Endothelial cells drive organ fibrosis in mice by inducing expression of the transcription factor SOX9.

Fibrosis is a hallmark of chronic disease. Although fibroblasts are involved, it is unclear to what extent endothelial cells also might contribute. We detected increased expression of the transcription factor Sox9 in endothelial cells in several different mouse fibrosis models. These models included systolic heart failure induced by pressure overload, diastolic heart failure induced by high-fat diet and nitric oxide synthase inhibition, pulmonary fibrosis induced by bleomycin treatment, and liver fibrosis due to a choline-deficient diet. We also observed up-regulation of endothelial SOX9 in cardiac tissue from patients with heart failure. To test whether SOX9 induction was sufficient to cause disease, we generated mice with endothelial cell-specific overexpression of Sox9, which promoted fibrosis in multiple organs and resulted in signs of heart failure. Endothelial Sox9 deletion prevented fibrosis and organ dysfunction in the two mouse models of heart failure as well as in the lung and liver fibrosis mouse models. Bulk and single-cell RNA sequencing of mouse endothelial cells across multiple vascular beds revealed that SOX9 induced extracellular matrix, growth factor, and inflammatory gene expression, leading to matrix deposition by endothelial cells. Moreover, mouse endothelial cells activated neighboring fibroblasts that then migrated and deposited matrix in response to SOX9, a process partly mediated by the secreted growth factor CCN2, a direct SOX9 target; endothelial cell-specific Sox9 deletion reversed these changes. These findings suggest a role for endothelial SOX9 as a fibrosis-promoting factor in different mouse organs during disease and imply that endothelial cells are an important regulator of fibrosis.

C1q and Tumor Necrosis Factor Related Protein 9 Protects from Diabetic Cardiomyopathy by Alleviating Cardiac Insulin Resistance and Inflammation.

(1) Background: Diabetic cardiomyopathy is a major health problem worldwide. CTRP9, a secreted glycoprotein, is mainly expressed in cardiac endothelial cells and becomes downregulated in mouse models of diabetes mellitus; (2) Methods: In this study, we investigated the impact of CTRP9 on early stages of diabetic cardiomyopathy induced by 12 weeks of high-fat diet; (3) Results: While the lack of CTRP9 in knock-out mice aggravated insulin resistance and triggered diastolic left ventricular dysfunction, AAV9-mediated cardiac CTRP9 overexpression ameliorated cardiomyopathy under these conditions. At this early disease state upon high-fat diet, no fibrosis, no oxidative damage and no lipid deposition were identified in the myocardium of any of the experimental groups. Mechanistically, we found that CTRP9 is required for insulin-dependent signaling, cardiac glucose uptake in vivo and oxidative energy production in cardiomyocytes. Extensive RNA sequencing from myocardial tissue of CTRP9-overexpressing and knock-out as well as respective control mice revealed that CTRP9 acts as an anti-inflammatory mediator in the myocardium. Hence, CTRP9 knock-out exerted more, while CTRP9-overexpressing mice showed less leukocytes accumulation in the heart during high-fat diet; (4) Conclusions: In summary, endothelial-derived CTRP9 plays a prominent paracrine role to protect against diabetic cardiomyopathy and might constitute a therapeutic target.

Acid sensing ion channels in rat cerebral arteries: Probing the expression pattern and vasomotor activity.

AIMS: The recent identification of acid sensing ion channels (ASICs) in vascular beds suggests their possible involvement in modulating vasomotor tone. Therefore, we investigated the gene expression profiles of ASIC subtypes in the middle cerebral artery (MCA) of Wistar rats and the functional implication of ASICs in acidosis-induced relaxation as well as maintenance of resting tension. MAIN METHODS: Real time PCR was employed to study the pattern of ASIC mRNA expression in the MCA wall in comparison with (i) matching brain tissue samples and (ii) arteries cultured for 24 h and 48 h. The functional implication regarding vasomotor response to acidosis and maintenance of resting tension was assessed using in vitro myography. KEY FINDINGS: A robust mRNA expression of ASIC-1, -2 and -4 was found in brain tissue samples and to a lower extent in freshly isolated MCA. In the MCA wall, short term culture induced a down-regulation of ASIC-1 and -2 expression without any remarkable change in ASIC-4 expression. Acidosis induced a pH-related relaxation of freshly isolated MCA ring segments, being more pronounced after short term culture. Incubation with the ASIC blocker amiloride moderately enhanced acidosis-induced relaxation, in cultured MCAs somewhat stronger than in freshly isolated vessels. In addition, amiloride resulted in a decrease of resting tension, albeit only in freshly isolated MCA. SIGNIFICANCE: Our results comprehensively describe ASIC subtype composition in the rat MCA in physiological and pathological conditions and strongly suggest the involvement of ASICs in the modulation of vasomotor responses under conditions of normal or decreased pH values.

Enhancement of bradykinin-induced relaxation by focal brain ischemia in the rat middle cerebral artery: Receptor expression upregulation and activation of multiple pathways.

Focal brain ischemia markedly affects cerebrovascular reactivity. So far, these changes have mainly been related to alterations in the level of smooth muscle cell function while alterations of the endothelial lining have not yet been studied in detail. We have, therefore, investigated the effects of ischemia/reperfusion injury on bradykinin (BK)-induced relaxation since BK is an important mediator of tissue inflammation and affects vascular function in an endothelium-dependent manner. Focal brain ischemia was induced in rats by endovascular filament occlusion (2h) of the middle cerebral artery (MCA). After 22h reperfusion, both MCAs were harvested and the response to BK studied in organ bath experiments. Expression of the BK receptor subtypes 1 and 2 (B1, B2) was determined by real-time semi-quantitative RT-qPCR methodology, and whole mount immunofluorescence staining was performed to show the B2 receptor protein expression. In control animals, BK did not induce significant vasomotor effects despite a functionally intact endothelium and robust expression of B2 mRNA. After ischemia/reperfusion injury, BK induced a concentration-related sustained relaxation in all arteries studied, more pronounced in the ipsilateral than in the contralateral MCA. The B2 mRNA was significantly upregulated and the B1 mRNA displayed de novo expression, again more pronounced ipsi- than contralaterally. Endothelial cells displaying B2 receptor immunofluorescence were observed scattered or clustered in previously occluded MCAs. Relaxation to BK was mediated by B2 receptor activation, abolished after endothelium denudation, and largely diminished by blocking nitric oxide (NO) release or soluble guanylyl cyclase activity. Relaxation to BK was partially inhibited by charybdotoxin (ChTx), but not apamin or iberiotoxin suggesting activation of an endothelium-dependent hyperpolarization pathway. When the NO-cGMP pathway was blocked, BK induced a transient relaxation which was suppressed by ChTx. After ischemia/reperfusion injury BK elicits endothelium-dependent relaxation which was not detectable in control MCAs. This gain of function is mediated by B2 receptor activation and involves the release of NO and activation of an endothelium-dependent hyperpolarization. It goes along with increased B2 mRNA and protein expression, leaving the functional role of the de novo B1 receptor expression still open.

A novel method to isolate retinal and brain microvessels from individual rats: Microscopic and molecular biological characterization and application in hyperglycemic animals.

Alterations in the retinal microvessel (RMV) compartment occurring in systemic disease states such as diabetes may eventually contribute to blindness. To specifically address the pathophysiological role of the microvasculature we developed a new method for RMV bulk isolation from individual rats. The extraction procedure performed in the cold throughout takes less than one hour. Slight modifications enable isolation of brain microvessels (BMVs) for comparison. Microscopically, RMVs and BMVs consisted mainly of capillaries of good structural integrity. The endothelial cell/pericyte ratio was approximately 1.8 in RMVs and 2.7 in BMVs, well in agreement with data from intact vascular beds. Total RNA extracted from individual rats amounted to approximately 7 ng in RMVs, 50 ng in BMVs, and 155 ng in pial arteries (which were also isolated) with highly preserved integrity throughout. Measurements using microfluidic card methodology revealed segregation of RMVs, BMVs, and pial arteries in distinct clusters based on principal component analysis. In all three vascular compartments endothelial cell-specific markers were significantly enriched. Similarly, pericyte-specific markers displayed accumulation in RMVs, BMVs, and pial arteries, the latter probably reflecting the common ontogenetic origin of pericytes and smooth muscle cells. Isolation of RMVs, BMVs, and pial arteries from rats suffering from 8-weeks hyperglycemia yielded expression patterns of endothelial cell- and pericyte-specific marker genes largely comparable to those obtained in control rats. Our newly developed protocols allow for selective studies of RMVs from individual rats to characterize reactive pathways, in comparison with the ontogenetically closely related BMVs. Moreover, our protocols with inclusion of pial arteries enable comparative studies of the macro- and microvasculature from the same organ.

Early administration of a second-generation perfluorochemical decreases ischemic brain damage in a model of permanent middle cerebral artery occlusion in the rat.

OBJECTIVES: Perfluorochemicals (PFCs) may exert a neuroprotective function in the early phase of ischemia by improving the oxygen supply to the endangered tissue. We have, therefore, investigated the effect of Oxycyte, a second-generation perfluorocarbon solution, on the extent of early ischemic brain damage in a model of permanent focal cerebral ischemia. METHODS: Eight hours of permanent focal cerebral ischemia was induced in isoflurane anesthetized male Sprague-Dawley rats by unilateral middle cerebral artery (MCA) thread occlusion under the control of laser Doppler flowmetry (LDF). Animals were assigned to one of the following treatment groups: nO2-NaCl and hO2-NaCl-NaCl (0.9%, 1 ml/100 g i.v.) and nO2-Oxycyte and hO2-Oxycyte-Oxycyte (1 ml/100 g i.v.). The injection of NaCl or Oxycyte was performed immediately after MCA occlusion. After injection, breathing was changed to pure oxygen in groups hO2-NaCl and hO2-Oxycyte while animals in groups nO2-NaCl and nO2-Oxycyte were allowed to breathe air. The necrotic volume was calculated from serial coronal sections stained with silver-nitrate. In addition, nitrotyrosine production was studied by immunohistochemistry. RESULTS: Upon MCA occlusion, animals showed a reduction of cerebral blood flow of approximately 80% of the LDF signal in all groups. Hemodynamic and metabolic parameters were not affected by the infusion of Oxycyte. The total infarct volume was reduced in hO2-Oxycyte animals [group nO2-NaCl: 341+/-31 mm3 (mean+/-SD), group hO2-NaCl: 351+/-33 mm3, group nO2-Oxycyte: 354+/-24 mm3, and group hO2-Oxycyte: 300+/-29 mm3, p < 0.05 versus all other groups]. Moreover, hO2-Oxycyte animals showed lesser intensity of nitrotyrosine staining when compared with hO2-NaCl animals. DISCUSSION: These results suggest that Oxycyte administered immediately after the onset of vascular occlusion may exert neuroprotective effects in the early phase of brain ischemia.