Anders Juréus

Galanin transgenic mice display cognitive and neurochemical deficits characteristic of Alzheimer's disease

Galanin is a neuropeptide with multiple inhibitory actions on neurotransmission and memory. In Alzheimers disease (AD), increased galanin-containing fibers hyperinnervate cholinergic neurons within the basal forebrain in association with a decline in cognition. We generated transgenic mice (GAL-tg) that overexpress galanin under the control of the dopamine β-hydroxylase promoter to study the neurochemical and behavioral sequelae of a mouse model of galanin overexpression in AD. Overexpression of galanin was associated with a reduction in the number of identifiable neurons producing acetylcholine in the horizontal limb of the diagonal band. Behavioral phenotyping indicated that GAL-tgs displayed normal general health and sensory and motor abilities; however, GAL-tg mice showed selective performance deficits on the Morris spatial navigational task and the social transmission of food preference olfactory memory test. These results suggest that elevated expression of galanin contributes to the neurochemical and cognitive impairments characteristic of AD.

Galanin-Like Peptide (GALP) Is a Target for Regulation by Leptin in the Hypothalamus of the Rat

Galanin-like peptide (GALP), which was recently isolated from the porcine hypothalamus, shares sequence homology with galanin and binds with high affinity to galanin receptors. To study the distribution and regulation of GALP-expressing cells in the brain, we cloned a 120 base-pair cDNA fragment of rat GALP and produced an antisense riboprobe. In situ hybridization for GALP mRNA was then performed on tissue sections throughout the forebrain of adult ovariectomized female rats. We found GALP mRNA-containing cells in the arcuate nucleus (Arc), caudal dorsomedial nucleus, median eminence and the pituitary. Because GALP mRNA in the Arc appeared to overlap with the known distribution of leptin receptor mRNA, we tested the hypothesis that GALP expression is regulated by leptin. Using in situ hybridization, we compared the number of GALP mRNA-containing cells among groups of rats that were fed ad lib or fasted for 48 h and treated with either leptin or vehicle. Fasting reduced the number of identifiable cells co...

AZD2184: a radioligand for sensitive detection of β-amyloid deposits

The presence of β‐amyloid plaques in brain is a hallmark of Alzheimer’s disease (AD) and serves as a biomarker for confirmation of diagnosis postmortem. Positron emission tomography (PET) radioligands such as Pittsburgh compound B ([11C]‐2‐(3‐fluoro‐4‐methylamino‐phenyl)‐benzothiazol‐6‐ol) (PIB) binds selectively to β‐amyloid and are promising new tools supporting the clinical diagnoses of AD. In addition, such methodology may be useful for evaluation of new drugs aiming at reduction of amyloid plaque load. The objective of this study is to develop a new amyloid selective PET radioligand with higher signal‐to‐background ratio when compared with existing amyloid PET ligands. The lead compound, AZD2184, (2‐[6‐(methylamino)pyridin‐3‐yl]‐1,3‐benzothiazol‐6‐ol) was found to have high affinity for amyloid fibrils in vitro (Kd: 8.4 ± 1.0 nM). Two minutes after i.v. administration in rats, about 1% of the dose was in brain. In vitro autoradiography on cortical brain sections from amyloid‐beta precursor protein/presenilin 1 (APP/PS1) mice and AD patients showed that while [3H]AZD2184 and [3H]PIB are mutually displaceable, [3H]AZD2184 displays a higher signal‐to‐background ratio primarily by virtue of lower background binding levels. The ratio of binding ability in prefrontal cortex (high plaque load) to subcortical white matter (background) was 4.5 for [3H]AZD2184 and 0.8 for [3H]PIB at 1 nM. In adjacent cortical sections from APP/PS1 mouse as well as from AD cortical tissue, [3H]AZD2184 and antibodies to human β‐amyloid labeled identical structures. In vivo administration of [3H]AZD2184 to APP/PS1 mice further showed that [3H]AZD2184 labels amyloid deposits with low non‐specific background binding. Taken together, the pre‐clinical profile of AZD2184 in relation to the reference ligand PIB, suggests that 11C‐labeled AZD2184 is a potential radioligand for PET‐visualization of β‐amyloid deposits in the living human brain.

Characterization of AZD4694, a novel fluorinated Abeta plaque neuroimaging PET radioligand

J. Neurochem. (2010) 114, 784–794.

Distribution and Regulation of Galanin-Like Peptide (GALP) in the Hypothalamus of the Mouse

Galanin-like peptide (GALP) is a newly discovered molecule whose expression in the brain is confined to the arcuate nucleus and median eminence. In the rat, cellular levels of GALP mRNA are reduced by fasting and reversed by peripheral administration of leptin. The purpose of this investigation was 1) to clone and map the distribution of GALP mRNA in the brain of the mouse; 2) to compare the pattern and magnitude of GALP mRNA expression in the leptin-deficient obese (ob/ob) mouse with that of wild-type controls; and 3) to examine the effects of leptin delivered into the brain on the expression of GALP mRNA in the ob/ob mouse. We report the sequence of a mouse GALP cDNA and show that GALP mRNA is expressed in the arcuate nucleus, median eminence, infundibular stalk, and the neurohypophysis of this species. The expression of GALP mRNA in the brain was markedly reduced in the ob/ob mice, compared with wild-type animals. Intracerebroventricular infusion of leptin to ob/ob mice increased both the number of GALP mRNA-expressing neurons and their content of GALP mRNA, compared with vehicle-treated controls. These observations demonstrate that GALP mRNA is induced by leptin through a direct action on the brain.

First and Second Generation γ-Secretase Modulators (GSMs) Modulate Amyloid-β (Aβ) Peptide Production through Different Mechanisms

Background: γ-Secretase modulators (GSMs) hold potential as disease modifiers in Alzheimer disease; however, their mechanism of action is not completely understood. Results: Second generation in vivo active GSMs were described and shown to modulate Aβ production via a non-APP targeting mechanism, different from the NSAIDs class of GSMs. Conclusion: A growing class of second generation GSMs appears to target γ-secretase and displays a different mechanism of action compared with first generation GSMs. Significance: The identification of in vivo active non-APP targeting second generation GSMs may facilitate the development of novel therapeutics against AD. γ-Secretase-mediated cleavage of amyloid precursor protein (APP) results in the production of Alzheimer disease-related amyloid-β (Aβ) peptides. The Aβ42 peptide in particular plays a pivotal role in Alzheimer disease pathogenesis and represents a major drug target. Several γ-secretase modulators (GSMs), such as the nonsteroidal anti-inflammatory drugs (R)-flurbiprofen and sulindac sulfide, have been suggested to modulate the Alzheimer-related Aβ production by targeting the APP. Here, we describe novel GSMs that are selective for Aβ modulation and do not impair processing of Notch, EphB2, or EphA4. The GSMs modulate Aβ both in cell and cell-free systems as well as lower amyloidogenic Aβ42 levels in the mouse brain. Both radioligand binding and cellular cross-competition experiments reveal a competitive relationship between the AstraZeneca (AZ) GSMs and the established second generation GSM, E2012, but a noncompetitive interaction between AZ GSMs and the first generation GSMs (R)-flurbiprofen and sulindac sulfide. The binding of a 3H-labeled AZ GSM analog does not co-localize with APP but overlaps anatomically with a γ-secretase targeting inhibitor in rodent brains. Combined, these data provide compelling evidence of a growing class of in vivo active GSMs, which are selective for Aβ modulation and have a different mechanism of action compared with the original class of GSMs described.

Distribution and regulation of galanin receptor 1 messenger RNA in the forebrain of wild type and galanin-transgenic mice.

To learn more about molecular alterations in the brain that occur as a consequence of either the chronic excess or absence of peptide neurotransmitters, we examined the impact of genetically manipulating the neuropeptide galanin on the expression of one of its cognate receptors, galanin receptor 1. First, we examined the distribution of galanin receptor 1 messenger RNA in the mouse forebrain, and found it to be abundantly expressed in many brain regions, including in numerous hypothalamic and other forebrain regions associated with neuroendocrine function. The distribution of galanin receptor 1 messenger RNA in the mouse was similar to previous reports in the rat, with additional expression noted in the caudate putamen and in several midbrain regions. Next, using quantitative in situ hybridization, we measured cellular levels of galanin receptor 1 messenger RNA in the brains of mice that either overexpress galanin (galanin transgenic) or lack a functional galanin gene (galanin knockout). We report that relative to wild-type controls, the expression of galanin receptor 1 messenger RNA was increased in discrete areas of the brain in galanin-transgenic mice, but that depletion of galanin/noradrenergic innervation to the hypothalamus with the neurotoxin 6-hydroxydopamine did not alter levels of galanin receptor 1 messenger RNA. We also report that levels of galanin receptor 1 messenger RNA were not different between galanin-knockout and wild-type mice. These results suggest that compensatory adjustments in the expression of cognate receptors represent one mechanism by which the developing nervous system attempts to maintain homeostasis in response to overexpression of a peptidergic transmitter. However, the lack of significant changes in galanin receptor 1 messenger RNA in galanin-knockout mice suggests that developmentally programmed levels of receptor expression are maintained even in the complete absence of ligand.

Distribution of the voltage‐gated sodium channel Nav1.7 in the rat: Expression in the autonomic and endocrine systems

It is generally accepted that the voltage‐gated, tetrodotoxin‐sensitive sodium channel, NaV1.7, is selectively expressed in peripheral ganglia. However, global deletion in mice of NaV1.7 leads to death shortly after birth (Nassar et al. [ 2004 ] Proc. Natl. Acad. Sci. U. S. A. 101:12706–12711), suggesting that this ion channel might be more widely expressed. To understand better the potential physiological function of this ion channel, we examined NaV1.7 expression in the rat by in situ hybridization and immunohistochemistry. As expected, highest mRNA expression levels are found in peripheral ganglia, and the protein is expressed within these ganglion cells and on the projections of these neurons in the central nervous system. Importantly, we found that NaV1.7 is present in discrete rat brain regions, and the unique distribution pattern implies a central involvement in endocrine and autonomic systems as well as analgesia. In addition, NaV1.7 expression was detected in the pituitary and adrenal glands. These results indicate that NaV1.7 is not only involved in the processing of sensory information but also participates in the regulation of autonomic and endocrine systems; more specifically, it could be implicated in such vital functions as fluid homeostasis and cardiovascular control. J. Comp. Neurol. 504:680–689, 2007.

Differential regulation of adenylate cyclase activity in rat ventral and dorsal hippocampus by rat galanin

Rat galanin inhibits basal as well as forskolin-stimulated adenylate cyclase activity in rat ventral and dorsal hippocampus. The inhibition of adenylate cyclase activity, both basal and forskolin-stimulated, is characterised by IC50 values being 250-fold lower in ventral hippocampus (IC50 = 1.1 nM) compared to the dorsal hippocampus (IC50 = 270 nM). The maximal inhibition of basal and forskolin-stimulated adenylate cyclase activity in both ventral and dorsal hippocampus in the presence of 10 microM rat galanin is 34-45%. The analysis of the binding data obtained with 125I-labelled Tyr26-porcine galanin as a tracer reveals similar binding constants for rat galanin in both ventral and dorsal hippocampus with 4.8-fold higher concentration of galanin receptors in the ventral hippocampus. Putative galanin receptor subtype differences between the ventral and dorsal hippocampus have been noted by Hedlund et al. (Eur. J. Pharmacol., 224 (1992) 203-205). This study yields further confirmation for the existence of different galanin receptor subtypes or for differential coupling of galanin receptors to the adenylate cyclase in the dorsal versus ventral hippohampus.

Alzheimer's Disease: Presenilin 2-Sparing γ-Secretase Inhibition Is a Tolerable Aβ Peptide-Lowering Strategy

γ-Secretase inhibition represents a major therapeutic strategy for lowering amyloid β (Aβ) peptide production in Alzheimers disease (AD). Progress toward clinical use of γ-secretase inhibitors has, however, been hampered due to mechanism-based adverse events, primarily related to impairment of Notch signaling. The γ-secretase inhibitor MRK-560 represents an exception as it is largely tolerable in vivo despite displaying only a small selectivity between Aβ production and Notch signaling in vitro. In exploring the molecular basis for the observed tolerability, we show that MRK-560 displays a strong preference for the presenilin 1 (PS1) over PS2 subclass of γ-secretases and is tolerable in wild-type mice but causes dose-dependent Notch-related side effect in PS2-deficient mice at drug exposure levels resulting in a substantial decrease in brain Aβ levels. This demonstrates that PS2 plays an important role in mediating essential Notch signaling in several peripheral organs during pharmacological inhibition of PS1 and provide preclinical in vivo proof of concept for PS2-sparing inhibition as a novel, tolerable and efficacious γ-secretase targeting strategy for AD.