A Glitch in the Matrix: Aberrant Extracellular Matrix Proteolysis Contributes to Alcohol Seeking

Transcriptome changes in the nucleus of the solitary tract induced by repeated stress, alcohol dependence, or stress-induced drinking in dependent mice

Stress increases alcohol consumption in dependent animals and contributes to the development of alcohol use disorder. The nucleus of the solitary tract (NTS) is a critical brainstem region for integrating and relaying central and peripheral signals to regulate stress responses, but it is not known if it plays a role in alcohol dependence- or in stress-induced escalations in alcohol drinking in dependent mice. Here, we used RNA-sequencing and bioinformatics analyses to study molecular adaptations in the NTS of C57BL/6J male mice that underwent an ethanol drinking procedure that uses exposure to chronic intermittent ethanol (CIE) vapor, forced swim stress (FSS), or both conditions (CIE + FSS). Transcriptome profiling was performed at three different times after the last vapor cycle (0-hr, 72-hr, and 168-hr) to identify changes in gene expression associated with different stages of ethanol intoxication and withdrawal. In the CIE and CIE + FSS groups at 0-hr, there was upregulation of genes enriched for cellular response to type I interferon (IFN) and type I IFN- and cytokine-mediated signaling pathways, while the FSS group showed upregulation of neuronal genes. IFN signaling was the top gene network positively correlated with ethanol consumption levels in the CIE and CIE + FSS groups. Results from different analyses (differential gene expression, weighted gene coexpression network analysis, and rank-rank hypergeometric overlap) indicated that activation of type I IFN signaling would be expected to increase ethanol consumption. The CIE and CIE + FSS groups also shared an immune signature in the NTS as has been demonstrated in other brain regions after chronic ethanol exposure. A temporal-based clustering analysis revealed a unique expression pattern in the CIE + FSS group that suggests the interaction of these two stressors produces adaptations in synaptic and glial functions that may drive stress-induced drinking.

Matrix metalloproteinase-9 overexpression in the hippocampus reduces alcohol-induced conditioned-place preference by regulating synaptic plasticity in mice

Extracellular matrix proteins appear to be necessary for the synaptic plasticity that underlies addiction memory. In the brain, matrix metalloproteinases (MMPs), especially matrix metalloproteinase-9 (MMP-9), have been recently implicated in processes involving alcohol reward and memory. Here, we showed for the first time, the positive effects of MMP-9 on alcohol-induced conditioned place preference (CPP) behavior and hippocampal neuron plasticity in C57BL/6 mice. Using recombinant adeno-associated viruses to overexpress MMP-9 in the hippocampus, we investigated the NMDAR, PSD-95, and cellular cytoskeleton proteins F-actin/G-actin in the modulation of alcohol reward behavior in mice exposed to CPP. We found that hippocampal infusions of MMP-9 decreased alcohol-induced place preference suggesting a reduction in alcohol reward. Western blot analysis demonstrated that protein expression of NMDA receptors (GluN1, GluN2A and GluN2B) in the hippocampus of alcohol-exposed mice were higher than that of the saline group. Further, the expression of these proteins was decreased in MMP-9 overexpressing mice. MMP-9 also regulated the ratio of F-actin/G-actin (dendritic spines cytoskeleton proteins), which might be the key mediator for behavioral changes in mice. Consequently, our results highlight new evidence that MMP-9 may play an important role in the molecular mechanism underlying alcohol reward and preference.

Downregulation of miR‑29b‑3p promotes α‑tubulin deacetylation by targeting the interaction of matrix metalloproteinase‑9 with integrin β1 in nasal polyps

Matrix metalloproteinase (MMP)‑9 is a key enzyme responsible for extracellular matrix degradation and contributes to the progressive histological changes observed in lower respiratory tract infections. Integrin β1 and α‑tubulin are potential MMP‑9‑interacting proteins, and microRNA (miR)‑29b‑3p can regulate MMP‑9 expression. MMP‑9 is highly expressed in chronic rhinosinusitis with nasal polyps (CRSwNPs), regardless of its effects on miR‑29b‑3p, integrin β1 and α‑tubulin expression. In the present study, samples from 100 patients with CRSwNPs were examined via reverse transcription‑quantitative PCR to assess the mRNA expression of miR‑29b‑3p, and western blotting was performed to assess the protein expression of MMP‑2, MMP‑9, acetyl‑α‑tubulin, integrin β1 and tissue inhibitor of metalloproteinase 1 (TIMP‑1). A dual‑luciferase reporter assay was used to verify the direct binding of miR‑29b‑3p and MMP‑2/MMP‑9. Co‑immunoprecipitation (Co‑IP) and GST pull‑down assays showed that integrin β1 and α‑tubulin were MMP‑9‑interacting proteins. Cell viability, apoptosis and inflammatory cytokine levels were determined via a Cell Counting Kit‑8 assay, flow cytometry and ELISA, respectively. miR‑29b‑3p expression was found to be positively correlated with MMP‑2 and MMP‑9 expression. Whereas, TIMP‑1 expression was negatively correlated with MMP‑2 and MMP‑9 expression. The dual‑luciferase assay revealed that miR‑29b‑3p targeted the 3' untranslated region of MMP‑2/MMP‑9. The Co‑IP and GST pull‑down assays showed that MMP‑9 could directly bind to integrin β1 and indirectly bind to α‑tubulin. Finally, the overexpression of miR‑29b‑3p decreased the expression of MMP‑9 and increased the levels of acetyl‑α‑tubulin. By contrast, the knockdown of miR‑29b‑3p increased the expression of MMP‑9 and decreased the levels of acetyl‑α‑tubulin. Additionally, MMP‑9 expression was found to be negatively correlated with acetyl‑α‑tubulin expression. Of note, the expression of integrin β1 did not change following the overexpression and knockdown of MMP‑9. Finally, the overexpression of miR‑29b‑3p not only decreased MMP‑9 expression, but also alleviated lipopolysaccharide‑induced inflammation in NP69 cells. The results showed that the downregulation of miR‑29b‑3p promoted α‑tubulin deacetylation by increasing the number of MMP‑9‑integrin β1 complexes in CRSwNPs, thus targeting miR‑29b‑3p/MMP‑9 may be a potential novel strategy for the clinical treatment of CRSwNPs.

Matrix Metalloproteinase-9 Overexpression Regulates Hippocampal Synaptic Plasticity and Decreases Alcohol Consumption and Preference in Mice

Brain matrix metalloproteinases (MMPs) have been recently implicated in alcohol addiction; however, the molecular mechanisms remain poorly understood. Matrix metalloproteinase-9 (MMP-9), an extrasynaptic protease, is the best described MMP that is thought to regulate addictive behavior. In the present study, the effect of MMP-9 overexpression on hippocampal neuron plasticity and alcoholic behavior was assessed in spontaneous alcohol drinking mice. Two-bottle choice model showed that the overexpression of MMP-9 in the hippocampus developed by adeno-associated virus (AAV) could decrease alcohol consumption and preference, but did not affect taste preference, which was tested using saccharin or quinine solutions. Dendritic spines number of hippocampal neurons was observed by Golgi staining. Compared with the alcohol treatment group, the density of dendritic spines in the hippocampus of alcohol drinking mice was decreased in alcohol + MMP-9 group. Western blot analysis indicated that GluN1 expression in the hippocampus of alcohol drinking group was lower than that in the control group, while the expression of GluN1 was increased in MMP-9 overexpressing mice. MMP-9 also regulated the depolymerization of actin filaments, which induced behavioral changes in mice. Taken together, overexpression of MMP-9 in the hippocampal neurons of mice resulted in decreased dendritic spine density and F-actin/G-actin ratio, which might be the crucial reason for the significant decrease in alcohol consumption in alcohol drinking mice. MMP-9 might be considered as a novel target studying the molecular mechanism of alcohol drinking.

Chronic Intermittent Ethanol Exposure Induces Upregulation of Matrix Metalloproteinase-9 in the Rat Medial Prefrontal Cortex and Hippocampus

Matrix metalloproteinase-9 (MMP-9, Gelatinase B), an extracellular-acting Zn²⁺-dependent endopeptidase, are involved in brain pathologies including ischemia, glioma, and epilepsy. Recent studies suggested that MMP-9 plays an important role in neuronal plasticity, specifically in learning and memory. To determine whether and how MMP-9 plays role in alcohol-related behaviors, male Sprague-Dawley (SD) rats were subjected to chronic intermittent ethanol (CIE) exposure for 4 weeks, following which we collected tissue samples from the hippocampus, medial prefrontal cortex (mPFC), and amygdala at different stages (acute and chronic exposure) during alcohol exposure. Real-time PCR and western blot assays were used to detect changes in the mRNA and protein expression of MMP-9. Our results indicated that both acute and chronic alcohol exposure induced up-regulation of MMP-9 mRNA levels in the hippocampus and mPFC, but not in the amygdala. Furthermore, acute and chronic alcohol exposure up regulated the expression of total MMP-9 and active MMP-9 in these two brain regions. Moreover, the increase of active MMP-9 expression was larger than those in total MMP-9 expression. Immunoprecipitation analyses identified potential MMP-9-interacting proteins, including Itgb1, Src, Eef1a2, tubulin, actin, and histone H2B. These results demonstrate that both acute and CIE exposure induced increases in MMP-9 expression in the mPFC and hippocampus, suggesting that MMP-9 plays a key role in chronic alcohol exposure and dependence.

Molecular Neuropathology of Astrocytes and Oligodendrocytes in Alcohol Use Disorders

Postmortem studies reveal structural and molecular alterations of astrocytes and oligodendrocytes in both the gray and white matter (GM and WM) of the prefrontal cortex (PFC) in human subjects with chronic alcohol abuse or dependence. These glial cellular changes appear to parallel and may largely explain structural and functional alterations detected using neuroimaging techniques in subjects with alcohol use disorders (AUDs). Moreover, due to the crucial roles of astrocytes and oligodendrocytes in neurotransmission and signal conduction, these cells are very likely major players in the molecular mechanisms underpinning alcoholism-related connectivity disturbances between the PFC and relevant interconnecting brain regions. The glia-mediated etiology of alcohol-related brain damage is likely multifactorial since metabolic, hormonal, hepatic and hemodynamic factors as well as direct actions of ethanol or its metabolites have the potential to disrupt distinct aspects of glial neurobiology. Studies in animal models of alcoholism and postmortem human brains have identified astrocyte markers altered in response to significant exposures to ethanol or during alcohol withdrawal, such as gap-junction proteins, glutamate transporters or enzymes related to glutamate and gamma-aminobutyric acid (GABA) metabolism. Changes in these proteins and their regulatory pathways would not only cause GM neuronal dysfunction, but also disturbances in the ability of WM axons to convey impulses. In addition, alcoholism alters the expression of astrocyte and myelin proteins and of oligodendrocyte transcription factors important for the maintenance and plasticity of myelin sheaths in WM and GM. These changes are concomitant with epigenetic DNA and histone modifications as well as alterations in regulatory microRNAs (miRNAs) that likely cause profound disturbances of gene expression and protein translation. Knowledge is also available about interactions between astrocytes and oligodendrocytes not only at the Nodes of Ranvier (NR), but also in gap junction-based astrocyte-oligodendrocyte contacts and other forms of cell-to-cell communication now understood to be critical for the maintenance and formation of myelin. Close interactions between astrocytes and oligodendrocytes also suggest that therapies for alcoholism based on a specific glial cell type pathology will require a better understanding of molecular interactions between different cell types, as well as considering the possibility of using combined molecular approaches for more effective therapies.