Pax8 and Nkx2-1 haploinsufficiencies differentially affect liver metabolic pathways

Abstract

Thyroid dysfunctions are associated with liver diseases ranging, in severity, from insulin resistance (IR) to hepatocellular carcinoma. The pathogenic mechanisms appear complex and are not attributable, exclusively, to the impaired thyroid hormone (TH) signalling. Using a mouse model of human congenital hypothyroidism, young double heterozygote for both NK2 homeobox 1 (Nkx2-1)- and Paired box 8 (Pax8)-null mutations (DHTP) mice, and single heterozygous Pax8+/− and Nkx2-1+/− mice, we studied the liver pathways, the endocrine and metabolic factors affected in conditions of different dysthyroidisms. Young Nkx2-1+/− females displayed a slight hyperthyroidism and, in liver, increased TH signalling (i.e. increased expression of Dio1 and Trβ1) and lipogenic gene expression, with triglycerides accumulation. Hypothyroid DHTP and euthyroid Pax8+/− females shared liver and skeletal muscle IR and hepatic hypothyroidism (i.e. reduced expression of Mct8, Dio1 and TRβ1), activation of AKT and increased expression of glutathione peroxidase 4. Oxidative stress and reduced mitochondrial COX activity were observed in DHTP mice only. Pax8+/− females, but, unexpectedly, not DHTP ones, displayed transcriptional activation of the hepatic (and renal) gluconeogenic pathway, hypercortisolemia, fasting hyperglycaemia and hyperinsulinemia, reduced serum β-hydroxybutyrate, associated with hepatic AMPK activation. DHTP mice showed hypercholesterolemia and activation of mTOR. Collectively, the data indicate that heterozygote mutations of Pax8 and Nkx2-1 genes may produce multiple dysmetabolisms, even under systemic euthyroidism. Differential liver pathways and multiple hormonal axes are affected with implications for energy and nutrient homeostasis. The identified players may be specific target in the management of thyroid dysfunction-associated dysmetabolisms in terms of prevention/counteraction of IR, type 2 diabetes and related comorbidities.