Primary Cilia of the Cardiac Neural Crest Orchestrate Critical Aspects of Ventricular Maturation and Postnatal Cardiac Function: A Role for Hedgehog Signaling

Primary cilia are tiny, plasma-membrane bound organelles that function to modulate intra- and extracellular signaling, in particular Hedgehog signaling, implicated in both normal development as well as in various disease pathologies, including congenital heart disease (CHD). Cardiac neural crest cells (CNCC) display primary cilia and function as a major progenitor cell population contributing to the developing heart. We hypothesized that damage to or loss of primary cilia in CNCC would impair normal heart development, leading to CHD. We present 1) a precise description of CHD’s resulting from loss of primary cilia of CNCC in vivo ; 2) characterization of the functional, electrophysiological aspects of the perinatal phenotype; and 3) a preliminary investigation of the molecular mechanisms leading to this phenotype. Using a Wnt1:Cre-2, Ift88-targeted conditional elimination of primary cilia, and a Td-tomato reporter to track CNCC, we observed loss of cilia in CNCC at embryonic day E9.5, with notable CNCC contribution to the ventricular myocardium and pronounced disorganization of the endocardium by E10.5.The phenotype resulting from cilia loss in CNCC was characterized by a variety predicted CHDs in addition to disorganization of the ventricular endocardium, pronounced noncompaction of the ventricular myocardium, and perinatal lethality. To investigate potential changes in Hedgehog signaling resulting from cilia loss, we implemented an in vivo conditional knockout in which Wnt1:Cre-2 drives expression of a mutant, constitutively-active Hedgehog receptor. Noncompaction observed in all Wnt1:Cre-2/Ift88 mutants became exacerbated in a primary-cilia dependent fashion with the introduction of forced Hedgehog signaling in CNCC. These results support a critical role for both primary cilia and Hedgehog signaling in the development of the ventricular myocardium. Further electrophysiological assessments of Wnt1:Cre-2/Ift88 newborn mutant mice revealed bradycardia, conduction defects, and ECG tracings consistent with ventricular hypertrophy. These data collectively support a role for Hedgehog signaling via primary cilia of CNCC in the pathogenesis of outflow tract defects, VSD, and most notably, ventricular maturation CHDs.