Involvement of PKC and PKA in the inhibitory effect of leptin on intestinal galactose absorption

Studies from our laboratory have demonstrated that leptin inhibits galactose absorption in vitro by acting on the Na(+)/glucose cotransporter SGLT1. Since PKC and PKA are involved in the regulation of SGLT1 and leptin is able to activate these kinases, we have investigated the possible implication of PKC and PKA in the inhibition of sugar absorption by leptin in rat small intestinal rings. Inhibition of 1 mM galactose uptake by 0.2 nM leptin is blocked by 2 microM chelerythrine, a PKC inhibitor, which by itself does not affect galactose uptake. However, 1 microM H-89, a PKA inhibitor, inhibits galactose uptake and does not block leptin inhibition. Biochemical assays show that the inhibitory effect of leptin is accompanied by a approximately 2-fold increase in PKA and PKC activity. These findings indicate that the activation of PKC is more relevant than PKA activation in the inhibition of galactose absorption by leptin.     

Structure and conformational stability of the enzyme I of Streptomyces coelicolor explored by FTIR and circular dichroism

The bacterial phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS), formed by a cascade of several proteins, couples the translocation and phosphorylation of specific sugars across cell membranes. The structure and thermal stability of the first protein (enzyme I, EI) of the PTS in Streptomyces coelicolor is studied by using far-UV circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) at pH 7.0. The deconvolution of FTIR spectra indicates that the protein is mainly composed by a 35% of alpha-helical structure and 30% of beta-sheet. The thermal denaturation curves, as followed by both techniques, show only a midpoint at 330 K. This thermal denaturation behaviour is different to that observed in other members of the EI family.     

The cellular prion protein and its role in Alzheimer disease

The cellular prion protein (PrP^C) is a membrane-bound glycoprotein especially abundant in the central nervous system (CNS). The scrapie prion protein (PrP^Sc, also termed prions) is responsible of transmissible spongiform encephalopathies (TSE), a group of neurodegenerative diseases which affect humans and other mammal species, although the presence of PrP^C is needed for the establishment and further evolution of prions.The present work compares the expression and localization of PrP^C between healthy human brains and those suffering from Alzheimer disease (AD).In both situations we have observed a rostrocaudal decrease in the amount of PrP^C within the CNS, both by immunoblotting and immunohistochemistry techniques. PrP^C is higher expressed in our control brains than in AD cases. There was a neuronal loss and astogliosis in our AD cases. There was a tendency of a lesser expression of PrP^C in AD cases than in healthy ones. And in AD cases, the intensity of the expression of the unglycosylated band is higher than the di- and monoglycosylated bands.With regards to amyloid plaques, those present in AD cases were positively labeled for PrP^C, a result which is further supported by the presence of PrP^C in the amyloid plaques of a transgenic line of mice mimicking AD.The work was done according to Helsinki Declaration of 1975, and approved by the Ethics Committee of the Faculty of Medicine of the University of Navarre.Key words: cellular prion protein, Alzheimer disease, transgenic mice