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Effect of dietary amino acids on glycerol absorption via intestinal aquaporins: a mechanism for fat accumulation?
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Resumo(s)
As aquaporinas (AQPs) são proteínas transmembranares que em mamíferos constituem uma família de 13 membros (AQP0-12). Atuam como canais bidirecionais seletivos para a água, sendo que em alguns casos transportam também glicerol através das membranas celulares (aquagliceroporinas AQP3, AQP7, AQP9, AQP10). A regulação do transporte do glicerol no trato gastrointestinal é crucial para controlar a deposição de gordura, a lipólise e a gluconeogénese, em que as AQPs podem atuar como mediadores do fornecimento de glicerol, subjacente à função da barreira intestinal. Assim, a investigação do papel das AQPs no intestino delgado pode constituir uma nova abordagem no controlo de doenças metabólicas, tais como obesidade, resistência à insulina ou diabetes. Tendo por base a premissa de que o aminoácido glutamina é um regulador fisiológico da gluconeogénese e que a cistina promove a adiposidade, testámos o perfil transcricional e a funcionalidade das AQPs na porção do íleo do intestino delgado de leitões cujas dietas foram enriquecidas nestes aminoácidos. 20 leitões machos com um peso corporal inicial de 8,8 ± 0,89 kg foram distribuídos aleatoriamente por 4 tratamentos (n = 5) e receberam durante um período de 4 semanas uma dieta basal sem suplemento (dieta controlo) ou suplementada com 8 kg/tonelada de glutamina (Gln), cistina (Cys)2 ou a combinação dos dois em proporções iguais [Gln + (Cys)2]. A maioria dos parâmetros bioquímicos apresentou um aumento ligeiro nos leitões alimentados com a combinação dos aminoácidos. Em termos de perfil transcripcional, os níveis de mRNA da AQP3 foram predominantes quando comparados aos demais (AQP3a > AQP1b > AQP7c > AQP10c > AQP9c). Ambos os aminoácidos, individualmente ou combinados, foram responsáveis por uma desregulação consistente da AQP1, AQP7 e AQP10 sem impacto no coeficiente de permeabilidade à água (Pf) e ao glicerol (Pgly), respetivamente. A expressão do gene da AQP9 apresentou a mesma tendência, embora sem significância estatística. Inversamente, a dieta enriquecida com (Cys)2 aumentou os níveis do gene AQP3 e diminuiu os níveis do gene glicerol quinase (GK), o que não se refletiu na Pgly. Em resumo, as dietas enriquecidas com glutamina ou cistina promovem a desregulação da expressão dos genes das AQPs no intestino delgado dos leitões, apesar de não ter sido detetável o impacto na permeabilidade global da membrana, provavelmente devido a mecanismos compensatórios entre as várias isoformas de AQPs que asseguram a manutenção da homeostase da permeação celular.
Aquaporins (AQPs) are transmembrane proteins grouped in a family of 13 members (AQP0-12) in mammals, acting as bidirectional water-selective channels, and in some cases also transporting glycerol across cell membranes (aquaglyceroporins AQP3, AQP7, AQP9, AQP10). The regulation of glycerol transport in the gastrointestinal tract is crucial to control fat deposition, lipolysis and gluconeogenesis, where AQPs serve as mediators of glycerol delivery, underlying intestinal barrier function. Thus, targeting aquaporins in the small intestine might constitute a novel approach to control metabolic disorders, such as obesity, insulin resistance or diabetes. Based on the premise that glutamine is a physiological regulator of gluconeogenesis whereas cystine promotes adiposity, herein we tested both the transcriptional profile as well as functionality of AQP in the ileum portion of the small intestine of piglets fed on amino acids enriched diets. 20 male piglets with an initial body weight of 8.8 ± 0.89 kg were randomly allocated to 4 dietary treatments with five animals each and received during a 4 week-period a basal diet without supplementation (control) or supplemented with 8 kg/ton of glutamine (Gln), cystine (Cys)2 or the combination of the two amino acids in equal proportions [Gln + (Cys)2]. The majority of biochemical parameters were found improved in piglets fed Gln + (Cys)2 diet. mRNA levels of AQP3 were found predominant over the others (AQP3a > AQP1b > AQP7c > AQP10c > AQP9c). Both amino acids, individually or combined, were responsible for a consistent downregulation of AQP1, AQP7 and AQP10 gene expression without impacting on water (Pf) and glycerol permeability (Pgly) coefficient, respectively. The same trend was verified for AQP9 gene expression, although there is no statistical meaning. Conversely, (Cys)2 enriched diet upregulated AQP3 and downregulated glycerol kinase enzyme (GK), not translated, on Pgly variations. Our results evidence a downregulation of AQPs gene expression promoted by glutamine or cystine enriched diets in the small intestine of piglets. although no impact on overall membrane permeability was detected, probably due to compensatory mechanisms among AQP isoforms aiming to assure the maintenance of cellular permeation homeostasis.
Aquaporins (AQPs) are transmembrane proteins grouped in a family of 13 members (AQP0-12) in mammals, acting as bidirectional water-selective channels, and in some cases also transporting glycerol across cell membranes (aquaglyceroporins AQP3, AQP7, AQP9, AQP10). The regulation of glycerol transport in the gastrointestinal tract is crucial to control fat deposition, lipolysis and gluconeogenesis, where AQPs serve as mediators of glycerol delivery, underlying intestinal barrier function. Thus, targeting aquaporins in the small intestine might constitute a novel approach to control metabolic disorders, such as obesity, insulin resistance or diabetes. Based on the premise that glutamine is a physiological regulator of gluconeogenesis whereas cystine promotes adiposity, herein we tested both the transcriptional profile as well as functionality of AQP in the ileum portion of the small intestine of piglets fed on amino acids enriched diets. 20 male piglets with an initial body weight of 8.8 ± 0.89 kg were randomly allocated to 4 dietary treatments with five animals each and received during a 4 week-period a basal diet without supplementation (control) or supplemented with 8 kg/ton of glutamine (Gln), cystine (Cys)2 or the combination of the two amino acids in equal proportions [Gln + (Cys)2]. The majority of biochemical parameters were found improved in piglets fed Gln + (Cys)2 diet. mRNA levels of AQP3 were found predominant over the others (AQP3a > AQP1b > AQP7c > AQP10c > AQP9c). Both amino acids, individually or combined, were responsible for a consistent downregulation of AQP1, AQP7 and AQP10 gene expression without impacting on water (Pf) and glycerol permeability (Pgly) coefficient, respectively. The same trend was verified for AQP9 gene expression, although there is no statistical meaning. Conversely, (Cys)2 enriched diet upregulated AQP3 and downregulated glycerol kinase enzyme (GK), not translated, on Pgly variations. Our results evidence a downregulation of AQPs gene expression promoted by glutamine or cystine enriched diets in the small intestine of piglets. although no impact on overall membrane permeability was detected, probably due to compensatory mechanisms among AQP isoforms aiming to assure the maintenance of cellular permeation homeostasis.
Descrição
Tese de mestrado, Ciências Biofarmacêuticas, 2020, Universidade de Lisboa, Faculdade de Farmácia
Palavras-chave
Aquaporins Glutamine and cystine Water and glycerol permeability Small intestine Piglets Teses de mestrado - 2020