Chiriac, Anca

Abstract Genomic perturbations that challenge normal signaling at the pluripotent stage may trigger unforeseen ontogenic aberrancies. Anticipatory systems biology identification of transcriptome landscapes that underlie latent phenotypes would offer molecular diagnosis before the onset of symptoms. The purpose of this study was to assess the impact of calreticulin-deficient embryonic stem cell transcriptomes on molecular functions and physiological systems. Bioinformatic surveillance of calreticulin-null stem cells, a monogenic insult model, diagnosed a disruption in transcriptome dynamics, which re-prioritized essential cellular functions. Calreticulin-calibrated signaling axes were uncovered, and network-wide cartography of undifferentiated stem cell transcripts suggested cardiac manifestations. Calreticulin-deficient stem cell-derived cardiac cells verified disorganized sarcomerogenesis, mitochondrial paucity, and cytoarchitectural aberrations to validate calreticulin-dependent network forecasts. Furthermore, magnetic resonance imaging and histopathology detected a ventricular septal defect, revealing organogenic manifestation of calreticulin deletion. Thus, bioinformatic deciphering of a primordial calreticulin-deficient transcriptome decoded at the pluripotent stem cell stage a reconfigured multifunctional molecular registry to anticipate predifferentiation susceptibility toward abnormal cardiophenotype.

Rationale: Tissue factor pathway inhibitor (TFPI) is a potent regulator of the tissue factor pathway and is found in plasma in association with lipoproteins. Objective: To determine the role of TFPI in the development of atherosclerosis, we bred mice which overexpress TFPI into the apolipoprotein E–deficient (apoE −/− ) background. Methods and Results: On a high-fat diet, smooth muscle 22α (SM22α)-TFPI/apoE −/− mice were shown to have less aortic plaque burden compared to apoE −/− mice. Unexpectedly, SM22α-TFPI/apoE −/− had lower plasma cholesterol levels compared to apoE −/− mice. Furthermore, SM22α-TFPI mice fed a high-fat diet had lower cholesterol levels than did wild-type mice. Because TFPI is associated with lipoproteins and its carboxyl terminus (TFPIct) has been shown to be a ligand for the very-low-density lipoprotein (VLDL) receptor, we hypothesized that TFPI overexpression may regulate lipoprotein distribution. We quantified VLDL binding and uptake in vitro in mouse aortic smooth muscle cells from SM22α-TFPI and wild-type mice. Mouse aortic smooth muscle cells from SM22α-TFPI mice demonstrated higher VLDL binding and internalization compared to those from wild-type mice. Because SM22α-TFPI mice have increased circulating levels of TFPI antigen, we examined whether TFPIct may act to alter lipoprotein distribution. In vitro, TFPIct increased VLDL binding, uptake, and degradation in murine embryonic fibroblasts. Furthermore, this effect was blocked by heparinase treatment. In vivo, systemic administration of TFPIct reduced plasma cholesterol levels in apoE −/− mice. Conclusions: These studies suggest that overexpression of TFPI lowers plasma cholesterol through the interaction of its carboxyl terminus with lipoproteins and heparan sulfate proteoglycans.

Abstract Pluripotent stem cells demonstrate an inherent propensity for unrestricted multi-lineage differentiation. Translation into regenerative applications requires identification and isolation of tissue-specified progenitor cells. From a comprehensive pool of 11,272 quality-filtered genes, profiling embryonic stem cells at discrete stages of cardiopoiesis revealed 736 transcripts encoding membrane-associated proteins, where 306 were specifically upregulated with cardiogenic differentiation. Bioinformatic dissection of exposed surface biomarkers prioritized the chemokine receptor cluster as the most significantly over-represented gene receptor family during pre cardiac induction, with CXCR4 uniquely associated with mesendoderm formation. CXCR4+ progenitors were sorted from the embryonic stem cell pool into mesoderm-restricted progeny according to co-expression with the early mesoderm marker Flk-1. In contrast to CXCR4−/Flk-1− cells, the CXCR4+/Flk-1+ subpopulation demonstrated overexpressed cardiac lineage transcription factors (Mef2C, Myocardin, Nkx2.5), whereas pluripotent genes (Oct4, Fgf4, Sox2) as well as neuroectoderm (Sox1) and endoderm alpha-fetoprotein markers were all depleted. In fact, the CXCR4+/Flk-1+ biomarker combination identified embryonic stem cell progeny significantly enriched with Mesp-1, GATA-4, and Tbx5, indicative of pre cardiac mesoderm and the primary heart field. Although the CXCR4+/Flk-1+ transcriptome shared 97% identity with the CXCR4−/Flk-1− counterpart, the 818 divergent gene set represented predominantly cardiovascular developmental functions and formed a primitive cardiac network. Differentiation of CXCR4+/Flk-1+ progenitors yielded nuclear translocation of myocardial transcription factors and robust sarcomerogenesis with nascent cardiac tissue demonstrating beating activity and calcium transients. Thus, the CXCR4/Flk-1 biomarker pair predicts the emergence of cardiogenic specification within a pluripotent stem cell pool, enabling targeted selection of cardiopoietic lineage. Disclosure of potential conflicts of interest is found at the end of this article.