Ivana D'Andrea

Hypertension Induces Brain β-Amyloid Accumulation, Cognitive Impairment, and Memory Deterioration Through Activation of Receptor for Advanced Glycation End Products in Brain Vasculature

Although epidemiological data associate hypertension with a strong predisposition to develop Alzheimer disease, no mechanistic explanation exists so far. We developed a model of hypertension, obtained by transverse aortic constriction, leading to alterations typical of Alzheimer disease, such as amyloid plaques, neuroinflammation, blood-brain barrier dysfunction, and cognitive impairment, shown here for the first time. The aim of this work was to investigate the mechanisms involved in Alzheimer disease of hypertensive mice. We focused on receptor for advanced glycation end products (RAGE) that critically regulates A&bgr; transport at the blood-brain barrier and could be influenced by vascular factors. The hypertensive challenge had an early and sustained effect on RAGE upregulation in brain vessels of the cortex and hippocampus. Interestingly, RAGE inhibition protected from hypertension-induced Alzheimer pathology, as showed by rescue from cognitive impairment and parenchymal A&bgr; deposition. The increased RAGE expression in transverse aortic coarctation mice was induced by increased circulating advanced glycation end products and sustained by their later deposition in brain vessels. Interestingly, a daily treatment with an advanced glycation end product inhibitor or antioxidant prevented the development of Alzheimer traits. So far, Alzheimer pathology in experimental animal models has been recognized using only transgenic mice overexpressing amyloid precursor. This is the first study demonstrating that a chronic vascular insult can activate brain vascular RAGE, favoring parenchymal A&bgr; deposition and the onset of cognitive deterioration. Overall we demonstrate that RAGE activation in brain vessels is a crucial pathogenetic event in hypertension-induced Alzheimer disease, suggesting that inhibiting this target can limit the onset of vascular-related Alzheimer disease.

Early social enrichment augments adult hippocampal BDNF levels and survival of BrdU-positive cells while increasing anxiety- and “depression”-like behavior

Early experiences affect brain function and behavior at adulthood. Being reared in a communal nest (CN), consisting of a single nest where three mothers keep their pups together and share care‐giving behavior from birth to weaning (postnatal day [PND] 25), provides an highly socially stimulating environment to the developing pup. Communal nest characterizes the natural ecologic niche of many rodent species including the mouse. At adulthood, CN reared mice, compared to mice reared in standard nesting laboratory condition (SN), show an increase in BDNF protein levels and longer survival of BrdU‐positive cells in the hippocampus. Open field and elevated plus maze results indicate that CN mice, although showing levels of exploratory and locomotor activity similar to those of SN mice, displayed increased anxiety‐like behavior, performing more thigmotaxis in the open field and spending less time in the open arms of the plus maze. Furthermore, CN mice displayed higher levels of immobility behavior in the forced swim test. Overall, these findings show that CN, an highly stimulating early social environment, increases adult neuronal plasticity, as suggested by high BDNF levels and augmented number of newly generated cells in the hippocampus, which is associated to an increased anxiety‐ and “depression”‐like behavior. These findings are discussed in the framework of the neurotrophin hypothesis of depression.

Nonmotor symptoms in Parkinson's disease: Investigating early-phase onset of behavioral dysfunction in the 6-hydroxydopamine-lesioned rat model

To investigate the psychiatric symptoms accompanying the early phases of Parkinsons disease (PD), we injected adult rats with 10.5 μg 6‐hydroxydopamine (6‐OHDA) bilaterally into the dorsal striatum. The resulting neurodegeneration led, 12 weeks after injection, to a mild (36%) reduction of striatal dopamine. We tested the behavioral response of sham and 6‐OHDA‐lesioned animals at different time points after injection to evaluate the onset and progression of behavioral abnormalities. The results showed that such a mild reduction of dopamine levels was associated with a decrease in anxiety‐like behavior, an increase in “depression”‐like behavior, and a marked change in social behavior. Learning and memory abilities were not affected. Overall, the PD rat model used here displays behavioral alterations having face validity with psychiatric symptoms of the pathology and thus appears to be a valuable tool for investigating the neural bases of the early phases of PD.

CX3CR1 Deficiency Alters Hippocampal-Dependent Plasticity Phenomena Blunting the Effects of Enriched Environment

In recent years several evidence demonstrated that some features of hippocampal biology, like neurogenesis, synaptic transmission, learning, and memory performances are deeply modulated by social, motor, and sensorial experiences. Fractalkine/CX3CL1 is a transmembrane chemokine abundantly expressed in the brain by neurons, where it modulates glutamatergic transmission and long-term plasticity processes regulating the intercellular communication between glia and neurons, being its specific receptor CX3CR1 expressed by microglia. In this paper we investigated the role of CX3CL1/CX3CR1 signaling on experience-dependent hippocampal plasticity processes. At this aim wt and CX3CR1GFP/GFP mice were exposed to long-lasting-enriched environment (EE) and the effects on hippocampal functions were studied by electrophysiological recordings of long-term potentiation of synaptic activity, behavioral tests of learning and memory in the Morris water maze paradigm and analysis of neurogenesis in the subgranular zone of the dentate gyrus (DG). We found that CX3CR1 deficiency increases hippocampal plasticity and spatial memory, blunting the potentiating effects of EE. In contrast, exposure to EE increased the number and migration of neural progenitors in the DG of both wt and CX3CR1GFP/GFP mice. These data indicate that CX3CL1/CX3CR1-mediated signaling is crucial for a normal experience-dependent modulation of hippocampal functions.

Role of neuroinflammation in hypertension-induced brain amyloid pathology

Hypertension and sporadic Alzheimers disease (AD) have been associated but clear pathophysiological links have not yet been demonstrated. Hypertension and AD share inflammation as a pathophysiological trait. Thus, we explored if modulating neuroinflammation could influence hypertension-induced β-amyloid (Aβ) deposition. Possible interactions among hypertension, inflammation and Aβ-deposition were studied in hypertensive mice with transverse aortic coarctation (TAC). Given that brain Aβ deposits are detectable as early as 4 weeks after TAC, brain pathology was analyzed in 3-week TAC mice, before Aβ deposition, and at a later time (8-week TAC mice). Microglial activation and interleukin (IL)-1β upregulation were already found in 3-week TAC mice. At a later time, along with evident Aβ deposition, microglia was still activated. Finally, immune system stimulation (LPS) or inhibition (ibuprofen), strategies described to positively or negatively modulate neuroinflammation, differently affected Aβ deposition. We demonstrate that hypertension per se triggers neuroinflammation before Aβ deposition. The finding that only immune system activation, but not its inhibition, strongly reduced amyloid burden suggests that stimulating inflammation in the appropriate time window may represent a promising strategy to limit vascular-triggered AD-pathology.

Communal nesting, an early social enrichment, affects social competences but not learning and memory abilities at adulthood.

We exposed mouse pups to an early social enrichment, the communal nest (CN), to study the effects of the early social experiences on adult brain function and behavior. CN, which consists of a single nest where three mothers keep their pups together and share care-giving behavior from birth to weaning (postnatal day 25), mimics the natural ecological niche of the mouse species. In order to better characterize the previously reported effect of CN on social behavior and to evaluate the extent to which the effects of the CN tend to be pervasive across different behavioral competences, we carried out both a detailed analysis of home-cage social behavior, taking into account the time of the day and absence/presence of an established social hierarchy, and of learning and memory abilities in the water maze. Home-cage observations revealed that, when the hierarchy is established, CN mice display higher levels of social investigation behavior, namely allogrooming and allosniffing, compared to mice reared in standard laboratory conditions (SN). However, when exposed to cage cleaning, a stimulus challenging social hierarchy, CN mice display higher levels of offensive behavior. In the water maze test, CN mice showed a performance similar to that of SN mice. Overall, the present findings confirm that CN mice have elaborate social competencies displaying high levels of aggressive behavior when needed to set up or defend their own territory. Furthermore, present data suggest that the early social enrichment specifically affect adult social behavior but not learning and memory abilities.

Striatal 6-OHDA lesion in mice: Investigating early neurochemical changes underlying Parkinson's disease

Early phases of Parkinsons disease (PD) are characterized by a mild reduction of dopamine (DA) in striatum and by emergence of psychiatric disturbances that precede overt motor symptoms. In order to characterize the neurochemical re-arrangements induced by such striatal impairment, we used a mouse model in which a low dose of 6-hydroxydopamine (6-OHDA) was bilaterally injected into the dorsal striatum. These mice showed a DA reduction of about 40% that remained stable up to 12 weeks after injection. This reduction was accompanied by changes in DA metabolite levels, such as HVA, transiently reduced at 4 weeks, and DOPAC, decreased at 12 weeks. No change in the 5-hydroxytryptamine (5-HT) levels was found but the 5-hydroxyindoleacetic acid (5-HIAA)/5-HT ratio was increased at 4 weeks. In addition, at the same time-point, the levels of 15-F(2t)-IsoP, an index of oxidative stress, and of PGE(2), a major product of cyclooxygenase-2, were decreased in different brain areas while BDNF levels were increased. These neurochemical changes were accompanied by altered behavioral responses concerning the emotional reactivity. Overall, the present findings suggest that a change of 5-HT metabolism and a modification of oxidative stress levels may play a role in the early PD degeneration phases.

Not all stressors are equal: Early social enrichment favors resilience to social but not physical stress in male mice

Early experiences profoundly affect the adult coping response to stress and, consequently, adult vulnerability to psychopathologies triggered by stressing conditions, such as major depression. Though studies in animal models have demonstrated that individuals reared in different conditions are differently vulnerable to a stressor of a specific quality, no information is available as to whether such vulnerability differs when facing stressors of different qualities. To this purpose, we reared C57BL/6 male mice either in standard laboratory rearing condition (SN) or in Communal Nest (CN) condition, the latter consisting of a single nest where three mothers keep their pups together and share care-giving behavior until weaning. We scored the amount of interactions with the mother and with peers and found that CN is a form of social enrichment because both these components are significantly increased. At adulthood, we exposed SN and CN mice, for 4 weeks, to either a physical (forced swim) or a social stress (social instability). Immediately before, at week 1 and at week 4 of the stress procedure, corticosterone levels and the hedonic profile were measured. The results show that CN mice are more resilient to social stress than SN mice since they displayed no anhedonia and lower corticosterone levels. By contrast, both experimental groups were similarly vulnerable to physical stress. Overall, our results show that, in male mice, the adult vulnerability to stress changes according to the quality of the stressor, as a function of early experiences. In addition, the stressor to which CN mice are resilient is qualitatively similar to the stimuli they have experienced early on, both concerning the social domain.

Birth spacing in the mouse communal nest shapes adult emotional and social behavior.

The interactions with the mother and with peers are among the most relevant early environmental factors shaping adult brain function and behavior. In order to investigate the role of these factors, we exploited a novel early manipulation, the Communal Nest (CN), consisting in a single nest where three mothers give birth, keep their pups and share care-giving behavior from birth to weaning. In particular, we reared CD-1 swiss mice in three different CN conditions, each one characterized by a different interval between the three deliveries (Birth Spacing) of 3, 5 or 7 days (respectively, CN+/-3, CN+/-5, CN+/-7). Length of birth spacing affected maternal behavior, CN+/-7 pups receiving the highest levels. At adulthood, mice reared in the different conditions showed differences in emotional response and social skills. In the plus maze test, short birth spacing was found to be associated with enhanced emotionality, CN+/-3 mice showing highest levels of anxiety-like responses in the plus maze compared to the other two CN groups. In the social interaction test, the strategies to achieve dominance differed among the three groups. While CN+/-3 mice appeared to have a more aggressive strategy, displaying high levels of attack behavior in the first encounter, CN+/-5 and CN+/-7 mice displayed a more affiliative strategy based on social investigation. Overall, these findings show that birth spacing shapes the early mouse social environment and, in turn, affects the development of social skills and emotional responses.

Lack of kinase-independent activity of PI3Kγ in locus coeruleus induces ADHD symptoms through increased CREB signaling

Although PI3Kγ has been extensively investigated in inflammatory and cardiovascular diseases, the exploration of its functions in the brain is just at dawning. It is known that PI3Kγ is present in neurons and that the lack of PI3Kγ in mice leads to impaired synaptic plasticity, suggestive of a role in behavioral flexibility. Several neuropsychiatric disorders, such as attention‐deficit/hyperactivity disorder (ADHD), involve an impairment of behavioral flexibility. Here, we found a previously unreported expression of PI3Kγ throughout the noradrenergic neurons of the locus coeruleus (LC) in the brainstem, serving as a mechanism that regulates its activity of control on attention, locomotion and sociality. In particular, we show an unprecedented phenotype of PI3Kγ KO mice resembling ADHD symptoms. PI3Kγ KO mice exhibit deficits in the attentive and mnemonic domains, typical hyperactivity, as well as social dysfunctions. Moreover, we demonstrate that the ADHD phenotype depends on a dysregulation of CREB signaling exerted by a kinase‐independent PI3Kγ‐PDE4D interaction in the noradrenergic neurons of the locus coeruleus, thus uncovering new tools for mechanistic and therapeutic research in ADHD.