Search

Fabry disease is an X-linked sphingolipid storage disorder caused by a deficiency of the lysosomal enzyme α-galactosidase A (AGA, EC 3.2.1.22) resulting in the intracellular accumulation of globotriaosylceramide (Gb3). We found that Gb3 storage also correlates with accumulation of endosomal-lysosomal cholesterol in Fabry fibroblasts. This cholesterol accumulation may contribute to the phenotypic pathology of Fabry disease by slowing endosomal-lysosomal trafficking. We found that LDL receptor expression is not downregulated in Fabry fibroblasts resulting in accumulation of both cholesterol and Gb3. 5A-Palmitoyl oleoyl-phosphatidylcholine (5AP) is a phospholipid complex containing a short synthetic peptide that mimics apolipoprotein A1, the main protein component of high-density lipoprotein (HDL) that mediates the efflux of cholesterol from cells via the ATP-binding cassette transporter. We used 5AP and HDL to remove cholesterol from Fabry fibroblasts to examine the fate of accumulated cellular Gb3. Using immunostaining techniques, we found that 5AP is highly effective for depleting cholesterol and Gb3 in these cells. 5AP restores the ApoA-1-mediated cholesterol efflux leading to mobilization of cholesterol and reduction of Gb3 in Fabry fibroblasts.

Leptin acts not only as an anorexigenic hormone but also regulates cell-mediated immunity via leptin receptors (Ob-R) expressed on T and B lymphocytes. However, the impact of leptin on natural killer (NK) cells is currently elusive. We evaluated leptin effects on NK cells in relation to the body weight in rats using in vivo and in vitro approaches. Leptin was injected iv in male lean and diet-induced obese Lewis and F344 rats. NK cell numbers were analyzed in blood and spleen by fluorescence activated cell sorting and immunohistochemistry, and the activity of NK cells was measured by chromium release assay. Ob-R expression was investigated by confocal laser scanning and quantitative RT-PCR. To compare leptin-dependent intracellular signaling under basal and leptin- and tumor cell (MADB106)-stimulated conditions, intracellular target proteins of NK cells were evaluated by Western blotting. Number and distribution pattern of splenic NK cells were significantly different in lean and obese animals. Leptin administration resulted in a 4-fold higher stimulation of the NK activity in lean than obese animals. This was not due to a decreased expression of Ob-R because quantitative RT-PCR revealed significantly higher Ob-Rb mRNA levels in NK cells from obese rats. In contrast, postreceptor signaling is differentially abrogated in obese animals with significantly lower activation of postreceptor signaling components (Janus kinase-2p, protein kinase B pT308, AMPalphapT172) after an in vivo leptin challenge. In conclusion, the results for the first time assign leptin a central role as a modulator of NK cell number and activity only in lean but not obese subjects. The differential role of leptin has important implications for the influence of body weight in the response to systemic inflammations and in the immunological defense of cancer.