Biology subjects

Hirschi, K. K.

Publications and source records attributed to Hirschi, K. K..

3 recordsLinked to original sources

bioRxiv2021

Distinct Hypoxia-induced Translational Profiles of Embryonic and Adult-derived Macrophages

Tissue homeostasis and repair are orchestrated by resident and newly recruited macrophages that alter their gene expression program in response to changes in tissue microenvironment. Embryonic macrophages, such as fetal liver derived macrophages (FLDM) seed the organs, including heart and lung during embryonic development and persist throughout the adult lifetime, while bone marrow-derived macrophages (BMDM) are recruited following an acute perturbation. Transcriptome analyses of FLDM and BMDM identified differences between them at the level of RNA expression, which correlates imperfectly with protein levels. Post-transcriptional regulation by microRNAs (miRNAs) and RNA-binding proteins determines mRNA stability and translation rate and may override transcriptional cues in response to environmental changes, such as hypoxia. To identify distinct features of FLDM and BMDM response to hypoxia at the level of translation, we employed translating ribosome affinity purification (TRAP) to isolate polysomal RNA. RNA-seq profiling of translated RNA identified distinct hypoxia-induced translational signature of BMDM (Ly6e, vimentin and glycolysis-associated enzymes Pgk1, Tpi1, Aldoa, Ldha) and FLDM (chemokines Ccl7 and Ccl2). By translational profiling of BMDM and FLDM with deletion of the RNA-binding protein HuR, we identified transcripts that were dependent on HuR. These findings highlight the importance of HuR and identify its distinct targets for post-transcriptional regulation of gene expression in embryonic vs. adult-derived macrophages.

cell biology↗

bioRxiv2021

The Cell Surface Receptors Ror1/2 Control Cardiac Myofibroblast Differentiation

BackgroundA hallmark of heart failure is cardiac fibrosis, which results from the injury-induced differentiation response of resident fibroblasts to myofibroblasts that deposit extracellular matrix. During myofibroblast differentiation, fibroblasts progress through polarization stages of early pro-inflammation, intermediate proliferation, and late maturation, but the regulators of this progression are poorly understood. Planar cell polarity receptors, receptor tyrosine kinase like orphan receptor 1 and 2 (Ror1/2), can function to promote cell differentiation and transformation. In this study, we investigated the role of the Ror1/2 in a model of heart failure with emphasis on myofibroblast differentiation. Methods and ResultsThe role of Ror1/2 during cardiac myofibroblast differentiation was studied in cell culture models of primary murine cardiac fibroblast activation and in knockout mouse models that underwent transverse aortic constriction (TAC) surgery to induce cardiac injury by pressure overload. Expression of Ror1 and Ror2 were robustly and exclusively induced in fibroblasts in hearts after TAC surgery, and both were rapidly upregulated after early activation of primary murine cardiac fibroblasts in culture. Cultured fibroblasts isolated from Ror1/2-KO mice displayed a pro-inflammatory phenotype indicative of impaired myofibroblast differentiation. Although the combined ablation of Ror1/2 in mice did not result in a detectable baseline phenotype, TAC surgery led to the death of all mice by day 6 that was associated with myocardial hyper-inflammation and vascular leakage. ConclusionsTogether, these results show that Ror1/2 are essential for the progression of myofibroblast differentiation and for the adaptive remodeling of the heart in response to pressure overload.

cell biology↗

bioRxiv2020

Endothelial Cell Cycle State Determines Propensity for Arterial-Venous Fate

Formation and maturation of a functional blood vascular system is required for the development and maintenance of all tissues in the body. During the process of blood vessel development, primordial endothelial cells are formed and become specified toward arterial or venous fates to generate a circulatory network that provides nutrients and oxygen to, and removes metabolic waste from, all tissues1-3. Specification of arterial and venous endothelial cells occurs in conjunction with suppression of endothelial cell cycle progression4,5, and endothelial cell hyperproliferation is associated with potentially lethal arterial-venous malformations6. However, the mechanistic role that cell cycle state plays in arterial-venous specification is unknown. Herein, studying retinal vascular development in Fucci2aR reporter mice7, we found that venous and arterial endothelial cells are in distinct cell cycle states during development and in adulthood. That is, venous endothelial cells reside in early G1 state, while arterial endothelial cells reside in late G1 state. Endothelial cells in early vs. late G1 exhibited significant differences in gene expression and activity, especially among BMP/TGF-{beta} signaling components. The early G1 state was found to be essential for BMP4-induced venous specification, whereas late G1 state is essential for TGF-{beta}1-induced arterial specification. In a mouse model of endothelial cell hyperproliferation and disrupted vascular remodeling, pharmacological inhibition of endothelial cell cycle rescues the arterial-venous specification defects. Collectively, our results show that endothelial cell cycle control plays a key role in arterial-venous network formation, and distinct cell cycle states provide distinct windows of opportunity for the molecular induction of arterial vs. venous specification.

developmental biology↗