.

RESULTS

Normal samples and non-tumor adjacent tissues presented a similar expression profile, with appreciable expression of sst2 and sst3, and a lower expression of the other receptors. In contrast, cortistatin, sst1, sst4, and sst5 were overexpressed in tumors, while sst3 and sst4 seemed overexpressed in less differentiated tumors. Some SST system components were related to vascular/nerve invasion and metastasis. In vitro, sst1 and sst3 agonists reduced viability in BON-1 cells, while they, similar to octreotide and pasireotide, increased viability in QGP-1 cells.

CONCLUSIONS

These results provide novel information on SST system pathophysiology in GEP-NETs, including relevant associations with clinical-histological parameters, which might help to better understand the intrinsic heterogeneity of NETs and to identify novel biomarkers and/or targets with potential prognostic and/or therapeutic value for GEP-NETs patients.

Regional and subcellular distribution of GABAC ρ3 receptor in brain of R6/2 mouse model of Huntington's disease

In the present study, we describe the distribution of GABA_C ρ3 receptor immunoreactivity in the cortex, striatum and hippocampus of wild type (wt) and 11 weeks old HD transgenic (tg) R6/2 mouse brain. In the brain of wt mice, GABA_C ρ3 immunoreactivity is well expressed in neuronal cells, nerve fibers and axonal processes. In comparison to wt, GABA_C ρ3 receptor like immunoreactivity decreases significantly in all three brain regions of R6/2 mice. The altered distributional pattern and significant changes in GABA_C ρ3 receptor immunoreactivity as seen in the R6/2 mouse brain might be a plausible molecular mechanism for excitotoxicity in HD pathogenesis due to the loss of inhibitory input.

Somatostatin receptor 5 is a prominent regulator of signaling pathways in cells with coexpression of Cannabinoid receptors 1

Endocannabinoids and somatostatin (SST) play critical roles in several pathophysiological conditions via binding to different receptor subtypes. Cannabinoid receptor 1 (CB1R) and somatostatin receptors (SSTRs) are expressed in several brain regions and share overlapping functions. Whether these two prominent members of G-protein-coupled receptor (GPCR) family interact with each other and constitute a functional receptor complex is not known. In the present study, we investigated the colocalization of CB1R and SSTR5 in rat brain, and studied receptor internalization, interaction and signal transduction pathways in HEK-293 cells cotransfected with human cannabinoid receptor 1 (hCB1R) and hSSTR5. Our results showed that CB1R and SSTR5 colocalized in rat brain cortex, striatum, and hippocampus. CB1R was expressed in SSTR5 immunoprecipitate prepared from the brain tissue lysate, indicating their association in a system where these receptors are endogenously expressed. In cotransfected HEK-293 cells, SSTR5 and CB1R existed in a constitutive heteromeric complex under basal condition, which was disrupted upon agonist treatments. Furthermore, concurrent receptor activation led to preferential formation of SSTR5 homodimer and dissociation of CB1R homodimer. We also discovered that second messenger cyclic adenosine monophosphate and downstream signaling pathways were modulated in a SSTR5-dominant and concentration-dependent manner in the presence of receptor-specific agonist. In conclusion, with predominant role of SSTR5, the functional consequences of crosstalk between SSTR5 and CB1R resulting in the regulation of receptor trafficking and signal transduction pathways open new therapeutic avenue in cancer biology and excitotoxicity.

Association of Pancreatic Polypeptide with Mild Cognitive Impairment Varies by APOE ε4 Allele

We conducted a preliminary case-control investigation of the association of pancreatic polypeptide (PP) with mild cognitive impairment (MCI) in 202 MCI cases (mean age, 81.6 years) and 202 age- and sex-matched cognitively normal controls in the Mayo Clinic Study of Aging. Plasma PP was measured and examined as the natural logarithm (continuous) and dichotomized at the median. The OR (95% CI) of MCI increased with increasing PP [1.46 (1.04-2.05)]. There was a negative interaction of PP with apolipoprotein E (APOE) ε4 allele; compared to the reference group (no APOE ε4 allele and low PP), the OR (95% CI) for combinations of ε4 and PP were: 2.64 (1.39-5.04) for APOE ε4 plus low PP; 2.09 (1.27-3.45) for no APOE ε4 plus high PP; and 1.91 (1.04-3.53) for no APOE ε4 plus high PP (P for interaction = 0.017). There was also a trend toward a negative interaction with type 2 diabetes (P for interaction = 0.058). Compared to no diabetes and low PP, the OR (95% CI) was 3.02 (1.22-7.46) for low PP plus diabetes but 1.80 (1.01-3.22) for high PP plus diabetes. Participants with high PP had a greater mean (SD) weight loss (kilograms per decade) than persons with low PP [-2.27 (4.07) vs. -1.61 (5.24); P = 0.016]. MCI cases had a non-significantly greater weight loss per decade compared to controls. These findings suggest that high PP alone or jointly with APOE ε4 allele or type 2 diabetes is associated with MCI, and that high PP may mitigate some effects of APOE ε4 allele and type 2 diabetes on cognition. Potential mechanisms may involve PP-related weight loss and centrally mediated effects of PP on cognition. These findings remain to be validated in other studies.

Pancreatic polypeptide inhibits somatostatin secretion

Pancreatic polypeptide (PP) is a major agonist for neuropeptide Y4 receptors (NPY4R). While NPY4R has been identified in various tissues, the cells on which it is expressed and its function in those cells has not been clearly delineated. Here we report that NPY4R is present in all somatostatin-containing cells of tissues that we tested, including pancreatic islets, duodenum, hippocampus, and hypothalamus. Its agonism by PP decreases somatostatin secretion from human islets. Mouse embryonic hippocampal (mHippo E18) cells expressed NPY4Rs and their activation by PP consistently decreased somatostatin secretion. Furthermore, central injection of PP in mice induced c-Fos immunoreactivity in somatostatin-containing cells in the hippocampus compared with PBS-injected mice. In sum, our results identify PP as a pivotal modulator of somatostatin secretion.

Hilar interneuron vulnerability distinguishes aged rats with memory impairment

Hippocampal interneuron populations are reportedly vulnerable to normal aging. The relationship between interneuron network integrity and age-related memory impairment, however, has not been tested directly. That question was addressed in the present study using a well-characterized model in which outbred, aged, male Long-Evans rats exhibit a spectrum of individual differences in hippocampal-dependent memory. Selected interneuron populations in the hippocampus were visualized for stereological quantification with a panel of immunocytochemical markers, including glutamic acid decarboxylase-67 (GAD67), somatostatin, and neuropeptide Y. The overall pattern of results was that, although the numbers of GAD67- and somatostatin-positive interneurons declined with age across multiple fields of the hippocampus, alterations specifically related to the cognitive outcome of aging were observed exclusively in the hilus of the dentate gyrus. Because the total number of NeuN-immunoreactive hilar neurons was unaffected, the decline observed with other markers likely reflects a loss of target protein rather than neuron death. In support of that interpretation, treatment with the atypical antiepileptic levetiracetam at a low dose shown previously to improve behavioral performance fully restored hilar SOM expression in aged, memory-impaired rats. Age-related decreases in GAD67- and somatostatin-immunoreactive neuron number beyond the hilus were regionally selective and spared the CA1 field of the hippocampus entirely. Together these findings confirm the vulnerability of hippocampal interneurons to normal aging and highlight that the integrity of a specific subpopulation in the hilus is coupled with age-related memory impairment.

Methylation analysis of SST and SSTR4 promoters in the neocortex of Alzheimer's disease patients

Several observations have pointed to a major pathogenic role of somatostatin depletion with respect to amyloid accumulation, which is often thought to be the crucial event in a cascade leading to Alzheimer's disease (AD). As methylation of CpG islands plays an important role in gene silencing, we studied the methylation status of the CpG islands in the promoters of somatostatin (SST) and in that of its receptor subtype in the cerebral cortex, SSTR4, in tissue samples from the middle temporal (Brodmann area 22) and superior frontal gyrus (Brodmann area 9) of 5 severely affected AD patients aged 72-94 years (Braak stages V-C or VI-C) and 5 non-demented controls aged 50-92 years. Bisulfite sequencing of DNA from cortical gray and infracortical white matter showed that the DNA methylation status at the promoters of SST and SSTR4 did not significantly differ between AD and control samples in any of the regions analyzed. We confirmed these results using deep bisulfite sequencing of PCR products from the SST promoter amplified from DNA from the cortical gray of the superior frontal gyrus of all AD patients and non-demented controls. We observed a trend toward increased DNA methylation with increasing age. In conclusion, deregulated somatostatin signaling in the AD cortices studied cannot be explained by hypermethylation of the SST or SSTR4 promoter CpG islands.

Inhibition of tumor promoting signals by activation of SSTR2 and opioid receptors in human breast cancer cells

Background

Somatostatin receptors (SSTRs) and opioid receptors (ORs) belong to the superfamily of G-protein coupled receptors and function as negative regulators of cell proliferation in breast cancer. In the present study, we determined the changes in SSTR subtype 2 (SSTR2) and μ, δ and κ-ORs expression, signaling cascades and apoptosis in three different breast cancer cells namely MCF-7, MDA-MB231 and T47D.

Methods

Immunocytochemistry and western blot analysis were employed to study the colocalization and changes in MAPKs (ERK1/2 and p38), cell survival pathway (PI3K/AKT) and tumor suppressor proteins (PTEN and p53) in breast cancer cell lines. The nature of cell death upon activation of SSTR2 or OR was analysed using flow cytometry analysis.

Results

The activation of SSTR2 and ORs modulate MAPKs (ERK1/2 and p38) in cell dependent and possibly estrogen receptor (ER) dependent manner. The activation of tumor suppressor proteins phosphatase and tensin homolog (PTEN) and p53 antagonized the PI3K/AKT cell survival pathway. Flow cytometry analyses reveal increased necrosis as opposed to apoptosis in MCF-7 and T47D cells when compared to ER negative MDA-MB231 cells. Furthermore, receptor and agonist dependent expression of ORs in SSTR2 immunoprecipitate suggest that SSTR2 and ORs might interact as heterodimers and inhibit epidermal growth factor receptor phosphorylation.

Conclusion

Taken together, findings indicate a new role for SSTR2/ORs in modulation of signaling pathways involved in cancer progression and provide novel therapeutic approaches in breast cancer treatment.

Somatostatin receptor subtype-4 agonist NNC 26-9100 mitigates the effect of soluble Aβ(42) oligomers via a metalloproteinase-dependent mechanism

Soluble amyloid-β peptide (Aβ) oligomers have been hypothesized to be primary mediators of Alzheimer's disease progression. In this regard, reduction of soluble Aβ-oligomers levels within the brain may provide a viable means in which to treat the disease. Somatostatin receptor subtype-4 (SSTR4) agonists have been proposed to reduce Aβ levels in the brain via enhancement of enzymatic degradation. Herein we evaluated the effect of selective SSTR4 agonist NNC 26-9100 on the changes in learning and soluble Aβ42 oligomer brain content with and without co-administration of the M13-metalloproteinase family enzyme-inhibitor phosphoramidon, using the senescence-accelerated mouse prone-8 (SAMP8) model. NNC 26-9100 treatment (0.2 µg i.c.v. in 2 µL) improved learning, which was blocked by phosphoramidon (1 and 10mM, respectively). NNC 26-9100 decreased total soluble Aβ42, an effect which was blocked by phosphoramidon (10mM). Extracellular, intracellular, and membrane fractions were then isolated from cortical tissue and assessed for soluble oligomer alterations. NNC 26-9100 decreased the Aβ42 trimeric (12 kDa) form within the extracellular and intracellular fractions, and produced a band-split effect of the Aβ42 hexameric (25 kDa) form within the extracellular fraction. These effects were also blocked by phosphoramdon (1 and 10mM, respectively). Subsequent evaluation of NNC 26-9100 in APPswe Tg2576 transgenic mice showed a similar learning improvement and corresponding reduction in soluble Aβ42 oligomers within extracellular, intracellular, and membrane fractions. These data support the hypothesis that NNC 26-9100 reduces soluble Aβ42 oligomers and enhances learning through a phosphoramidon-sensitive metalloproteinase-dependent mechanism.

Somatostatinergic systems: an update on brain functions in normal and pathological aging

Somatostatin is highly expressed in mammalian brain and is involved in many brain functions such as motor activity, sleep, sensory, and cognitive processes. Five somatostatin receptors have been described: sst(1), sst(2) (A and B), sst(3), sst(4), and sst(5), all belonging to the G-protein-coupled receptor family. During the recent years, numerous studies contributed to clarify the role of somatostatin systems, especially long-range somatostatinergic interneurons, in several functions they have been previously involved in. New advances have also been made on the alterations of somatostatinergic systems in several brain diseases and on the potential therapeutic target they represent in these pathologies.

Aβ-degrading enzymes: potential for treatment of Alzheimer disease

There is increasing evidence that deficient clearance of β-amyloid (Aβ) contributes to its accumulation in late-onset Alzheimer disease (AD). Several Aβ-degrading enzymes, including neprilysin (NEP), insulin-degrading enzyme, and endothelin-converting enzyme reduce Aβ levels and protect against cognitive impairment in mouse models of AD. The activity of several Aβ-degrading enzymes rises with age and increases still further in AD, perhaps as a physiological response to minimize the buildup of Aβ. The age- and disease-related changes in expression of more recently recognized Aβ-degrading enzymes (e.g. NEP-2 and cathepsin B) remain to be investigated, and there is strong evidence that reduced NEP activity contributes to the development of cerebral amyloid angiopathy. Regardless of the role of Aβ-degrading enzymes in the development of AD, experimental data indicate that increasing the activity of these enzymes (NEP in particular) has therapeutic potential in AD, although targeting their delivery to the brain remains a major challenge. The most promising current approaches include the peripheral administration of agents that enhance the activity of Aβ-degrading enzymes and the direct intracerebral delivery of NEP by convection-enhanced delivery. In the longer term, genetic approaches to increasing the intracerebral expression of NEP or other Aβ-degrading enzymes may offer advantages.

Somatostatin receptor 1 and 5 double knockout mice mimic neurochemical changes of Huntington's disease transgenic mice

BACKGROUND

Selective degeneration of medium spiny neurons and preservation of medium sized aspiny interneurons in striatum has been implicated in excitotoxicity and pathophysiology of Huntington's disease (HD). However, the molecular mechanism for the selective sparing of medium sized aspiny neurons and vulnerability of projection neurons is still elusive. The pathological characteristic of HD is an extensive reduction of the striatal mass, affecting caudate putamen. Somatostatin (SST) positive neurons are selectively spared in HD and Quinolinic acid/N-methyl-D-aspartic acid induced excitotoxicity, mimic the model of HD. SST plays neuroprotective role in excitotoxicity and the biological effects of SST are mediated by five somatostatin receptor subtypes (SSTR1-5).

METHODS AND FINDINGS

To delineate subtype selective biological responses we have here investigated changes in SSTR1 and 5 double knockout mice brain and compared with HD transgenic mouse model (R6/2). Our study revealed significant loss of dopamine and cAMP regulated phosphoprotein of 32 kDa (DARPP-32) and comparable changes in SST, N-methyl-D-aspartic acid receptors subtypes, calbindin and brain nitric oxide synthase expression as well as in key signaling proteins including calpain, phospho-extracellular-signal-regulated kinases1/2, synapsin-IIa, protein kinase C-α and calcineurin in SSTR1/5(-/-) and R6/2 mice. Conversely, the expression of somatostatin receptor subtypes, enkephalin and phosphatidylinositol 3-kinases were strain specific. SSTR1/5 appears to be important in regulating NMDARs, DARPP-32 and signaling molecules in similar fashion as seen in HD transgenic mice.

CONCLUSIONS

This is the first comprehensive description of disease related changes upon ablation of G- protein coupled receptor gene. Our results indicate that SST and SSTRs might play an important role in regulation of neurodegeneration and targeting this pathway can provide a novel insight in understanding the pathophysiology of Huntington's disease.

Immunohistochemical expression and localization of somatostatin receptor subtypes in androgen ablated prostate cancer

OBJECTIVE

The aim was to examine the expression and localization of the five somatostatin receptors (termed SSTR1 to 5) in radical prostatectomies (RPs) from patients with prostatic adenocarcinoma (PCa) under complete androgen ablation (CAA) before operation.

MATERIAL

The five SSTRs were evaluated in the epithelial, smooth muscle and endothelial cells of normal-looking epithelium (Nep), high-grade prostatic intraepithelial neoplasia (HGPIN) and PCa in 20 RPs with clinically detected PCa from patients under CAA. Twenty RPs with clinically detected PCa from hormonally untreated patients were used as control group.

RESULTS

Concerning the secretory cells (i) Membrane staining was seen for SSTR3 and SSTR4; the mean percentages of positive cells, higher in SSTR3 than in SSTR4, decreased sharply in HGPIN and PCa compared with Nep; the mean percentages in the androgen ablated group were 30% to 90% lower than in the untreated; (ii) Cytoplasmic staining was seen for all five SSTRs; the mean percentages of positive cells in Nep, HGPIN and PCa of the untreated group were similar, and in general as high as 80% or more; in the treated group, the Nep values were similar to those in the untreated, whereas the values in HGPIN and PCa were lower for SSTR1, three and five, with a decrease of 30% for SSTR1; (iii) Nuclear staining was seen with SSTR4 and SSTR5, the mean percentages for the former being much lower than for the latter; treatment affected both HGPIN and PCa, whose proportions of stained cells were 30% to 55% lower than in the untreated group. Cytoplasmic staining in the basal cells was seen for all five SSTRs, both in Nep and HGPIN. The values in the treated group were lower than in the other, the difference between the two group being in general comprised between 10% and 40%. Treatment did not affect SSTR staining in the smooth muscle and endothelial cells.

CONCLUSIONS

The present study expands our knowledge on the expression and localization of the five SSTRs in the prostate following CAA.

Lamina- and cell-specific alterations in cortical somatostatin receptor 2 mRNA expression in schizophrenia

Disturbed cortical γ-aminobutyric acid (GABA) neurotransmission in schizophrenia is evident from lamina- and cell type- specific alterations in presynaptic markers. In the dorsolateral prefrontal cortex (DLPFC), these alterations include lower transcript expression of glutamic acid decarboxylase (GAD67) and somatostatin (SST), a neuropeptide expressed in the Martinotti subpopulation of GABA neurons whose axons innervate the distal apical dendrites of pyramidal neurons. However, whether the alterations in SST-containing interneurons are associated with changes in post-synaptic receptors for SST has not been examined. Thus, we used in situ hybridization to quantify the mRNA expression levels of SST receptors subtype 1 (SSTR1) and subtype 2 (SSTR2) in DLPFC area 9 from 23 matched pairs of subjects with schizophrenia and normal comparison subjects. We also assessed the effects of potential confounding variables within the human subjects and in brain specimens from macaque monkeys with long term exposure to antipsychotic drugs. SSTR1 mRNA levels did not differ between subject groups. In contrast, mean cortical SSTR2 mRNA levels were significantly 19% lower in the subjects with schizophrenia. Laminar and cellular level analyses revealed that lower SSTR2 mRNA levels were localized to pyramidal cells in cortical layers 5-6. Expression of SSTR2 mRNA did not differ between monkeys exposed chronically to high doses of haloperidol or olanzapine and control animals, or between subjects with schizophrenia on or off antipsychotic medications at the time of death. However, levels of SSTR2 mRNA were significantly 37.6% lower in monkeys exposed chronically to low dose haloperidol, suggesting that the lower levels of SSTR2 mRNA selectively in pyramidal neurons in DLPFC layers 5-6 in schizophrenia should be interpreted with caution. In concert with prior findings of lower SST mRNA expression in the same subjects, the results of this study suggest the convergence of pre- and post-synaptic mechanisms to reduce inhibitory inputs to pyramidal neurons in the infragranular layers of the DLPFC.

Immunohistochemical expression and localization of somatostatin receptor subtypes in prostate cancer with neuroendocrine differentiation

The aim of the study is to examine the tissue expression and localization of the somatostatin receptors (SSTRs) in prostate cancer (PCa) with neuroendocrine (NE) differentiation. The five SSTR subtypes (SSTR1 to 5) were evaluated immunohistochemically in the secretory cells of normal-looking epithelium (Nep), high-grade prostatic intraepithelial neoplasia (HGPIN) and PCa in 20 radical prostatectomies (RPs) with Gleason score 3+3=6 acinar PCa; 20 RPs with GS 4+4=8 and 4+5=9 PCa; and 20 RPs with PCa with NE differentiation. The basal cells were evaluated in Nep and HGPIN. In all groups the stromal smooth muscle and endothelial cells were also analyzed. Concerning the secretory cells, (i) the greatest mean proportions of cells with strong cytoplasmic staining in PCa were seen for SSTR2, mainly in the group of RP with NE differentiation, and for SSTR4 in all three groups; the mean values in HGPIN were intermediate between Nep and PCa; (ii) Membrane staining was seen for SSTR3 and SSTR4; the mean percentages of positive cells, higher in SSTR3 than in SSTR4, decreased from Nep to HGPIN and PCa in all three RP groups; in the latter two, the mean percentages were similar; and (iii) Nuclear staining was seen with SSTR4 and SSTR5; for SSTR4, the mean percentages in the PCa of the three groups were higher than in HGPIN and Nep, the highest proportion being with PCa with NE differentiation. Concerning the basal cells, in Nep the mean proportions of cells with strong staining intensity were greater for SSTR1 and SSTR3 than for the other subtypes, the lowest being with SSTR2; in HGPIN the highest mean propositions of positive cells was with SSTR3, the proportions in the three RP groups being similar. Concerning the stromal smooth muscle and endothelial cells, the highest mean values being in SSTR1 and the lowest in SSTR5; for the former subtype the highest proportion of endothelial cells with strong intensity was seen in the RP NE group. In conclusion, this immunohistochemical study expands our knowledge on the expression and localization of five SSTRs in the various tissue components in the prostate with PCa with NE differentiation, compared with conventional PCa. Typing somatostatin receptor expression in NE tumours could be of relevance to target somatostatin analogue-based diagnostic approach and treatment.

Effects of insulin and octreotide on memory and growth hormone in Alzheimer's disease

Both insulin alone and the somatostatin analogue octreotide alone facilitate memory in patients with Alzheimer's disease (AD). Since octreotide inhibits endogenous insulin secretion, the cognitive effects of insulin and octreotide may not be independent. This study tested the individual and interactive effects of insulin and octreotide on memory and plasma growth hormone (GH) levels in older adults. Participants were 16 memory-impaired (AD = 7, amnestic mild cognitive impairment = 9; apolipoprotein E [APOE] epsilon4- [no epsilon4 alleles] = 9, epsilon4+ [1-2 epsilon4 alleles] = 7), and 19 cognitively-intact older adults (APOE epsilon4- = 17, epsilon4+ = 1). On separate days, fasting participants received counterbalanced infusions of: 1) insulin (1 mU.kg(-1).min(-1)) and dextrose to maintain euglycemia; 2) octreotide (150 microg/h); 3) insulin, dextrose, and octreotide; or 4) saline. Story recall was the principal endpoint. Insulin alone facilitated delayed recall for epsilon4- patients, relative to epsilon4+ patients (P = 0.0012). Furthermore, epsilon4- patients with higher Mattis Dementia Rating Scale (DRS) scores had greater octreotide-induced memory facilitation (P = 0.0298). For healthy adults, octreotide facilitated memory (P = 0.0122). Unexpectedly, hyperinsulinemia with euglycemia increased GH levels in healthy controls (P = 0.0299). Thus, insulin and octreotide appear to regulate memory in older adults. APOE epsilon4 genotype modulates responses to insulin and octreotide. Finally, insulin may regulate GH levels during euglycemia.