Role of extracellular matrix and mitochondria related genes in determining cardiac defects in Down syndrome

Abstract

Mitochondrial dysfunction, which is consistently observed in Down syndrome (DS), is suspected to worsen mental retardation and congenital cardiopathies in DS subjects, as well as to determine other phenotypic abnormalities, such as Alzheimer's disease, type 2 diabetes, obesity, and hypertrophic cardiopathy. As the heart is one of the main targets of DS, we have analyzed gene expression of DS fetal hearts demonstrating a global downregulation of nuclear encoded mitochondrial genes (NEMGs) together with the upregulation of clusters of extracellular matrix proteins (ECMs). A mitochondrial dysfunction was found associated with NEMG downregulation in DS fetal fibroblasts (DS-HFFs). Based on these previous results, this doctorate thesis was aimed: - to identify Hsa21 genes responsible for either NEMG downregulation or ECM upregulation; - to develop strategies to counteract the negative effects triggered by NEMG dysregulation in DS; - to investigate how NEMG downregulation or ECM upregulation might affect cardiac phenotype. Performing a meta-analysis on public expression data we identified two genes mapping to chromosome 21 (Hsa21), namely NRIP1/ RIP140 (nuclear receptor interacting protein 1) and RUNX1 (Runt related transcription factor 1), as good candidates for NEMG downregulation and ECM upregulation, respectively. These genes are overexpressed in DS cells and in heart tissue. NRIP1 negatively regulates PGC-1α, a master regulator of the mitochondrial function. We attenuated by siRNA NRIP1 expression in a cell model of DS demonstrating an inverse correlation between NRIP1 and PGC-1α expression, together with an improvement of mitochondrial function in silenced cells. We therefore developed a strategy to correct mitochondrial alterations in DS by pharmacologically stimulating the activity of the NRIP1 targets PGC-1α and PPARs. To this aim we supplemented cultures of DS-HFFs with drugs affecting PGC-1α, namely Metformin and Pioglitazone, to evaluate their modulatory impact on mitochondrial function. We found both strategies effective on rescuing mitochondrial function in terms of oxigen consumption, ATP production and mitochondrial biogenesis.