Aging exacerbates oxidative stress and liver fibrosis in an animal model of Down Syndrome

Abstract

Down Syndrome (DS) is a common genetic disorder characterized by an extra copy of chromosome 21, leading to dysregulation of various metabolic pathways. Oxidative stress in DS is associated with neurodevelopmental defects, neuronal dysfunction, and a dementia onset resembling Alzheimer's disease. Additionally, chronic oxidative stress contributes to cardiovascular diseases and certain cancers prevalent in DS individuals. This study investigates the impact of ageing on oxidative stress and liver fibrosis using a DS murine model (Ts2Cje mice). Our results show that DS mice show increased liver oxidative stress and impaired antioxidant defenses, as evidenced by reduced glutathione levels and increased lipid peroxidation. Therefore, DS liver exhibits an altered inflammatory response and mitochondrial fitness as we showed by assaying the expression of HMOX1, CLPP, and the heat shock proteins Hsp90 and Hsp60. DS liver also displays dysregulated lipid metabolism, indicated by altered expression of PPARα, PPARγ, FATP5, and CTP2. Consistently, these changes might contribute to non-alcoholic fatty liver disease development, a condition characterized by liver fat accumulation. Consistently, histological analysis of DS liver reveals increased fibrosis and steatosis, as showed by Col1a1 increased expression, indicative of potential progression to liver cirrhosis. Therefore, our findings suggest an increased risk of liver pathologies in DS individuals, particularly when combined with the higher prevalence of obesity and metabolic dysfunctions in DS patients. These results shed a light on the liver's role in DS-associated pathologies and suggest potential therapeutic strategies targeting oxidative stress and lipid metabolism to prevent or mitigate liver-related complications in DS individuals.

Keywords: Down Syndrome; aging; liver; oxidative stress.

Figure 1

DS mice are characterized by an increased oxidative stress. (A) GSH levels are decreased in Ts2Cje 12-months old mice liver. Representative scheme for GSH quantitation in Eu and Ts2Cje livers obtained from 3-, 6-, 9-, and 12-months old mice. (B) LOOH levels are increased in Ts2Cje 12-months old mice liver. Histograms representative of LOOH spectrophotometric evaluation on Eu and TS2Cje livers obtained from 3-, 6-, 9-, and 12-months old mice. (C) HMOX1 expression is downregulated in Ts2Cje 12-months old livers. Representative histogram of the real-time PCR against HMOX1 on the liver extract obtained from 3-, 6-, 9-, and 12-months old Eu and Ts2Cje mice. GAPDH was used as housekeeping gene. Histograms are representative of four different experiments (^*P ≤ 0.05; ^***P ≤ 0.001).

Figure 2

DS mice show a marked increase in liver inflammation. Western blot analysis on 12-months old Eu and Ts2Cje liver extracts against Hsp90, Hsp60, and Clpp (A). Ts2Cje mice showed a decreased Hsp90 (B), Hsp60 (C) levels, while Clpp accumulation is increased (D). GAPDH was used as housekeeping protein. Histograms are representative of four different experiments (^*P ≤ 0.05; ^**P ≤ 0.01).

Figure 3

DS mice have a marked increase in lipid metabolism. PPARα, PPARγ, FATP5, and CTP2 are differently regulated in Ts2Cje livers. Representative histogram of the real-time PCR against PPARa (A), PPARg (B), FATP5 (C), and CTP2 (D) on the liver extract obtained from 12-months old Eu and Ts2Cje mice. GAPDH was used as housekeeping gene. Histograms are representative of four different experiments (^*P ≤ 0.05).

Figure 4

DS mice show a marked increase in fibrotic markers. (A) Col1a1 expression level is increased in Ts2Cje livers. Representative histogram of the real-time PCR against Col1a1 on the liver extract obtained from 12-months old Eu and Ts2Cje mice. GAPDH was used as housekeeping gene. (B) Ts2Cje liver section shows an increased fibrotic level. Representative histological images of the rat livers from control and Ts2Cje group. (Top left panel) Mouse liver from control group showing absence of steatosis (score 0) and mild periportal inflammation (score 1) (hematoxylin and eosin; original magnification 100x). (Bottom left panel) Mouse liver from Ts2Cje group exhibiting moderate steatosis (score 2) and moderate portal inflammation (score 2) (hematoxylin and eosin; original magnification 150x). (Mid panel) Mice liver from control group showing absence of fibrosis (score 0) (Masson’s trichrome; original magnification 50x). (Right panel) Mice liver from Ts2Cje group exhibiting diffuse fibrosis (score 3) with fibrous bridging (arrows) (Masson’s trichrome; original magnification 50x). (C) Histological score quantified as in B. Histograms are representative of four different experiments (^*P ≤ 0.05; ^***P ≤ 0.001).