Olive Leaf Polyphenols (OLPs) Stimulate GLUT4 Expression and Translocation in the Skeletal Muscle of Diabetic Rats

Skeletal muscles are high-insulin tissues responsible for disposing of glucose via the highly regulated process of facilitated glucose transporter 4 (GLUT4). Impaired insulin action in diabetes, as well as disorders of GLUT4 vesicle trafficking in the muscle, are involved in defects in insulin-stimulated GLUT4 translocation. Since the Rab GTPases are the main regulators of vesicular membrane transport in exo- and endo-cytosis, in the present work, we studied the effect of olive leaf polyphenols (OLPs) on Rab8A, Rab13, and Rab14 proteins of the rat soleus muscle in a model of streptozotocin (SZT)-induced diabetes (DM) in a dose-dependent manner. Glucose, cholesterol, and triglyceride levels were determined in the blood, morphological changes of the muscle tissue were captured by hematoxylin and eosin histological staining, and expression of GLUT4, Rab8A, Rab13, and Rab14 proteins were analyzed in the rat soleus muscle by the immunofluorescence staining and immunoblotting. OLPs significantly reduced blood glucose level in all treated groups. Furthermore, significantly reduced blood triglycerides were found in the groups with the lowest and highest OLPs treatment. The dynamics of activation of Rab8A, Rab13, and Rab14 was OLPs dose-dependent and more effective at higher OLP doses. Thus, these results indicate a beneficial role of phenolic compounds from the olive leaf in the regulation of glucose homeostasis in the skeletal muscle.

Endoplasmic reticulum resident heat shock protein-gp96 as morphogenetic and immunoregulatory factor in syngeneic pregnancy

The severe remodeling of endometrial stroma during blastocyst adhesion and trophoblast invasion initiates at maternal-fetal interface the reaction of evolutionary old heat shock response, in which heat shock proteins, as molecular chaperons, monitor the configurations of newly synthesized proteins and prevent the formation of functionless aggregates of misfolded proteins, targeting them to degradation by a the ubiquitin-proteasome system. In addition, the endoplasmic reticulum (ER)-resident HSPs, such as gp96/GRP94 may, after binding to CD91 and TLRs, elicit antigen-specific and antigen-unspecific immune responses, owing to its peptide-chaperoning capacity and ability to activate APCs. Considering these properties, we examined tissue expression of gp96 at the maternal-fetal interface and in the maternal liver and spleen on the 16th day of undisturbed syngeneic pregnancy and after the treatment with peptidoglycan monomer linked with zinc (PGM-Zn). The data showed that in undisturbed pregnancy the gp96, CD91 and TLR2 were markedly expressed on extravillous and villous trophoblast. PGM-Zn enhanced these findings, as well as the number of uterine natural killer cells and local NFκB immunoreactivity. Gp96 expression arose also in the maternal spleen and liver, where an accumulation of NKT cells or γδT lymphocytes was seen. The data point to roles of gp96 in maintenance of proteostasis and local and systemic immune balance in pregnancy complicated by infection.

Metallothioneins I/II expression in rat strains with genetically different susceptibility to experimental autoimmune encephalomyelitis

OBJECTIVES

Compared to the Dark Agouti (DA), the Albino Oxford (AO) rat strain exhibits lower susceptibility to the induction of experimental autoimmune encephalomyelitis (EAE). Here, we investigated the potential contribution of the heavy metal-binding proteins metallothioneins (MTs) I/II to these effects.

METHODS

Rats were immunized with bovine brain homogenate emulsified in complete Freund's adjuvant or only with complete Freund's adjuvant. The expression patterns of MTs mRNA and proteins and tissue concentrations of Zn2+ and Cu2+ were estimated in the brain and in the liver on days 7 and 12 after immunization, by real-time PCR, immunohistochemistry and inductively coupled plasma spectrometry, respectively. Additionally, the hepatic transforming growth factor beta and nuclear factor kappa B immunoreactivities were tested.

RESULTS

Clinical signs of EAE were not induced in AO rats, but they upregulated the expression of MT I/II proteins in the brain (hippocampus and cerebellum) and in the liver, similarly as DA rats. The transcriptional activation of MT-I occurred, however, only in DA rats, which accumulated also more zinc in the brain and in the liver. In contrast, intact AO rats had greater hepatic MT-I mRNA immunoreactivity and more Cu2+ in the hippocampus. Besides, in immunized AO rats a high upregulation of transforming growth factor beta and nuclear factor kappa B immunoreactivities was found in several hepatic structures (vascular endothelium, Kupffer cells and hepatocytes).

CONCLUSIONS

Our data show that AO and DA rats differ in constitutive and inductive MT-I gene expression in the brain and in the liver, as well as in the hepatic cytokine profile, suggesting that these mechanisms may contribute to the discrepancy in the susceptibility to EAE.