Background: Vascular smooth muscle cells (VSMCs) show a remarkable phenotypic plasticity allowing acquisition of contractile or synthetic states but critical information is missing about the physiological signals, promoting formation and maintenance of contractile VSMCs in vivo . BMP9 and BMP10 are known to regulate endothelial quiescence after secretion from the liver and right atrium, whereas a direct role in the regulation of VSMCs was not investigated. Here, we studied the role of BMP9 and BMP10 for controlling formation of contractile VSMCs. Methods: We generated several cell type-specific loss- and gain-of-function transgenic mouse models to investigate the physiological role of BMP9, BMP10, ALK1 and SMAD7 in vivo . Morphometric assessments, expression analysis, blood pressure measurements, single molecule fluorescence in situ hybridization (FISH) were performed together with analysis of isolated pulmonary VSMCs to unravel phenotypic and transcriptomic changes in response to absence or presence of BMP9 and BMP10. Results: Concomitant genetic inactivation of Bmp9 in the germ line and Bmp10 in the right atrium led to dramatic changes in vascular tone and diminution of the VSMC layer with attenuated contractility and decreased systemic as well as right ventricular systolic pressure (RVSP). Vice versa , overexpression of Bmp10 in endothelial cells (ECs) of adult mice dramatically enhanced formation of contractile VSMCs and increased systemic blood pressure as well as RVSP. Likewise, BMP9/10 treatment induced an ALK1-dependent phenotypic switch from synthetic to contractile in pulmonary VSMCs. SMC specific overexpression of Smad7 completely suppressed differentiation and proliferation of VSMCs and reiterated defects observed in adult Bmp9/10 double mutants. Deletion of Alk1 in VSMCs recapitulated the Bmp9/10 phenotype in pulmonary but not in aortic and coronary arteries. Bulk expression analysis and single molecule RNA-FISH uncovered vessel bed-specific, heterogeneous expression of BMP type 1 receptors, explaining phenotypic differences in different Alk1 mutant vessel beds. Conclusions: Our study demonstrates that BMP9 and BMP10 act directly on VSMCs for induction and maintenance of their contractile state. Surprisingly, the effects of BMP9/10 in VSMCs are mediated by different combinations of BMP type 1 receptors in a vessel bed specific manner, offering new opportunities to manipulate blood pressure in the pulmonary circulation.

Mutations in EMD, encoding emerin cause skeletal muscle and heart defects in patients with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) but the underlying mechanisms leading to cardiac defects are poorly understood. Here, we investigated the role of emerin in controlling cardiomyocyte proliferation and cardiac remodeling and explored its function in regulation of the Wnt/β-catenin pathway. We observed a remarkable increase of cardiomyocytes in emerin-null adult mice accompanied with decreased numbers of multinucleated cells. Depletion of emerin in mouse ES cell-derived cardiomyocytes by shRNA caused hyperactivation of Wnt/β-catenin signaling, increased proliferation and abrogated timely cardiac differentiation. Likewise, emerin-null mice exhibited increased Wnt/β-catenin signaling, cardiac dysfunction and perturbed hypertrophic remodeling following pressure overload. Pharmacological inhibition of β-catenin normalized proliferation and differentiation of ES cell-derived cardiomyocytes while inactivation of a single allele of β-catenin efficiently rescued cardiac dysfunction in emerin-null mice. We conclude that emerin constrains β-catenin signaling in the heart providing tight control of cardiomyocyte numbers. Enhanced Wnt/β-catenin signaling seems to contribute to cardiac defects observed in X-EDMD. Hence, therapeutic inhibition of Wnt/β-catenin signaling might be beneficial for X-EDMD patients.

The mechanisms responsible for renal autoregulation continue to arouse considerable interest, and much of the present controversy is centered upon the role of the renin-angiotensin system in modulating the renal hemodynamic response to alterations in renal arterial pressure. Britton proposed a renin-renal autoregulation hypothesis which postulated that plasma angiotensinogen (renin substrate) and converting enzyme interact with cytoplasmic renin at the luminal surfact of the wall of the afferent arteriole to affect the arterial tone (1). In an earlier study, Waugh and Shanks observed that perfusion of isolated kidneys with an artificial colloidal perfusate resulted in loss of autoregulation, while the addition of fresh plasma to the perfusate restored the autoregulatory phenomenon (2). If the renin-angiotensin system is responsible for renal autoregulation and the presence of angiotensin converting enzyme is an essential participant in the autoregulatory process, then the infusion of an angiotensin converting enzyme inhibitor into the renal circulation should modify renal autoregulation. The current study was designed to evaluate the effects on renal autoregulation of limiting the conversion of angiotensin I to angiotensin I1 during a reduction in renal perfusion pressure.Methods. Experiments were performed on 15 female dogs (wt: 19.2 * 1.2 kg) anesthetized with intravenous pentobarbitol (30 mg/ kg) and placed on a positive pressure respirator .l During surgical preparation an infu-sion of Ringers solution was started and approximately 400 ml administered over 2 hr to replace fluid losses. Catheters were introduced into both ureters via a suprapubic incision and a femoral artery was cannulated to withdraw blood samples as well as to monitor blood pressure. The left kidney was exposed through a retroperitoneal flank incision and with a minimum of dissection the aorta, left renal artery and ovarian vein were exposed. A modified Blalock clamp (3) was applied loosely across the aorta cephalad to the right renal artery. The ovarian vein was cannulated with a length of Teflon tubing and the tip advanced to the orifice of the renal vein. The curved shaft of a #25 gauge needle, attached to two lengths of tubing by a ''Y" connection, was inserted into the left renal artery for infusion of 0.9% saline solution, angiotensin I, and angiotensin converting enzyme inhibitor (SQ20881)2 at a rate of 0.5 ml/min. A minimum of 2 hr was allowed to elapse for recovery following the surgical procedures. During this interval appropriate priming and maintenance infusions of p-aminohippurate (PAH) and 1251-iothalamate (Abbott Laboratories, No. Chicago, Ill.) were administered and 30-45 min were allowed for equilibration of these substances before urine collection periods of 20 min duration were started. Blood samples from the femoral artery and renal vein were withdrawn 3 min before the mid point of each period.To determine the effectiveness of the intra-~ ~ ~ ~~

Studies in mice indicate that sex hormones influence the immune system. In general females are more immunocompetent than males and the administration of androgens can suppress antibody formation in females. New Zealand Black (NZB) mice manifest a lack of sex difference in the production of certain autoantibodies and the failure of androgen administration to suppress these antibody levels. To further analyze this phenomenon, androgen receptors were studies in the thymus of NZB and a non-autoimmune strain (C57Bl/6). Specific thymic androgen receptors were found in both NZB and C57Bl/6 mice. The dissociation constant and concentration of specific dihydrotestosterone receptors was determined in thymic cytosol by Scatchard plot analysis. There were no substantial differences in the binding parameters between sexes and between strains. In conclusion, both autoimmune and control strains have similar high affinity thymic androgen receptors. Therefore, the immune androgen insensitivity observed in NZB mice is not the result of a lack of high affinity thymic androgen receptors.