Luigi Bellocchio

Mutations in the synaptic scaffold protein SHANK3 represent one of the most frequent genetic causes of autism spectrum disorder (ASD), yet the circuit mechanisms through which SHANK3 dysfunction leads to behavioral alterations remain incompletely understood. The anterior insular cortex (aINS) is a key integrative hub involved in socio-emotional processing, anxiety regulation, and social cognition, a group of behaviors frequently disrupted in ASD. Here, we investigated whether selective deletion of SHANK3 signaling in glutamatergic neurons of the aINS is sufficient to produce ASD-relevant behavioral and circuit phenotypes. Using conditional Shank3 ^flox4-22 mice combined with stereotaxic viral delivery of Cre recombinase under the CaMKII promoter, we selectively deleted Shank3 in glutamatergic neurons of the aINS. Behavioral phenotyping revealed increased anxiety-like behavior, enhanced repetitive behavior, and impaired social memory, while sociability and locomotor activity were largely preserved. These behavioral alterations were accompanied by genotype-dependent differences in neuronal activity revealed by calcium imaging, indicating disrupted activity dynamics in insular glutamatergic neurons following Shank3 deletion. To assess the broader relevance of these findings, we evaluated the behavioral profile of BTBR T+ Itpr3tf/J mice, a model of idiopathic ASD, in the same battery of behavioral tests. Several behavioral alterations observed following insular Shank3 deletion partially overlapped with those present in BTBR mice, supporting the relevance of aINS Shank3 in ASD-related phenotypes. Together, these findings identify glutamatergic neurons of the aINS as a critical locus through which Shank3 dysfunction can disrupt socio-emotional, cognitive, and repetitive behaviors. Our results highlight the aINS as a key circuit node contributing to ASD-related behavioral alterations and provide mechanistic insight into how synaptic scaffold disruption leads to circuit dysfunction and produces behavioral alterations.

Many brain disorders involve mitochondrial alterations, but owing to the lack of suitable tools, the causal role of mitochondrial dysfunction in pathophysiological processes is difficult to establish. Heterotrimeric guanine nucleotide-binding (G) proteins are key regulators of cell functions, and they can be found within mitochondria. Therefore, we reasoned that the activation of stimulatory mitochondrial G proteins (G_s) could rapidly promote the activity of the organelle and possibly compensate for bioenergetic dysfunction. Here, we show that a mitochondria-targeted recombinant designer receptor exclusively activated by designer drugs (mitoDREADD-G_s) can acutely trigger intramitochondrial signaling to increase mitochondrial membrane potential and oxygen consumption. In vivo activation of mitoDREADD-G_s abolished memory alterations in cannabinoid-treated mice and in two mouse models of Alzheimer's disease and frontotemporal dementia. Thus, mitoDREADD-G_s enables the establishment of causal relationships between mitochondria and biological or disease-related processes and represents an innovative potential therapeutic approach for disorders associated with mitochondrial impairment.

The Nucleus Accumbens (NAc) is a critical brain region for the effects of psychostimulant drugs. Type‐1 cannabinoid receptors (CB₁), the main elements of the endocannabinoid system (ECS) in the brain, participate in these effects and modulate synaptic functions in the NAc. Besides their neuronal expression, CB₁ receptors are also present in astrocytes, where they contribute to the regulation of synaptic plasticity and behavior. However, the impact of astroglial CB₁ receptors on synaptic plasticity in the NAc and on psychostimulant‐induced synaptic and behavioral effects is currently unknown. This study shows that the psychostimulant amphetamine impairs a form of astroglial CB₁ receptor‐dependent synaptic plasticity in the NAc of male, but not female mice. Consistently, locomotor effects of amphetamine require astroglial CB₁ receptors in male, but not female mice. These results, by revealing unforeseen mechanisms underlying sex‐dependent effects of amphetamine, pave the way to a better understanding of the diverse impact of psychostimulants in women and men.

Administration of Δ ⁹ -tetrahydrocannabinol (THC), the main psychoactive component of the plant Cannabis sativa , can induce psychotic symptomatology in humans and a large spectrum of acute psychotic-like behaviors in mice, including hyperlocomotion observed at low dose of THC (0.3 mg/kg). The cellular and molecular substrates of this effect have not been fully identified yet. Here we demonstrate that THC-induced hyperlocomotion depends on plasma membrane CB1R, which regulate the β-arrestin 1/Akt/GSK3β signaling pathway in D2R-positive neurons of the dorsal striatum forming the striatopallidal pathway of the basal ganglia. Pregnenolone (PREG) and its clinically developed analog, AEF0117, which are signaling specific inhibitors of CB1R (CB1-SSi), prevented GSK3β-dependent psychomotor stimulation induced by THC. Overall, this work highlights a novel intracellular mechanism of CB1R, thereby revealing a neuronal pathway underlying an important but still underexplored effect of THC and cannabis consumption, which could help the development of innovative therapeutic concepts against psychotic conditions.

Growth-associated protein of 43 kDa (GAP43) is a key cytoskeleton-associated component of the presynaptic terminal that facilitates neuroplasticity. Downregulation of GAP43 expression has been associated to various psychiatric conditions in humans and evokes hippocampus-dependent memory impairments in mice. Despite the extensive studies conducted on hippocampal GAP43 in past decades, however, very little is known about its roles in modulating the excitatory versus inhibitory balance in other brain regions. We recently generated conditional knock-out mice in which theGap43gene was selectively inactivated in either telencephalic glutamatergic neurons (Gap43^fl/fl;Nex1^Cremice, hereafter Glu-GAP43^−/−mice) or forebrain GABAergic neurons (Gap43^fl/fl;Dlx5/6^Cremice, hereafter GABA-GAP43^−/−mice). Here, we show that Glu-GAP43^−/−but not GABA-GAP43^−/−mice of either sex show a striking hyperactive phenotype when exposed to a novel environment. This behavioral alteration of Glu-GAP43^−/−mice was linked to a selective activation of dorsal-striatum neurons, as well as to an enhanced corticostriatal glutamatergic transmission and an abrogation of corticostriatal endocannabinoid-mediated long-term depression. In line with these observations, GAP43 was abundantly expressed in corticostriatal glutamatergic terminals of wild-type mice. The novelty-induced hyperactive phenotype of Glu-GAP43^−/−mice was abrogated by chemogenetically inhibiting corticostriatal afferences with a G_i-coupled “designer receptor exclusively activated by designer drugs” (DREADDs), thus further supporting that novelty-induced activity is controlled by GAP43 at corticostriatal excitatory projections. Taken together, these findings show an unprecedented regulatory role of GAP43 in the corticostriatal circuitry and provide a new mouse model with a delimited neuronal-circuit alteration for studying novelty-induced hyperactivity, a phenotypic shortfall that occurs in diverse psychiatric diseases.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and transmission are generally known to be produced by respiratory droplets and aerosols from the oral cavity (O.C.) of infected subjects, as stated by the World Health Organization. Saliva also retains the viral particles and aids in the spread of COVID-19. Angiotensin-converting enzyme Type 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) are two of the numerous factors that promote SARS-CoV-2 infection, expressed by O.C. structures, various mucosa types, and the epithelia of salivary glands. A systemic SARS-CoV-2 infection might result from viral replication in O.C. cells. On the other hand, cellular damage of different subtypes in the O.C. might be associated with various clinical signs and symptoms. Factors interfering with SARS-CoV-2 infection potential might represent fertile ground for possible local pharmacotherapeutic interventions, which may confine SARS-CoV-2 virus entry and transmission in the O.C., finally representing a way to reduce COVID-19 incidence and severity.