Ablation of C-type natriuretic peptide/cGMP signaling in fibroblasts exacerbates adverse cardiac remodeling in mice.

Excessive activation of cardiac fibroblasts (CFs) in response to injury provokes cardiac fibrosis, stiffness, and failure. The local mediators counterregulating this response remain unclear. Exogenous C-type natriuretic peptide (CNP) exerts antifibrotic effects in preclinical models. To unravel the role of the endogenous hormone, we generated mice with fibroblast-restricted deletion (KO) of guanylyl cyclase-B (GC-B), the cGMP-synthesizing CNP receptor. CNP activated GC-B/cGMP signaling in human and murine CFs, preventing proliferative and promigratory effects of angiotensin II (Ang II) and TGF-ß. Fibroblast-specific GC-B-KO mice showed enhanced fibrosis in response to Ang II infusions. Moreover, after 2 weeks of mild pressure overload induced by transverse aortic constriction (TAC), such KO mice had augmented cardiac fibrosis and hypertrophy, together with systolic and diastolic contractile dysfunction. This was associated with increased expression of the profibrotic genes encoding collagen I, III, and periostin. Notably, such responses to Ang II and TAC were greater in female as compared with male KO mice. Enhanced Ang II-induced CNP expression in female hearts and augmented GC-B expression and activity in female CFs may contribute to this sex disparity. The results show that paracrine CNP signaling in CFs has antifibrotic and antihypertrophic effects. The CNP/GC-B/cGMP pathway might be a target for therapies combating pathological cardiac remodeling.

Stabilization of Perivascular Mast Cells by Endothelial CNP (C-Type Natriuretic Peptide).

OBJECTIVE: Activated perivascular mast cells (MCs) participate in different cardiovascular diseases. Many factors provoking MC degranulation have been described, while physiological counterregulators are barely known. Endothelial CNP (C-type natriuretic peptide) participates in the maintenance of vascular barrier integrity, but the target cells and mechanisms are unclear. Here, we studied whether MCs are regulated by CNP. Approach and Results: In cultured human and murine MCs, CNP activated its specific GC (guanylyl cyclase)-B receptor and cyclic GMP signaling. This enhanced cyclic GMP-dependent phosphorylation of the cytoskeleton-associated VASP (vasodilator-stimulated phosphoprotein) and inhibited ATP-evoked degranulation. To elucidate the relevance in vivo, mice with a floxed GC-B (Npr2) gene were interbred with a Mcpt5-CreTG line to generate mice lacking GC-B in connective tissue MCs (MC GC-B knockout). In anesthetized mice, acute ischemia-reperfusion of the cremaster muscle microcirculation provoked extensive MC degranulation and macromolecule extravasation. Superfusion of CNP markedly prevented MC activation and endothelial barrier disruption in control but not in MC GC-B knockout mice. Notably, already under resting conditions, such knockout mice had increased numbers of degranulated MCs in different tissues, together with elevated plasma chymase levels. After transient coronary occlusion, their myocardial areas at risk and with infarction were enlarged. Moreover, MC GC-B knockout mice showed augmented perivascular neutrophil infiltration and deep vein thrombosis in a model of inferior vena cava ligation. CONCLUSIONS: CNP, via GC-B/cyclic GMP signaling, stabilizes resident perivascular MCs at baseline and prevents their excessive activation under pathological conditions. Thereby CNP contributes to the maintenance of vascular integrity in physiology and disease.

ß Cell-specific deletion of guanylyl cyclase A, the receptor for atrial natriuretic peptide, accelerates obesity-induced glucose intolerance in mice.

BACKGROUND: The cardiac hormones atrial (ANP) and B-type natriuretic peptides (BNP) moderate arterial blood pressure and improve energy metabolism as well as insulin sensitivity via their shared cGMP-producing guanylyl cyclase-A (GC-A) receptor. Obesity is associated with impaired NP/GC-A/cGMP signaling, which possibly contributes to the development of type 2 diabetes and its cardiometabolic complications. In vitro, synthetic ANP, via GC-A, stimulates glucose-dependent insulin release from cultured pancreatic islets and ß-cell proliferation. However, the relevance for systemic glucose homeostasis in vivo is not known. To dissect whether the endogenous cardiac hormones modulate the secretory function and/or proliferation of ß-cells under (patho)physiological conditions in vivo, here we generated a novel genetic mouse model with selective disruption of the GC-A receptor in ß-cells. METHODS: Mice with a floxed GC-A gene were bred to Rip-CreTG mice, thereby deleting GC-A selectively in ß-cells (ß GC-A KO). Weight gain, glucose tolerance, insulin sensitivity, and glucose-stimulated insulin secretion were monitored in normal diet (ND)- and high-fat diet (HFD)-fed mice. ß-cell size and number were measured by immunofluorescence-based islet morphometry. RESULTS: In vitro, the insulinotropic and proliferative actions of ANP were abolished in islets isolated from ß GC-A KO mice. Concordantly, in vivo, infusion of BNP mildly enhanced baseline plasma insulin levels and glucose-induced insulin secretion in control mice. This effect of exogenous BNP was abolished in ß GC-A KO mice, corroborating the efficient inactivation of the GC-A receptor in ß-cells. Despite this under physiological, ND conditions, fasted and fed insulin levels, glucose-induced insulin secretion, glucose tolerance and ß-cell morphology were similar in ß GC-A KO mice and control littermates. However, HFD-fed ß GC-A KO animals had accelerated glucose intolerance and diminished adaptative ß-cell proliferation. CONCLUSIONS: Our studies of ß GC-A KO mice demonstrate that the cardiac hormones ANP and BNP do not modulate ß-cell's growth and secretory functions under physiological, normal dietary conditions. However, endogenous NP/GC-A signaling improves the initial adaptative response of ß-cells to HFD-induced obesity. Impaired ß-cell NP/GC-A signaling in obese individuals might contribute to the development of type 2 diabetes.

Polycomb Protein BMI1 Regulates Osteogenic Differentiation of Human Adipose Tissue-Derived Mesenchymal Stem Cells Downstream of GSK3.

Polycomb proteins such as the B lymphoma Mo-MLV insertion region 1 homolog (BMI1) are essential chromatin factors for the self-renewal and differentiation of embryonic and adult stem cells. BMI1 also plays a critical role in osteogenesis as Bmi1-deficient mice display a skeletal phenotype caused by the exhaustion of the mesenchymal stem cell pool. In this study, we have studied the role of BMI1 in the osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells (hASCs). BMI1 protein, but not RNA levels, increases during in vitro osteogenic differentiation of hASCs. Overexpression of BMI1 leads to an osteogenic priming of hASCs under nondifferentiating conditions and enhanced osteogenesis upon differentiation, along with increased BMP2 and WNT11 expressions. Conversely, knockdown of BMI1 expression reduces osteogenic differentiation. Furthermore, our studies indicate that during osteogenic differentiation of hASCs, BMI1 is a downstream target of GSK3 signaling. BMI1, therefore, acts as a pro-osteogenic differentiation factor in hASCs and hence it is a promising target for active modulation of hASC-derived osteogenesis.

Expression of B-RAF V600E in type II pneumocytes causes abnormalities in alveolar formation, airspace enlargement and tumor formation in mice.

Growth factor induced signaling cascades are key regulatory elements in tissue development, maintenance and regeneration. Perturbations of these cascades have severe consequences, leading to developmental disorders and neoplastic diseases. As a major function in signal transduction, activating mutations in RAF family kinases are the cause of human tumorigenesis, where B-RAF V600E has been identified as the prevalent mutant. In order to address the oncogenic function of B-RAF V600E, we have generated transgenic mice expressing the activated oncogene specifically in lung alveolar epithelial type II cells. Constitutive expression of B-RAF V600E caused abnormalities in alveolar epithelium formation that led to airspace enlargements. These lung lesions showed signs of tissue remodeling and were often associated with chronic inflammation and low incidence of lung tumors. The inflammatory cell infiltration did not precede the formation of the lung lesions but was rather accompanied with late tumor development. These data support a model where the continuous regenerative process initiated by oncogenic B-RAF-driven alveolar disruption provides a tumor-promoting environment associated with chronic inflammation.

MYC is a metastasis gene for non-small-cell lung cancer.

BACKGROUND: Metastasis is a process by which cancer cells learn to form satellite tumors in distant organs and represents the principle cause of death of patients with solid tumors. NSCLC is the most lethal human cancer due to its high rate of metastasis. METHODOLOGY/PRINCIPAL FINDINGS: Lack of a suitable animal model has so far hampered analysis of metastatic progression. We have examined c-MYC for its ability to induce metastasis in a C-RAF-driven mouse model for non-small-cell lung cancer. c-MYC alone induced frank tumor growth only after long latency at which time secondary mutations in K-Ras or LKB1 were detected reminiscent of human NSCLC. Combination with C-RAF led to immediate acceleration of tumor growth, conversion to papillary epithelial cells and angiogenic switch induction. Moreover, addition of c-MYC was sufficient to induce macrometastasis in liver and lymph nodes with short latency associated with lineage switch events. Thus we have generated the first conditional model for metastasis of NSCLC and identified a gene, c-MYC that is able to orchestrate all steps of this process. CONCLUSIONS/SIGNIFICANCE: Potential markers for detection of metastasis were identified and validated for diagnosis of human biopsies. These markers may represent targets for future therapeutic intervention as they include genes such as Gata4 that are exclusively expressed during lung development.

Use of a recombinant Salmonella enterica serovar Typhimurium strain expressing C-Raf for protection against C-Raf induced lung adenoma in mice.

BACKGROUND: Serine-threonine kinases of the Raf family (A-Raf, B-Raf, C-Raf) are central players in cellular signal transduction, and thus often causally involved in the development of cancer when mutated or over-expressed. Therefore these proteins are potential targets for immunotherapy and a possible basis for vaccine development against tumors. In this study we analyzed the functionality of a new live C-Raf vaccine based on an attenuated Salmonella enterica serovar Typhimurium aroA strain in two Raf dependent lung tumor mouse models. METHODS: The antigen C-Raf has been fused to the C-terminal secretion signal of Escherichia coli alpha-hemolysin and expressed in secreted form by an attenuated aroA Salmonella enterica serovar Typhimurium strain via the alpha-hemolysin secretion pathway. The effect of the immunization with this recombinant C-Raf strain on wild-type C57BL/6 or lung tumor bearing transgenic BxB mice was analyzed using western blot and FACS analysis as well as specific tumor growth assays. RESULTS: C-Raf antigen was successfully expressed in secreted form by an attenuated Salmonella enterica serovar Typhimurium aroA strain using the E. coli hemolysin secretion system. Immunization of wild-type C57BL/6 or tumor bearing mice provoked specific C-Raf antibody and T-cell responses. Most importantly, the vaccine strain significantly reduced tumor growth in two transgenic mouse models of Raf oncogene-induced lung adenomas. CONCLUSIONS: The combination of the C-Raf antigen, hemolysin secretion system and Salmonella enterica serovar Typhimurium could form the basis for a new generation of live bacterial vaccines for the treatment of Raf dependent human malignancies.

B-Raf specific antibody responses in melanoma patients.

BACKGROUND: Mutations of the BRAF gene are the most common genetic alteration in melanoma. Moreover, BRAF mutations are already present in benign nevi. Being overexpressed and mutated, B-Raf is a potential target for the immune system and as this mutation seems to be an early event, a humoral immune response against this antigen might serve as a diagnostic tool for detection of high risk patients. METHODS: 372 sera of 148 stage IV melanoma patients and 119 sera of non-melanoma patients were screened for B-Raf, B-Raf V599E and C-Raf specific antibodies by an ELISA assay. Sera were screened for specific total Ig and for IgG. Serum titers were compared with a two tailed Mann-Whitney U test. Sera with titers of 1:300 or higher were termed positive and groups were compared with a two tailed Fisher's exact test. RESULTS: B-Raf specific antibodies recognizing both B-Raf and B-Raf V599E were detected in 8.9% of the sera of melanoma patients and in 2,5% of the control group. Raf specific IgG was detected in some patients at very low levels. B-Raf specific antibody responses did not correlate with clinical parameters but in some cases, B-Raf antibodies emerged during disease progression. CONCLUSION: These findings imply that B-Raf is immunogenic in melanoma patients and that it might serve as a potential target for immunotherapy. However, B-Raf specific antibodies emerge at rather late stages of melanoma progression and are present only with a low frequency indicating that spontaneous B-Raf specific antibodies are not an early marker for melanoma, but rather may serve as a therapeutic target.