Impact of the gut microbiome on nicotine's motivational effects and glial cells in the ventral tegmental area in male mice.

A link between gut dysbiosis and the pathogenesis of brain disorders has been identified. A role for gut bacteria in drug reward and addiction has been suggested but very few studies have investigated their impact on brain and behavioral responses to addictive drugs so far. In particular, their influence on nicotine's addiction-like processes remains unknown. In addition, evidence shows that glial cells shape the neuronal activity of the mesolimbic system but their regulation, within this system, by the gut microbiome is not established. We demonstrate that a lack of gut microbiota in male mice potentiates the nicotine-induced activation of sub-regions of the mesolimbic system. We further show that gut microbiota depletion enhances the response to nicotine of dopaminergic neurons of the posterior ventral tegmental area (pVTA), and alters nicotine's rewarding and aversive effects in an intra-VTA self-administration procedure. These effects were not associated with gross behavioral alterations and the nicotine withdrawal syndrome was not impacted. We further show that depletion of the gut microbiome modulates the glial cells of the mesolimbic system. Notably, it increases the number of astrocytes selectively in the pVTA, and the expression of postsynaptic density protein 95 in both VTA sub-regions, without altering the density of the astrocytic glutamatergic transporter GLT1. Finally, we identify several sub-populations of microglia in the VTA that differ between its anterior and posterior sub-parts, and show that they are re-organized in conditions of gut microbiota depletion. The present study paves the way for refining our understanding of the pathophysiology of nicotine addiction.

Sushi domain-containing protein 4 controls synaptic plasticity and motor learning.

Fine control of protein stoichiometry at synapses underlies brain function and plasticity. How proteostasis is controlled independently for each type of synaptic protein in a synapse-specific and activity-dependent manner remains unclear. Here, we show that Susd4, a gene coding for a complement-related transmembrane protein, is expressed by many neuronal populations starting at the time of synapse formation. Constitutive loss-of-function of Susd4 in the mouse impairs motor coordination adaptation and learning, prevents long-term depression at cerebellar synapses, and leads to misregulation of activity-dependent AMPA receptor subunit GluA2 degradation. We identified several proteins with known roles in the regulation of AMPA receptor turnover, in particular ubiquitin ligases of the NEDD4 subfamily, as SUSD4 binding partners. Our findings shed light on the potential role of SUSD4 mutations in neurodevelopmental diseases.

Insulin receptor isoform A favors tumor progression in human hepatocellular carcinoma by increasing stem/progenitor cell features.

Hepatocellular carcinoma (HCC) is one of the most common and deadly neoplasms. Insulin receptor (IR) exists in two isoforms, IR-A and IR-B, the latter being predominantly expressed in normal adult hepatocytes while IR-A is overexpressed in HCC to the detriment of IR-B. This study evaluated the biological functions associated with IR-A overexpression in HCC in relation to expression of its ligand IGF-II. The value of INSRA:INSRB ratio which was increased in ˜70% of 85 HCC was associated with stem/progenitor cell features such as cytokeratin-19 and α-fetoprotein and correlated with shorter patient survival. IGF2 mRNA upregulation was observed in 9.4% of HCC and was not associated with higher INSRA:INSRB ratios. Ectopic overexpression of IR-A in two HCC cell lines presenting a strong autocrine IGF-II secretion loop or not stimulated cell migration and invasion. In cells cultured as spheroids, IR-A overexpression promoted gene programs related to stemness, inflammation and cell movement. IR-A also increased cell line tumorigenicity in vivo after injection to immunosuppressed mice and the sphere-forming cells made a significant contribution to this effect. Altogether, these results demonstrate that IR-A is a novel player in HCC progression.

The IGF2/IR/IGF1R Pathway in Tumor Cells and Myofibroblasts Mediates Resistance to EGFR Inhibition in Cholangiocarcinoma.

Purpose: Cholangiocarcinoma (CCA) is a desmoplastic tumor of the biliary tree in which epidermal growth factor receptor (EGFR) is overexpressed and contributes to cancer progression. Although EGFR has been envisaged as a target for therapy, treatment with tyrosine kinase inhibitors (TKI) such as erlotinib did not provide therapeutic benefit in patients with CCA, emphasizing the need to investigate resistance mechanisms against EGFR inhibition.Experimental Design: Resistant CCA cells to EGFR inhibition were obtained upon long-time exposure of cells with erlotinib. Cell signaling, viability, migration, and spheroid growth were determined in vitro, and tumor growth was evaluated in CCA xenograft models.Results: Erlotinib-resistant CCA cells displayed metastasis-associated signatures that correlated with a marked change in cell plasticity associated with an epithelial-mesenchymal transition (EMT) and a cancer stem cell (CSC)-like phenotype. Resistant cells exhibited an upregulation of insulin receptor (IR) and insulin-like growth factor (IGF) 1 receptor (IGF1R), along with an increase in IGF2 expression. IR/IGF1R inhibition reduced EMT and CSC-like traits in resistant cells. In vivo, tumors developed from resistant CCA cells were larger and exhibited a more prominent stromal compartment, enriched in cancer-associated fibroblasts (CAF). Pharmacological coinhibition of EGFR and IR/IGF1R reduced tumor growth and stromal compartment in resistant tumors. Modeling of CCA-CAF crosstalk showed that IGF2 expressed by fibroblasts boosted IR/IGF1R signaling in resistant cells. Furthermore, IR/IGF1R signaling positively regulated fibroblast proliferation and activation.Conclusions: To escape EGFR-TKI treatment, CCA tumor cells develop an adaptive mechanism by undergoing an IR/IGF1R-dependent phenotypic switch, involving a contribution of stromal cells. Clin Cancer Res; 24(17); 4282-96. ©2018 AACR.

Mitogen-activated protein kinase-activated protein kinase 2 mediates resistance to hydrogen peroxide-induced oxidative stress in human hepatobiliary cancer cells.

The development and progression of liver cancer are characterized by increased levels of reactive oxygen species (ROS). ROS-induced oxidative stress impairs cell proliferation and ultimately leads to cell death. Although liver cancer cells are especially resistant to oxidative stress, mechanisms of such resistance remain understudied. We identified the MAPK-activated protein kinase 2 (MK2)/heat shock protein 27 (Hsp27) signaling pathway mediating defenses against oxidative stress. In addition to MK2 and Hsp27 overexpression in primary liver tumors compared to adjacent nontumorous tissues, the MK2/Hsp27 pathway is activated by hydrogen peroxide-induced oxidative stress in hepatobiliary cancer cells. MK2 inactivation or inhibition of MK2 or Hsp27 expression increases caspase-3 and PARP cleavage and DNA breaks and therefore cell death. Interestingly, MK2/Hsp27 inhibition decreases antioxidant defenses such as heme oxygenase 1 through downregulation of the transcription factor nuclear factor erythroid-derived 2-like 2. Moreover, MK2/Hsp27 inhibition decreases both phosphorylation of epidermal growth factor receptor (EGFR) and expression of its ligand, heparin-binding EGF-like growth factor. A new identified partner of MK2, the scaffold PDZ protein EBP50, could facilitate these effects through MK2/Hsp27 pathway regulation. These findings demonstrate that the MK2/Hsp27 pathway actively participates in resistance to oxidative stress and may contribute to liver cancer progression.