Search

Thyroid hormone (TH) target cells need to adopt mechanisms to maintain sufficient levels of TH to ensure regular functions. This includes thyroid epithelial cells, which generate TH in addition to being TH-responsive. However, the cellular and molecular pathways underlying thyroid auto-regulation are insufficiently understood. In order to investigate whether thyroglobulin processing and TH export are sensed by thyrocytes, we inactivated thyroglobulin-processing cathepsins and TH-exporting monocarboxylate transporters (Mct) in the mouse. The states of thyroglobulin storage and its protease-mediated processing and degradation were related to the levels of TH transporter molecules by immunoblotting and immunofluorescence microscopy. Thyroid epithelial cells of cathepsin-deficient mice showed increased Mct8 protein levels at the basolateral plasma membrane domains when compared to wild type controls. While the protein amounts of the thyroglobulin-degrading cathepsin D remained largely unaffected by Mct8 or Mct10 single-deficiencies, a significant increase in the amounts of the thyroglobulin-processing cathepsins B and L was detectable in particular in Mct8/Mct10 double deficiency. In addition, it was observed that larger endo-lysosomes containing cathepsins B, D, and L were typical for Mct8- and/or Mct10-deficient mouse thyroid epithelial cells. These data support the notion of a crosstalk between TH transporters and thyroglobulin-processing proteases in thyroid epithelial cells. We conclude that a defect in exporting thyroxine from thyroid follicles feeds back positively on its cathepsin-mediated proteolytic liberation from the precursor thyroglobulin, thereby adding to the development of auto-thyrotoxic states in Mct8 and/or Mct10 deficiencies. The data suggest TH sensing molecules within thyrocytes that contribute to thyroid auto-regulation.

Background: Methamphetamine is a drug of abuse that disrupts the blood-brain barrier. Results: Blocking actin nucleation protects against methamphetamine-induced occludin internalization and disruption of blood-brain barrier integrity. Conclusion: Methamphetamine-induced transendothelial breaches may result from actin-mediated redistribution of occludin. Significance: Actin cytoskeletal dynamics modulates redistribution of occludin and blood-brain barrier integrity., Methamphetamine (METH) is a drug of abuse with neurotoxic and neuroinflammatory effects, which include disruption of the blood-brain barrier (BBB) and alterations of tight junction protein expression. This study focused on the actin cytoskeletal rearrangement as a modulator of METH-induced redistribution of tight junction protein occludin in brain endothelial cells. Exposure to METH resulted in a shift of occludin localization from plasma membranes to endosomes. These changes were accompanied by activation of the actin-related protein 2/3 (Arp2/3) complex, which stimulates actin polymerization by promoting actin nucleation. In addition, METH-induced coronin-1b phosphorylation diminishes the inhibitory effect of nonphosphorylated coronin-1b on actin nucleation. Blocking actin nucleation with CK-666, a specific inhibitor of the Arp2/3 complex, protected against METH-induced occludin internalization and increased transendothelial monocyte migration. Importantly, treatment with CK-666 attenuated a decrease in occludin levels in brain microvessels and BBB permeability of METH-injected mice. These findings indicate that actin cytoskeletal dynamics is detrimental to METH-induced BBB dysfunction by increasing internalization of occludin.