Microglia Control Vascular Architecture via a TGFβ1 Dependent Paracrine Mechanism Linked to Tissue Mechanics

© 2020, The Author(s). Tissue microarchitecture and mechanics are important in development and pathologies of the Central Nervous System (CNS); however, their coordinating mechanisms are unclear. Here, we report that during colonization of the retina, microglia contacts the deep layer of high stiffness, which coincides with microglial bipolarization, reduction in TGFβ1 signaling and termination of vascular growth. Likewise, stiff substrates induce microglial bipolarization and diminish TGFβ1 expression in hydrogels. Both microglial bipolarization in vivo and the responses to stiff substrates in vitro require intracellular adaptor Kindlin3 but not microglial integrins. Lack of Kindlin3 causes high microglial contractility, dysregulation of ERK signaling, excessive TGFβ1 expression and abnormally-patterned vasculature with severe malformations in the area of photoreceptors. Both excessive TGFβ1 signaling and vascular defects caused by Kindlin3-deficient microglia are rescued by either microglial depletion or microglial knockout of TGFβ1 in vivo. This mechanism underlies an interplay between microglia, vascular patterning and tissue mechanics within the CNS

Abstract 15509: <i>SYNE2</i> Expression Regulates Calcium Cycling and Mitochondria Function in Cardiomyocytes: Implications for Association With Atrial Fibrillation

Introduction: SYNE2 encodes a nuclear membrane protein that connects the nucleus with the cytoskeleton. rs1152591 is a common SNP in the SYNE2 gene that is associated with atrial fibrillation (AF) and with reduced expression of SYNE2α1 , a short isoform, in human left atrial appendage tissue. We previously found that SYNE2α1 over expression (OE) acts as a dominant negative for the nuclear phenotype, similar to the SYNE2 knockdown (KD), leading to enlarged nuclear size and decreased nuclear stiffness. Objectives: To determine if GFP- SYNE2α1 (OE) and KD of all SYNE2 isoforms show similar effects on gene expression and cell physiology in human induced pluripotent stem cell-derived cardiomyocytes (iCMs). Methods and Results: RNAseq after SYNE2α1 OE or SYNE2 KD revealed both congruent changes in expression of specific genes, supporting the dominant negative role of SYNE2α1 , but also divergent changes in expression of some genes, showing specific effects of the SYNE2α1 short isoform. We identified both mitochondrial function and sarcoplasmic reticulum (SR) function as differentially expressed pathways comparing OE vs. KD iCMs. Fura-2 photometry was used to study Ca 2+ cycling in beating iCMs, and revealed delayed calcium reuptake in the SYNE2 KD cells (15.9% increase in reuptake time as % of each contraction, p&lt;0.0001), but not in the GFP- SYNE2α1 OE cells (not significant). Flow cytometry showed significantly lower SERCA2 expression in the SYNE2 KD cells but not in the SYNE2α1 OE cells (12% decrease, p=0.029). Immunofluorescence microscopy revealed that GFP-SYNE2α1 not only localized to the nuclear membrane but also to the SR, stained with anti-SERCA2. Flow cytometry after MitoTracker Orange staining, to monitor the cellular volume of functional mitochondria, was significantly increased in both the SYNE2α1 OE and SYNE2 KD iCMs vs. their respective controls. Thus, despite differential expression of mitochondrial pathway genes, SYNE2α1 mimics the KD of all SYNE2 isoforms in regard to mitochondrial function. Conclusions: SYNE2α1 OE, unlike KD of all SYNE2 isoforms, preserves SR Ca 2+ reuptake activity, and this may contribute to the mechanism by which the AF risk allele in the SYNE2 gene, associated with decreased expression of SYNE2α1, predisposes carriers to AF. </jats:p

Cardiac overexpression of microRNA-7 is associated with adverse cardiac remodeling

AbstractRole of microRNA-7 (miRNA-7) in targeting Epidermal growth factor receptor (EGFR/ERBB) family is known in dividing cancer cells while less is known about its role in terminally differentiated cardiac cells. We generated transgenic (Tg) mice with cardiomyocyte-specific overexpression of miRNA-7 to determine its role in regulating cardiac function. Despite similar survival, expression of miRNA-7 results in cardiac dilation as measured by echocardiography, instead of age-based cardiac hypertrophy observed in littermate controls. In contrast to the classical adaptive hypertrophy in response to TAC, miRNA-7 Tg mice directly undergo cardiac dilation post-TAC that is associated with increased fibrosis. Interestingly, significant loss in ERBB2 expression was observed in cardiomyocytes with no changes in ERBB1 (EGFR). Gene ontology and cellular component analysis using the cardiac proteomics data showed significant reduction in mitochondrial membrane integrity reflecting the differential enrichment/loss of proteins in miRNA-7 Tg mice compared to littermate controls. Consistently, electron microscopy showed that miRNA-7 Tg hearts had disorganized and rounded mitochondrial morphology indicating mitochondrial dysfunction. These findings show that expression of miRNA-7 uniquely results in cardiac dilation instead of adaptive hypertrophic response to cardiac stress providing insights on adverse remodeling in physiology and pathology.</jats:p

Abstract 16716: Comparison of Blood Troponin I Complexes and Free Form in Acute Myocardial Infarction and End Stage Renal Disease

Introduction: Circulating blood troponin complexes and free fractions remain poorly characterised in different conditions where troponin is detectable in blood Hypothesis: The aim of the study was to compare the differences in troponin-I(TnI) complexes/free-forms in end stage renal disease (ESRD) compared to acute myocardial infarction(AMI) Methods: Blood was collected from patients with AMI(n=7) or ESRD(n=4) at two time points (a)As early as possible after AMI or at initial contact with ESRD patients and (b)24-48 hours later. Western blotting was carried out with HyTest cTnI-560cc antibody on plasma extracted from whole blood. Densitometry analysis was performed and evaluated using the independent samples T-test and paired T-test as appropriate Results: Prominent bands were noted at ~45,~37 and ~25 kDa respectively representing low molecular weight(LMW) TnI-TnT-TnC complex, binary TnI-TnC complex and free-TnI. At time-point (a), there was no difference in these bands between STEMI and CKD patients. Interestingly, at time-point (b), AMI patients had significantly lower intensity of the 45kDa and 37kDa bands compared to CKD patients(for 45 kDa band mean difference was 54.3±19.4 AU, p=0.02; for 37 kDa band mean difference was 27.7±10.5 AU, p=0.03) as well as compared to the initial STEMI samples taken at time-point (a)(for 45 kDa band mean difference was 41.4±8.1 AU, p=0.002; for 37 kDa band mean difference was 16.7±6.3 AU, p=0.002) ,however there was no difference in the 25kDa band Conclusions: AMI patients had progressively lesser quantities of circulating LMW-ITC and binary IC complexes following AMI compared to ESRD patients, but similar quantities of circulating free TnI. This indicates a constant release of LMW-ITC and binary-IC complexes from the myocardium or reduced glomerular filtration of these complexes in ESRD while in the AMI patients, the LMW-ITC and binary I-C complexes appear to be progressively eliminated from plasma after the initial release </jats:p

Insulin inhibits protein phosphatase 2A to impair β-adrenergic receptor function

AbstractInsulin impairs β2-adrenergic receptor (β2AR) function through G protein-coupled receptor kinase 2 (GRK2) by phosphorylation but less is known about dephosphorylation mechanisms mediated by protein phosphatase 2A (PP2A). Pharmacologic or genetic inhibition of phosphoinositide 3-kinase γ (PI3Kγ) unexpectedly resulted in significant reduction of insulin-mediated β2AR phosphorylation. Interestingly, β2AR-associated phosphatase activity was inhibited by insulin but was reversed by knock-down of PI3Kγ showing negative regulation of PP2A by PI3Kγ. Co-immunoprecipitation and surface plasmon resonance studies using purified proteins showed that GRK2 and PI3Kγ form a complex and could be recruited to β2ARs as GRK2 interacts with insulin receptor substrate following insulin treatment. Consistently, β-blocker pretreatment did not reduce insulin-mediated β2AR phosphorylation indicating agonist- and Gβγ-independent non-canonical regulation of receptor function. Mechanistically, PI3Kγ inhibits PP2A activity at the βAR complex by phosphorylating an intracellular inhibitor of PP2A (I2PP2A). Knock-down or CRISPR ablation of endogenous I2PP2A unlocked PP2A inhibition mediating β2AR dephosphorylation showing an unappreciated acute regulation of PP2A in mediating insulin-β2AR cross-talk.SummaryInsulin impairs β2-adrenergic receptor (β2AR) function through G protein-coupled receptor kinase 2 (GRK2). We show that insulin simultaneously inhibits protein phosphatase 2A (PP2A) sustaining β2AR functional impairment. Unexpectedly, releasing PP2A inhibition by PI3Kγ preserves β2AR function despite intact insulin-driven GRK2-mechanisms.</jats:sec

Microglia control vascular architecture via a TGFβ1 dependent paracrine mechanism linked to tissue mechanics

AbstractTissue microarchitecture and mechanics are important in development and pathologies of the Central Nervous System (CNS); however, their coordinating mechanisms are unclear. Here, we report that during colonization of the retina, microglia contacts the deep layer of high stiffness, which coincides with microglial bipolarization, reduction in TGFβ1 signaling and termination of vascular growth. Likewise, stiff substrates induce microglial bipolarization and diminish TGFβ1 expression in hydrogels. Both microglial bipolarization in vivo and the responses to stiff substrates in vitro require intracellular adaptor Kindlin3 but not microglial integrins. Lack of Kindlin3 causes high microglial contractility, dysregulation of ERK signaling, excessive TGFβ1 expression and abnormally-patterned vasculature with severe malformations in the area of photoreceptors. Both excessive TGFβ1 signaling and vascular defects caused by Kindlin3-deficient microglia are rescued by either microglial depletion or microglial knockout of TGFβ1 in vivo. This mechanism underlies an interplay between microglia, vascular patterning and tissue mechanics within the CNS.</jats:p

Cardiac expression of microRNA-7 is associated with adverse cardiac remodeling

AbstractAlthough microRNA-7 (miRNA-7) is known to regulate proliferation of cancer cells by targeting Epidermal growth factor receptor (EGFR/ERBB) family, less is known about its role in cardiac physiology. Transgenic (Tg) mouse with cardiomyocyte-specific overexpression of miRNA-7 was generated to determine its role in cardiac physiology and pathology. Echocardiography on the miRNA-7 Tg mice showed cardiac dilation instead of age-associated physiological cardiac hypertrophy observed in non-Tg control mice. Subjecting miRNA-7 Tg mice to transverse aortic constriction (TAC) resulted in cardiac dilation associated with increased fibrosis bypassing the adaptive cardiac hypertrophic response to TAC. miRNA-7 expression in cardiomyocytes resulted in significant loss of ERBB2 expression with no changes in ERBB1 (EGFR). Cardiac proteomics in the miRNA-7 Tg mice showed significant reduction in mitochondrial membrane structural proteins compared to NTg reflecting role of miRNA-7 beyond the regulation of EGFR/ERRB in mediating cardiac dilation. Consistently, electron microscopy showed that miRNA-7 Tg hearts had disorganized rounded mitochondria that was associated with mitochondrial dysfunction. These findings show that expression of miRNA-7 in the cardiomyocytes results in cardiac dilation instead of adaptive hypertrophic response during aging or to TAC providing insights on yet to be understood role of miRNA-7 in cardiac function.</jats:p

βArrestins in Cardiac G Protein-Coupled Receptor Signaling and Function: Partners in Crime or “Good Cop, Bad Cop”?

βarrestin (βarr)-1 and -2 (βarrs) (or Arrestin-2 and -3, respectively) are universal G protein-coupled receptor (GPCR) adapter proteins expressed abundantly in extra-retinal tissues, including the myocardium. Both were discovered in the lab of the 2012 Nobel Prize in Chemistry co-laureate Robert Lefkowitz, initially as terminators of signaling from the β-adrenergic receptor (βAR), a process known as functional desensitization. They are now known to switch GPCR signaling from G protein-dependent to G protein-independent, which, in the case of βARs and angiotensin II type 1 receptor (AT1R), might be beneficial, e.g., anti-apoptotic, for the heart. However, the specific role(s) of each βarr isoform in cardiac GPCR signaling and function (or dysfunction in disease), remain unknown. The current consensus is that, whereas both βarr isoforms can desensitize and internalize cardiac GPCRs, they play quite different (even opposing in certain instances) roles in the G protein-independent signaling pathways they initiate in the cardiovascular system, including in the myocardium. The present review will discuss the current knowledge in the field of βarrs and their roles in GPCR signaling and function in the heart, focusing on the three most important, for cardiac physiology, GPCR types (β1AR, β2AR &amp; AT1R), and will also highlight important questions that currently remain unanswered