👤 Heike Pospisil

Changes in fatty acid metabolism associated with insulin resistance have been described in rats and humans but have not been well characterized in the frequently used mouse model of diet-induced obesity. To analyse the early phase as well as established insulin resistance, C57BL/6 mice were placed for 1 or 16 weeks on a high fat diet (1w-HFD, 16w-HFD). Endocrine and metabolic parameters indicated that 1w-HFD mice showed a moderate but significant induction of insulin resistance while 16w-HFD mice exhibited profound obesity-associated insulin resistance and dyslipidemias. Significant alterations in fatty acid composition were observed in plasma and liver in both groups. Liver phospholipid-associated arachidonate and docosahexaenoate were increased in both 1w-HFD and 16w-HFD mice, possibly due to increased expression of the desaturases Fads1 and Fads2. Unexpectedly, SCD1 activity and gene expression in liver were decreased in the 1w-HFD group accompanied by diminished total hepatic lipid levels, while they were increased in chronically fed mice. Our data indicate that the early phase of HFD-induced insulin resistance is not associated with elevated liver lipid concentration. Furthermore, the early and persistent rise of arachidonate and docosahexaenoate indicates that insulin resistance is not due to insufficient availability (or concentrations) of polyunsaturated fatty acids as postulated previously. Show less

Splicing processes might play a major role in carcinogenesis and tumour progression. The Wnt pathway is of crucial relevance for cancer progression. Therefore we focussed on the Wnt/beta-catenin signalling pathway in order to validate the expression of sequences predicted as alternatively spliced by bioinformatic methods. Splice variants of its key molecules were selected, which may be critical components for the understanding of colorectal tumour progression and may have the potential to act as biological markers. For some of the Wnt pathway genes the existence of splice variants was either proposed (e.g. beta-Catenin and CTNNB1) or described only in non-colon tissues (e.g. GSK3beta) or hitherto not published (e.g. LRP5). Both splice variants--normal and alternative form--of all selected Wnt pathway components were found to be expressed in cell lines as well as in samples derived from tumour, normal and healthy tissues. All splice positions corresponded totally with the bioinformatical prediction as shown by sequencing. Two hitherto not described alternative splice forms (CTNNB1 and LRP5) were detected. Although the underlying EST data used for the bioinformatic analysis suggested a tumour-specific expression neither a qualitative nor a significant quantitative difference between the expression in tumour and healthy tissues was detected. Axin-1 expression was reduced in later stages and in samples from carcinomas forming distant metastases. We were first to describe that splice forms of crucial genes of the Wnt-pathway are expressed in human colorectal tissue. Newly described splicefoms were found for beta-Catenin, LRP5, GSK3beta, Axin-1 and CtBP1. However, the predicted cancer specificity suggested by the origin of the underlying ESTs was neither qualitatively nor significant quantitatively confirmed. That let us to conclude that EST sequence data can give adequate hints for the existence of alternative splicing in tumour tissues. That no difference in the expression of these splice forms between cancerous tissues and normal mucosa was found, may indicate that the existence of different splice forms is of less significance for cancer formation as suggested by the available EST data. The currently available EST source is still insufficient to clearly deduce colon cancer specificity. More EST data from colon (tumour and healthy) is required to make reliable predictions. Show less