Hyperthyroidism, but not hypertension, impairs PITX2 expression leading to Wnt-microRNA-ion channel remodeling

Abstract

PITX2 is a homeobox transcription factor involved in embryonic left/right signaling and more recently has been associated to cardiac arrhythmias. Genome wide association studies have pinpointed PITX2 as a major player underlying atrial fibrillation (AF). We have previously described that PITX2 expression is impaired in AF patients. Furthermore, distinct studies demonstrate that Pitx2 insufficiency leads to complex gene regulatory network remodeling, i.e. Wnt>microRNAs, leading to ion channel impairment and thus to arrhythmogenic events in mice. Whereas large body of evidences has been provided in recent years on PITX2 downstream signaling pathways, scarce information is available on upstream pathways influencing PITX2 in the context of AF. Multiple risk factors are associated to the onset of AF, such as e.g. hypertension (HTN), hyperthyroidism (HTD) and redox homeostasis impairment. In this study we have analyzed whether HTN, HTD and/or redox homeostasis impact on PITX2 and its downstream signaling pathways. Using rat models for spontaneous HTN (SHR) and experimentally-induced HTD we have observed that both cardiovascular risk factors lead to severe Pitx2 downregulation. Interesting HTD, but not SHR, leads to up-regulation of Wnt signaling as well as deregulation of multiple microRNAs and ion channels as previously described in Pitx2 insufficiency models. In addition, redox signaling is impaired in HTD but not SHR, in line with similar findings in atrial-specific Pitx2 deficient mice. In vitro cell culture analyses using gain- and loss-of-function strategies demonstrate that Pitx2, Zfhx3 and Wnt signaling influence redox homeostasis in cardiomyocytes. Thus, redox homeostasis seems to play a pivotal role in this setting, providing a regulatory feedback loop. Overall these data demonstrate that HTD, but not HTN, can impair Pitx2>>Wnt pathway providing thus a molecular link to AF.

MicroRNA‐133 suppresses ZFHX3‐dependent atrial remodelling and arrhythmia

“…MiR‐195 is a cardio‐miRNA that can elicit hypertrophic cardiomyopathy, dilated cardiomyopathy and heart failure . ZFHX3 can regulate the redox homeostasis in cardiomyocytes . In the present study, we also noted JNK expression after ZFHX3 KD.…”

“…60 ZFHX3 can regulate the redox homeostasis in cardiomyocytes. 61 In the present study, we also noted JNK expression after ZFHX3 KD. JNK signalling initiates physiological changes, resulting in the amplification of reactive oxygen species (ROS) generation.…”

In silico investigation of the mechanisms underlying atrial fibrillation due to impaired Pitx2

“…In the Pitx2-mutant atrial myocytes, a significantly more depolarized resting membrane potential (RMP) [14,15], action potential duration (APD) shortening [10,16,17], and abnormalities in calcium handling [18,19] were observed. Furthermore, expression array analyses identified genes related to calcium handling, gap junctions and ion channels affected by the reduced expression of Pitx2, mediating AF risk in carriers of common gene variants [10,13,14,16,[19][20][21]. However, the precise AF pathophysiology under reduced Pitx2 remains unclear.…”

Interplay between cardiac transcription factors and non-coding RNAs in predisposing to atrial fibrillation

“…In contrast, expression of miR-1 is downregulated in patients with chronic persistent AF [61]. Several lines of experimental evidence suggest that PITX2 also negatively regulates miR-29a expression in atrial myocardium [46,62]. Importantly, a significant increase in the expression levels of miR-29a was observed in both LA [57] and RA [63] appendages from patients with chronic AF compared to those from the sinus rhythm controls.…”