MiRNA-34 and stress response

Psychiatric disorders are known to result from a strong interaction between genetic predisposition and environmental factors, mainly exposure to stressful events. Environmental events can modulate genes expression, possibly via epigenetic mechanisms, and affect onset/expression of a disease [1]. Epigenetic mechanisms include, among others, post-transcriptional regulation by non-coding RNAs such as microRNAs (miRNAs). MiRNAs are small non-coding RNAs predicted to regulate hundreds of targets and to be engaged in every biological process [2]. Thanks to their ability to fine-tune gene expression, miRNAs can control gene expression patterns favoring organism’s adaptation to internal and environmental (external) factors [3], such as stressful events

Strain-dependent differences in corticolimbic processing of aversive or rewarding stimuli

Aberrations in the elaboration of both aversive and rewarding stimuli characterize several psychopathologies including anxiety, depression and addiction. Several studies suggest that different neurotrasmitters, within the corticolimbic system, are critically involved in the processing of positive and negative stimuli. Individual differences in this system, depending on genotype, have been shown to act as a liability factor for different psychopathologies. Inbred mouse strains are commonly used in preclinical studies of normal and pathological behaviors. In particular, C57BL/6J (C57) and DBA/2J (DBA) strains have permitted to disclose the impact of different genetic backgrounds over the corticolimbic system functions. Here, we summarize the main findings collected over the years in our laboratory, showing how the genetic background plays a critical role in modulating amminergic and GABAergic neurotransmission in prefrontal-accumbal-amygdala system response to different rewarding and aversive experiences, as well as to stress response. Finally, we propose a top-down model for the response to rewarding and aversive stimuli in which amminergic transmission in prefrontal cortex (PFC) controls accumbal and amygdala neurotransmitter response

The Key Role of the Amygdala in Stress

Several data highlighted that stress exposure is strongly associated with several psychiatric disorders. The amygdala, an area of the brain that contributes to emotional processing, has a pivotal role in psychiatric disorders and it has been demonstrated to be highly responsive to stressful events. Here we will review evidences indicating how the amygdala changes its functionality following exposure to stress and how this contributes to the onset of anxiety disorders

Strain-dependent variations in stress coping behavior are mediated by a 5-HT/GABA interaction within the prefrontal corticolimbic system

Background: Serotonin and γ- Aminobutyric acid (GABA) transmission is crucial in coping strategies. Methods: Here, using mice from 2 inbred strains widely exploited in behavioral neurochemistry, we investigated whether serotonin transmission in medial prefrontal cortex and GABA in basolateral amygdala determine strain-dependent liability to stress response and differences in coping. Results: C57BL/6J mice displayed greater immobility in the forced swimming test, higher serotonin outflow in medial prefrontal cortex, higher GABA outflow in basolateral amygdala induced by stress, and higher serotonin 1A receptor levels in medial prefrontal cortex accompanied by lower GABAb receptor levels in basolateral amygdala than DBA/2J mice. In assessing whether serotonin in medial prefrontal cortex determines GABA functioning in response to stress and passive coping behavior in C57BL/6J and DBA/2J mice, we observed that selective prefrontal serotonin depletion in C57BL/6J and DBA/2J reduced stress-induced GABA outflow in basolateral amygdala and immobility in the forced swimming test. Conclusions: These results show that strain-dependent prefrontal corticolimbic serotonin/GABA regulation determines the strain differences in stress-coping behavior in the forced swimming test and point to a role of a specific neuronal system in genetic susceptibility to stress that opens up new prospects for innovative therapies for stress disorders

Cerebellar BDNF promotes exploration and seeking for novelty

Approach system considered a motivational system that activates reward-seeking behavior is associated with exploration/impulsivity, whereas avoidance system considered an attentional system that promotes inhibition of appetitive responses is associated with active overt withdrawal. Approach and avoidance dispositions are modulated by distinct neurochemical profiles and synaptic patterns. However, the precise working of neurons and trafficking of molecules in the brain activity predisposing to approach and avoidance are yet unclear

Effects of lack of microRNA-34 on the neural circuitry underlying the stress response and anxiety

Stress-related psychiatric disorders, including anxiety, are complex diseases that have genetic, and environmental causes. Stressful experiences increase the release of prefrontal amygdala neurotransmitters, a response that is relevant to cognitive, emotional, and behavioral coping. Moreover, exposure to stress elicits anxiety-like behavior and dendritic remodeling in the amygdala. Members of the miR-34 family have been suggested to regulate synaptic plasticity and neurotransmission processes, which mediate stress-related disorders. Using mice that harbored targeted deletions of all 3 members of the miR-34-family (miR-34-TKO), we evaluated acute stress-induced basolateral amygdala (BLA)-GABAergic and medial prefrontal cortex (mpFC) aminergic outflow by intracerebral in vivo microdialysis. Moreover, we also examined fear conditioning/extinction, stress-induced anxiety, and dendritic remodeling in the BLA of stress-exposed TKO mice. We found that TKO mice showed resilience to stress-induced anxiety and facilitation in fear extinction. Accordingly, no significant increase was evident in aminergic prefrontal or amygdala GABA release, and no significant acute stress-induced amygdalar dendritic remodeling was observed in TKO mice. Differential GRM7, 5-HT2C, and CRFR1 mRNA expressionwas noted in the mpFC and BLA between TKO andWT mice. Our data demonstrate that the miR-34 has a critical function in regulating the behavioral and neurochemical response to acute stress and in inducing stress-related amygdala neuroplasticity

Unbalance between Excitation and Inhibition in Phenylketonuria, a Genetic Metabolic Disease Associated with Autism

Phenylketonuria (PKU) is the most common genetic metabolic disease with a well-documented association with autism spectrum disorders. It is characterized by the deficiency of the phenylalanine hydroxylase activity, causing plasmatic hyperphenylalaninemia and variable neurological and cognitive impairments. Among the potential pathophysiological mechanisms implicated in autism spectrum disorders is the excitation/inhibition (E/I) imbalance which might result from alterations in excitatory/inhibitory synapse development, synaptic transmission and plasticity, downstream signalling pathways, and intrinsic neuronal excitability. Here, we investigated functional and molecular alterations in the prefrontal cortex (pFC) of BTBR-Pah(enu2) (ENU2) mice, the animal model of PKU. Our data show higher frequency of inhibitory transmissions and significant reduced frequency of excitatory transmissions in the PKU-affected mice in comparison to wild type. Moreover, in the pFC of ENU2 mice, we reported higher levels of the post-synaptic cell-adhesion proteins neuroligin1 and 2. Altogether, our data point toward an imbalance in the E/I neurotransmission favouring inhibition in the pFC of ENU2 mice, along with alterations of the molecular components involved in the organization of cortical synapse. In addition to being the first evidence of E/I imbalance within cortical areas of a mouse model of PKU, our study provides further evidence of E/I imbalance in animal models of pathology associated with autism spectrum disorders

Mouse model of panic disorder: Vulnerability to early environmental instability is strain-dependent.

AbstractEarly life experiences and genetic background shape phenotypic variation. Several mouse models based on early treatments have evaluated short‐ and long‐term phenotypic alterations and explored their molecular mechanisms. The instability of maternal cues was used to model human separation anxiety in outbred mice, one of the etiopathogenetic factors that predict panic disorder (PD). Application of the repeated cross‐fostering (RCF) protocol to inbred strains (C57 and DBA) allowed us to measure differential responses to the same experimental manipulation. Ultrasounds emitted during isolation indicated that after RCF, pups from both strains lose their ability to be comforted by nest cues, but the frequency modulation of separation calls increased in RCF‐C57 and decreased in RCF‐DBA mice. No strain‐specific difference in olfactory ability explained these responses in RCF‐exposed mice. Rather, disruption of the infant‐mother bond may differentially affect separation calls in the two strains. Moreover, the RCF‐associated increased respiratory response to hypercapnia–an endophenotype of human PD documented among mice outbred strains–was replicated in the C57 strain only. We suggest that RCF‐induced instability of the early environment affects emotionality and respiratory physiology differentially, depending on pups' genetic background. These strain‐specific responses provide a lead to understand differential vulnerability to emotional disorders

Decline of cardiomyocyte contractile performance and bioenergetic function in socially stressed male rats

Chronic social stress has been epidemiologically linked to increased risk for cardiovascular disease, yet the underlying pathophysiological mechanisms are still largely elusive. Mitochondrial (dys)function represents a potential intersection point between social stress exposure and (mal)adaptive cardiac responses. In this study, we used a rodent model of social stress to study the extent to which alterations in the cellular mechanical properties of the heart were associated with changes in indexes of mitochondrial function. Male adult rats were exposed to repeated episodes of social defeat stress or left undisturbed (controls). ECG signals were recorded during and after social defeat stress. Twenty-four hours after the last social defeat, cardiomyocytes were isolated for analyses of mechanical properties and intracellular Ca(2+) dynamics, mitochondrial respiration, and ATP content. Results indicated that social defeat stress induced potent cardiac sympathetic activation that lasted well beyond stress exposure. Moreover, cardiomyocytes of stressed rats showed poor contractile performance (e.g., slower contraction and relaxation rates) and intracellular Ca(2+) derangement (e.g., slower Ca(2+) clearing), which were associated with indexes of reduced reserve respiratory capacity and decreased ATP production. In conclusion, this study suggests that repeated social stress provokes impaired cardiomyocyte contractile performance and signs of altered mitochondrial bioenergetics in the rat heart. Future studies are needed to clarify the causal link between cardiac and mitochondrial functional remodeling under conditions of chronic social stress

Elevated miR-34a expression and altered transcriptional profile are associated with adverse electromechanical remodeling in the heart of male rats exposed to social stress.

This study investigated epigenetic risk factors that may contribute to stress-related cardiac disease in a rodent model. Experiment 1 was designed to evaluate the expression of microRNA-34a (miR-34a), a known modulator of both stress responses and cardiac pathophysiology, in the heart of male adult rats exposed to a single or repeated episodes of social defeat stress. Moreover, RNA sequencing was conducted to identify transcriptomic profile changes in the heart of repeatedly stressed rats. Experiment 2 was designed to assess cardiac electromechanical changes induced by repeated social defeat stress that may predispose rats to cardiac dysfunction. Results indicated a larger cardiac miR-34a expression after repeated social defeat stress compared to a control condition. This molecular modification was associated with increased vulnerability to pharmacologically induced arrhythmias and signs of systolic left ventricular dysfunction. Gene expression analysis identified clusters of differentially expressed genes in the heart of repeatedly stressed rats that are mainly associated with morphological and functional properties of the mitochondria and may be directly regulated by miR-34a. These results suggest the presence of an association between miR-34a overexpression and signs of adverse electromechanical remodeling in the heart of rats exposed to repeated social defeat stress, and point to compromised mitochondria efficiency as a potential mediator of this link. This rat model may provide a useful tool for investigating the causal relationship between miR-34a expression, mitochondrial (dys)function, and cardiac alterations under stressful conditions, which could have important implications in the context of stress-related cardiac disease