Genetic Fate Mapping Identifies Second Heart Field Progenitor Cells As a Source of Adipocytes in Arrhythmogenic Right Ventricular Cardiomyopathy

Abstract

Abstract-The phenotypic hallmark of arrhythmogenic right ventricular cardiomyopathy, a genetic disease of desmosomal proteins, is fibroadipocytic replacement of the right ventricle. Cellular origin of excess adipocytes, the responsible mechanism(s) and the basis for predominant involvement of the right ventricle are unknown. We generated 3 sets of lineage tracer mice regulated by cardiac lineage promoters ␣-myosin heavy chain (␣MyHC), Nkx2.5, or Mef2C. We conditionally expressed the reporter enhanced yellow fluorescent protein while concomitantly deleting the desmosomal protein desmoplakin in cardiac myocyte lineages using the Cre-LoxP technique. Lineage tracer mice showed excess fibroadiposis and increased numbers of adipocytes in the hearts. Few adipocytes in the hearts of ␣MyHC-regulated lineage tracer mice, but the majority of adipocytes in the hearts of Nkx2.5-and Mef2C-regulated lineage tracer mice, expressed enhanced yellow fluorescent protein. In addition, rare cells coexpressed adipogenic transcription factors and the second heart field markers Isl1 and Mef2C in the lineage tracer mouse hearts and in human myocardium from patients with arrhythmogenic right ventricular cardiomyopathy. To delineate the responsible mechanism, we generated transgenic mice expressing desmosomal protein plakoglobin in myocyte lineages. Transgene plakoglobin translocated to nucleus, detected by immunoblotting and immunofluorescence staining and coimmunoprecipitated with Tcf7l2, a canonical Wnt signaling transcription factor. Expression levels of canonical Wnt/Tcf7l2 targets bone morphogenetic protein 7 and Wnt5b, which promote adipogenesis, were increased and expression level of connective tissue growth factor, an inhibitor of adipogenesis, was decreased. We conclude adipocytes in arrhythmogenic right ventricular cardiomyopathy originate from the second heart field cardiac progenitors, which switch to an adipogenic fate because of suppressed canonical Wnt signaling by nuclear plakoglobin. Key Words: adipocytes Ⅲ progenitor cells Ⅲ Wnt signaling Ⅲ desmosomes Ⅲ heart failure A rrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic disease characterized by the unique phenotype of fibroadipocytic replacement of cardiac myocytes, predominantly in the right ventricle. [1][2][3] Clinical manifestations of ARVC include ventricular arrhythmias, typically originating from the right ventricle; sudden cardiac death, which often is its first manifestation; and right ventricular aneurysmal dilatation and failure. 1,4 The left ventricle is also commonly involved in the advanced stages. 1,5 ARVC is typically an autosomal dominant disease. Recessive forms in conjunction with palmoplantar keratoderma and woolly hair (Naxos disease) or predominant involvement of the left ventricle (Carvajal syndrome) are referred to as "cardiocutaneous syndromes." 6,7 Recently, mutations in 5 genes for ARVC, namely, DSP, JUP, PKP2, DSC2, and DSG2, encoding desmosomal proteins desmoplakin (Dsp), plakoglobin (PG), plakophilin 2, desmocollin 2, and ...

Maturation-Based Model of Arrhythmogenic Right Ventricular Dysplasia Using Patient-Specific Induced Pluripotent Stem Cells

“…27 The same group of researchers also used genetic fate mapping techniques in mouse ARVD models to indicate that islet-1 positive (Isl1 + ) cardiac progenitor cells are the source of adipocytes in ARVD hearts. 34 However, misuse of terminologies for adipogenesis and later conflicting data from other groups [30][31][32] argue against the validity of this Pkg-β-catenin hypothesis. First, activation of peroxisome proliferator-activated receptor-γ (PPAR γ ) and its target genes was used as the marker for "adipogenesis (adipocyte formation)", which is absolutely incorrect and misleading.…”

“…First, activation of peroxisome proliferator-activated receptor-γ (PPAR γ ) and its target genes was used as the marker for "adipogenesis (adipocyte formation)", which is absolutely incorrect and misleading. 27, 34 In fact, PPAR γ and its target genes are normally activated in several non-adipocyte tissues (eg, endothelial cells and macrophages), and could be abnormally activated by pathological conditions in liver (fatty livers) and CMs (diabetic cardiomyopathy). 35 Therefore, activation of PPAR γ and its target genes indicates the active process of "de novo lipogenesis" rather than cell transdifferentiation toward adipocytes.…”

Loss of plakophilin 2 disrupts heart development in zebrafish

“…The replacement of cardiac myocytes by fibrous and fatty tissue is also characteristic of ARVC. This likely involves differentiation of cardiac progenitor cells to adipocytes, a process that can be caused by suppression of canonical Wnt signalling (Lombardi et al, 2009). We and others have shown that plakoglobin, another armadillo protein, is inhibitory to Wnt signalling and its knockdown reduces the number of desmosomes in the intercalated discs (Martin et al, 2009;Lombardi et al, 2009).…”

Arrhythmogenic Cardiomyopathy

“…Noteworthy, SB216763 was already known as an activator of the canonical Wnt signaling pathway and this study confirms an abnormal protein trafficking at the intercalated discs, rather than altered protein production in AC. These data, together with those by Lombardi et al [96] and by Kim et al [99], who were able to prevent cell degenerative changes using another Wnt activator, i.e. 6-bromoindirubin-3'-oxime, open the door to the identification of a curative therapy in AC, by targeting a final common pathway of disease pathogenesis.…”

“…Knockdown of DSP in HL-1 cells causes the translocation of JUP into the nucleus, where it interferes with β-catenin/TCF transcriptional activity, leading to an adipogenic switch. Thereafter, by using genetic fate-mapping methods, the same group demonstrated that most of the adipocytes in AC originate from cardiac progenitors cells of the embryonic second heart field [96]. Furthermore, in mice overexpressing cardiac truncated JUP, suppression of the canonical Wnt signaling pathway and induction of proadipogenic genes expression due to nuclear translocation of JUP led to adipogenesis in c-kit + cardiac progenitor cells [97].…”