José Manuel Horcas Nieto

209 7 General Discussion and 90s of the twentieth century and lack information on oxidation of verylong-chain fatty acids or branched-chain fatty acids39. This was due to the insoluble nature of these compounds making it challenging to work with them. Moreover, very little information on kinetic parameters of the transporters is available. In order to perform kinetic studies, transporters are often reconstituted in liposomes to perform transport assays which can be affected by lipid membrane dynamics40. As a solution, I propose to re-visit the early kinetic studies making use of the current technology to fully characterize the mechanism and kinetic parameters of the enzymes of interest, making for new and more detailed kinetic models. PART 2. THE IMPORTANCE OF PEROXISOMES AND MITOCHONDRIAL IN FATTY ACID METABOLISM AND THEIR INTERPLAY IN HEALTH AND DISEASE The main aim of the thesis was to develop in vitro and in silico models to study two diseases affecting fatty acid metabolism. In both diseases, peroxisomes and mitochondria are involved, highlighting the importance and interplay of these two metabolic organelles. While mitochondria have been extensively studied and characterized, we have an incomplete overview of the many peroxisomal functions that are still being discovered. Recent studies have described peroxisomes to be involved in different processes such as aging41, immunometabolism42, etc. Peroxisomes and mitochondria in Severe Malnutrition In chapter 2, I focused on the effects of malnutrition on peroxisomes and mitochondria both in the liver and the intestine and the mechanisms regulating the balance between biosynthesis and degradation of both organelles. As a proxy to malnutrition, I exposed the organoids to amino-acid restricted media for different periods of time. The amino-acid restricted conditions in our studies mimic the effects of low protein diets, leading to a reduction in peroxisomal and mitochondrial mass and function. In the case of the liver, mitochondrial loss is described to follow peroxisomal degradation while this time dependence was not observed in the intestinal organoids. However, while the loss of peroxisomes and mitochondria in the hepatic organoids recapitulates the findings of the in vivo models14, the loss of peroxisomes observed in the malnourished intestinal organoids has not yet been investigated in vivo. In chapter 4, I discussed whether the reduction in peroxisomal number in the

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