Inhibition of RPTPβ/ζ reduces chronic ethanol intake in adolescent mice and modulates ethanol effects on hippocampal neurogenesis and glial responses in a sex-dependent manner

Enhanced fear extinction through infralimbic perineuronal net digestion: The modulatory role of adolescent alcohol exposure

Perineuronal nets (PNNs) are specialized components of the extracellular matrix that play a critical role in learning and memory. In a Pavlovian fear conditioning paradigm, degradation of PNNs affects the formation and storage of fear memories. This study examined the impact of adolescent intermittent ethanol (AIE) exposure by vapor inhalation on the expression of PNNs in the adult rat prelimbic (PrL) and infralimbic (IfL) subregions of the medial prefrontal cortex. Results indicated that following AIE, the total number of PNN positive cells in the PrL cortex increased in layer II/III but did not change in layer V. Conversely, in the IfL cortex, the number of PNN positive cells decreased in layer V, with no change in layer II/III. In addition, the intensity of PNN staining was significantly altered by AIE exposure, which narrowed the distribution of signal intensity, reducing the number of high and low intensity PNNs. Given these changes in PNNs, the next experiment assessed the effects of AIE and PNN digestion on extinction of a conditioned fear memory. In Air control rats, digestion of PNNs by bilateral infusion of Chondroitinase ABC (ChABC) into the IfL cortex enhanced fear extinction and reduced contextual fear renewal. In contrast, both fear extinction learning and contextual fear renewal remained unchanged following PNN digestion in AIE exposed rats. These results highlight the sensitivity of prefrontal PNNs to adolescent alcohol exposure and suggest that ChABC-induced plasticity is reduced in the IfL cortex following AIE exposure.

Roles of Oxidative Stress and Autophagy in Alcohol-Mediated Brain Damage

Excessive alcohol consumption significantly impacts human health, particularly the brain, due to its susceptibility to oxidative stress, which contributes to neurodegenerative conditions. Alcohol metabolism in the brain occurs primarily via catalase, followed by CYP2E1 pathways. Excess alcohol metabolized by CYP2E1 generates reactive oxygen/nitrogen species (ROS/RNS), leading to cell injury via altering many different pathways. Elevated oxidative stress impairs autophagic processes, increasing post-translational modifications and further exacerbating mitochondrial dysfunction and ER stress, leading to cell death. The literature highlights that alcohol-induced oxidative stress disrupts autophagy and mitophagy, contributing to neuronal damage. Key mechanisms include mitochondrial dysfunction, ER stress, epigenetics, and the accumulation of oxidatively modified proteins, which lead to neuroinflammation and impaired cellular quality control. These processes are exacerbated by chronic alcohol exposure, resulting in the suppression of protective pathways like NRF2-mediated antioxidant responses and increased susceptibility to neurodegenerative changes in the brain. Alcohol-mediated neurotoxicity involves complex interactions between alcohol metabolism, oxidative stress, and autophagy regulation, which are influenced by various factors such as drinking patterns, nutritional status, and genetic/environmental factors, highlighting the need for further molecular studies to unravel these mechanisms and develop targeted interventions.

Pleiotrophin Overexpression Reduces Adolescent Ethanol Consumption and Modulates Ethanol-Induced Glial Responses and Changes in the Perineuronal Nets in the Mouse Hippocampus

AIMS

To investigate whether pleiotrophin (PTN) overexpression influences ethanol consumption during adolescence and its effects on glial responses, neurogenesis, and perineuronal nets (PNNs) in the mouse hippocampus.

METHODS

Male and female adolescent transgenic mice with elevated PTN levels (Ptn-Tg) and controls underwent an intermittent access to ethanol (IAE) 2-bottle choice protocol. Ethanol consumption, PTN levels, neurogenesis, and glial responses were measured in the hippocampus. Immunohistochemistry was used to assess changes in new neurons, microglial and astrocyte populations, and PNNs.

RESULTS

Ptn-Tg mice consumed significantly less ethanol compared to controls, irrespective of sex. Chronic alcohol exposure reduced PTN levels in the hippocampus. PTN overexpression decreased the number of new neurons in the dentate gyrus (DG) and prevented ethanol-induced microglial activation. Ptn-Tg mice had significantly more astrocytes and fewer PNNs, with a higher percentage of parvalbumin (PV) positive cells surrounded by PNNs under basal conditions. However, ethanol drastically reduced the number of PV+ cells in the DG of Ptn-Tg mice, despite the presence of PNNs.

CONCLUSION

PTN overexpression reduces adolescent ethanol consumption and influences ethanol-induced effects on hippocampal neurogenesis, glial responses, and PNN remodeling. These findings underscore the importance of PTN in modulating alcohol-induced neurotoxicity.

Modulation of stress-, pain-, and alcohol-related behaviors by perineuronal nets

Perineuronal nets (PNNs) are a special form of central nervous system extracellular matrix enriched in hyaluronan, chondroitin sulfate proteoglycans, tenascins, and link proteins that regulate synaptic plasticity. Most PNNs in the brain surround parvalbumin-expressing inhibitory interneurons, which tightly regulate excitatory/inhibitory balance and brain activity associated with optimal cognitive functioning. Alterations in PNNs have been observed in neurological diseases and psychiatric disorders, suggesting that they may be key contributors to the neuropathological progression and behavioral changes in these diseases. Alcohol use disorder (AUD), major depressive disorder (MDD), and chronic pain are highly comorbid conditions, and changes in PNNs have been observed in animal models of these disorders, as well as postmortem tissue from individuals diagnosed with AUD and MDD. This review focuses on the literature describing stress-, alcohol-, and pain-induced adaptations in PNNs, potential cellular contributors to altered PNNs, and the role of PNNs in behaviors related to these disorders. Medicines that can restore PNNs to a non-pathological state may be a novel therapeutic approach to treating chronic pain, AUD, and MDD.

Enhanced Fear Extinction Through Infralimbic Perineuronal Net Digestion: The Modulatory Role of Adolescent Alcohol Exposure

Perineuronal nets (PNNs) are specialized components of the extracellular matrix that play a critical role in learning and memory. In a Pavlovian fear conditioning paradigm, degradation of PNNs affects the formation and storage of fear memories. This study examined the impact of adolescent intermittent ethanol (AIE) exposure by vapor inhalation on the expression of PNNs in the adult rat prelimbic (PrL) and infralimbic (IfL) subregions of the medial prefrontal cortex. Results indicated that following AIE, the total number of PNN positive cells in the PrL cortex increased in layer II/III but did not change in layer V. Conversely, in the IfL cortex, the number of PNN positive cells decreased in layer V, with no change in layer II/III. In addition, the intensity of PNN staining was significantly altered by AIE exposure, which narrowed the distribution of signal intensity, reducing the number of high and low intensity PNNs. Given these changes in PNNs, the next experiment assessed the effects of AIE and PNN digestion on extinction of a conditioned fear memory. In Air control rats, digestion of PNNs by bilateral infusion of Chondroitinase ABC (ChABC) into the IfL cortex enhanced fear extinction and reduced contextual fear renewal. In contrast, both fear extinction learning and contextual fear renewal remained unchanged following PNN digestion in AIE exposed rats. These results highlight the sensitivity of prefrontal PNNs to adolescent alcohol exposure and suggest that ChABC-induced plasticity is reduced in the IfL cortex following AIE exposure.

Adolescent intermittent ethanol exposure decreases perineuronal nets in the hippocampus in a sex dependent manner: Modulation through pharmacological inhibition of RPTPβ/ζ

Adolescence is a critical period for brain maturation in which this organ undergoes critical plasticity mechanisms that increase its vulnerability to the effects of alcohol. Significantly, ethanol-induced disruption of hippocampal neurogenesis has been related to cognitive decline in adulthood. During adolescence, the maturation of perineuronal nets (PNNs), extracellular matrix structures highly affected by ethanol consumption, plays a fundamental role in neurogenesis and plasticity in the hippocampus. Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ is a critical anchor point for PNNs on the cell surface. Using the adolescent intermittent access to ethanol (IAE) model, we previously showed that MY10, a small-molecule inhibitor of RPTPβ/ζ, reduces chronic ethanol consumption in adolescent male mice but not in females and prevents IAE-induced neurogenic loss in the male hippocampus. We have now tested if these effects of MY10 are related to sex-dependent modulatory actions on ethanol-induced effects in PNNs. Our findings suggest a complex interplay between alcohol exposure, neural structures, and sex-related differences in the modulation of PNNs and parvalbumin (PV)-positive cells in the hippocampus. In general, IAE increased the number of PV + cells in the female hippocampus and reduced PNNs intensity in different hippocampal regions, particularly in male mice. Notably, we found that pharmacological inhibition of RPTPβ/ζ with MY10 regulates ethanol-induced alterations of PNNs intensity, which correlates with the protection of hippocampal neurogenesis from ethanol neurotoxic effects and may be related to the capacity of MY10 to increase the gene expression of key components of PNNs.