Biomedical subjects

M Vemula

Publications and source records attributed to M Vemula.

3 recordsLinked to original sources

PubMed2004

Expression profiling analysis of the metabolic and inflammatory changes following burn injury in rats.

Burn injury initiates an inflammatory response as part of the healing process that is associated with extensive metabolic adjustments. While most studies have focused on understanding these changes from a biochemical perspective, not much work has been done to characterize these processes at the gene expression level. As a first step, we have comprehensively analyzed changes in gene expression in rat livers during the first 24 h after burn injury using Affymetrix GeneChips, which showed 339 genes to be differentially expressed at a statistical significance of P < 0.05 and changed at least twofold. Functional classification based on gene ontology terms indicated that two categories, metabolism (28%) and inflammation (14%), accounted for nearly 42%. Detailed analysis of the metabolism group of genes indicated that fatty acid (FA) and triglyceride (TG) biosynthesis in the liver were unchanged, whereas TG utilization, FA import, and beta-oxidation increased after burn injury. The increased FA pools after burn injury appear to serve as substrates for ATP production. Following burn injury, the cholesterol biosynthetic pathway was suppressed while cholesterol was increasingly imported and converted into bile acids. The inflammatory genes that were altered included several classic acute phase response markers, as well as genes involved in the complement, kinin, clotting, and fibrinolytic protein systems. These temporally coordinated changes in gene expression were also corroborated by biochemical measurements for FA, TG, cholesterol, and ATP. Together, these data indicate that FA are increasingly imported and oxidized in the liver to meet the enhanced energy demands arising from an inflammatory response during the first 24 h after burn injury.

Adenosine Triphosphate↗

PubMed2002

Yeast desaturases.

The Saccharomyces OLE1 gene encodes the intrinsic membrane-bound Delta-9 fatty acid desaturase. OLE1 expression is regulated at the levels of transcription and mRNA stability by nutrient fatty acids and molecular oxygen. Its transcription is controlled through two distinct promoter elements, the fatty acid response element (FAR) region, and a downstream low-oxygen response element (LORE) that dramatically amplifies FAR-activated expression under hypoxic or cobalt-stimulated growth conditions. Transcription activation through both elements is repressed by unsaturated fatty acids. The half-life of the OLE1 mRNA is also dramatically reduced upon exposure to unsaturated fatty acids. OLE1 expression is governed by two homologous membrane-bound proteins, Spt23p and Mga2p, which activate OLE1 expression through N-terminal polypeptides that are released from the membrane through a ubiquitin-mediated mechanism that involves processing by the 23 S proteosome. Although proteolytic processing of Spt23p can be repressed by polyunsaturated fatty acids, Mga2p processing in normoxic cells appears to be regulated by a different mechanism. Mga2p is essential, however, for the induction of the high levels of expression that are triggered by hypoxia through the LORE promoter element. Surprisingly, Mga2p also plays a critical role in controlling OLE1 mRNA stability, suggesting that there may be a functional linkage between OLE1 transcription and the regulation of OLE1 mRNA stability.

Fatty Acid Desaturases↗

PubMed2001

The membrane proteins, Spt23p and Mga2p, play distinct roles in the activation of Saccharomyces cerevisiae OLE1 gene expression. Fatty acid-mediated regulation of Mga2p activity is independent of its proteolytic processing into a soluble transcription activator.

The Saccharomyces OLE1 gene encodes the Delta-9 fatty acid desaturase, an enzyme that converts saturated fatty acyl-CoAs into cis-Delta-9 unsaturated fatty acids. OLE1 gene expression is regulated by unsaturated fatty acids, which repress transcription and destabilize the OLE1 mRNA. Expression of OLE1 is activated by N-terminal proteolytic fragments of two homologous endoplasmic reticulum membrane proteins, Spt23p and Mga2p. Disruption of either gene does not significantly affect cell growth or fatty acid metabolism; cells that contain null alleles of both genes, however, are unsaturated fatty acid auxotrophs. An analysis of spt23Delta and mga2Delta strains shows that Spt23p and Mga2p differentially activate and regulate OLE1 transcription. In glucose-grown cells, both genes activate transcription to similar levels of activity. Expressed alone, Mga2p induces high levels of OLE1 transcription in cells exposed to cobalt or grown in glycerol-containing medium. Spt23p expressed alone activates OLE1 transcription to levels similar to those in wild type cells. OLE1 expression is strongly repressed by unsaturated fatty acids in spt23Delta or mga2Delta cells, under all growth conditions. To test if OLE1 expression is controlled by fatty acids at the level of membrane proteolysis, soluble N-terminal fragments of Spt23p and Mga2p that lack their membrane-spanning regions (Deltatm) were expressed under the control of their native promoters in spt23Delta;mga2Delta cells. Under those conditions, Mga2pDeltatm acts as a powerful transcription activator that is strongly repressed by unsaturated fatty acids. By comparison, the Spt23pDeltatm polypeptide weakly activates transcription and shows little regulation by unsaturated fatty acids. Co-expression of the two soluble fragments results in activation to levels observed with the Mga2pDeltatm protein alone. The fatty acid repression of transcription under those conditions is attenuated by Spt23Deltatm, however, suggesting that the two proteins may interact to modulate OLE1 gene expression.

Base Sequence↗