INTRODUCTION Carnitine palmitoyltransferase I, which is expressed in the pancreas as the liver isoform (LCPTI), catalyzes the rate-limiting step in the transport of fatty acids into the mitochondria for their oxidation. To directly examine whether the availability of long-chain fatty acyl-CoA affects the regulation of insulin secretion in the Beta-cell, we infected INS(832/13) cells and rat islets with an adenovirus encoding a mutant form of LCPTI (Ad-LCPTI M593S) that is insensitive to its inhibitor malonyl-CoA. C75 is described as a potential drug for treatment of obesity and type 2 diabetes. First known as a synthetic inhibitor of fatty acid synthase, it has been also described as an activator of CPTI, increasing peripheral energy utilization and fatty acid oxidation in mice. To further investigate the C75/CPTI interaction, we have characterized the effects of C75 on CPTI in vitro and in vivo.OBJECTIVES 1) Study of the malonyl-CoA/CPTI interaction in the pancreatic Beta-cell and its involvement in glucose-stimulated insulin secretion (GSIS). 2) Construction of an INS stable cell line overexpressing LCPTI wt and LCPTI M593S. 3) Determine the effect of C75 on the CPTI activity and palmitate oxidation in pancreatic Beta-cells. RESULTS. In Ad-LCPTI M593S infected INS(832/13) cells LCPTI activity increased six-fold. This was associated with enhanced fatty acid oxidation, at any glucose concentration, and a 60% suppression of GSIS. In isolated rat islets in which LCPTI M593S was overexpressed, GSIS decreased 40%. At high glucose concentration, overexpression of LCPTI M593S reduced partitioning of exogenous palmitate into lipid esterification products, and decreased PKC activation. Moreover, LCPTI M593S expression impaired KATP channel-independent GSIS in INS(832/13) cells. INS-1 stable clones of LCPTIwt and LCPTImut were constructed, however none of them resulted in an increase in LCPTI protein expression compared to endogenous LCPTI nor in CPTI activity. Therefore, slight basal overexpression of LCPTI could probably be toxic for the cells, as a result of which only those cells that do not contain the LCPTI plasmids survived throughout cell passages. When INS(823/13) cells are incubated with C75, CPTI activity is inhibited, as is fatty acid oxidation. In vivo, a single intraperitoneal injection of C75 to mice produces a short-term inhibition of CPTI activity in mitochondria from liver and pancreas.DISCUSSION. The results with LCPTImut provide direct support for the hypothesis proposing that the malonyl-CoA/CPTI interaction is a component of a metabolic signalling network that controls insulin secretion. Overall, the findings with C75 provide compelling evidence that the drug is a potent inhibitor of CPTI.
| Identifer | oai:union.ndltd.org:TDX_UB/oai:www.tdx.cat:10803/2999 |
| Date | 24 November 2004 |
| Creators | Herrero Rodríguez, Laura |
| Contributors | Asins Muñoz, Guillermina, García Hegardt, Fausto, Universitat de Barcelona. Departament de Bioquímica i Biologia Molecular (Divisió IV) |
| Publisher | Universitat de Barcelona |
| Source Sets | Universitat de Barcelona |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Source | TDX (Tesis Doctorals en Xarxa) |
| Rights | info:eu-repo/semantics/openAccess, ADVERTIMENT. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. Tampoc s'autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs. |
Page generated in 0.002 seconds