Suppression of angiotensin II-induced pathological changes in heart and kidney by the caveolin-1 scaffolding domain peptide.

Dysregulation of the renin-angiotensin system leads to systemic hypertension and maladaptive fibrosis in various organs. We showed recently that myocardial fibrosis and the loss of cardiac function in mice with transverse aortic constriction (TAC) could be averted by treatment with the caveolin-1 scaffolding domain (CSD) peptide. Here, we used angiotensin II (AngII) infusion (2.1 mg/kg/day for 2 wk) in mice as a second model to confirm and extend our observations on the beneficial effects of CSD on heart and kidney disease. AngII caused cardiac hypertrophy (increased heart weight to body weight ratio (HW/BW) and cardiomyocyte cross-sectional area); fibrosis in heart and kidney (increased levels of collagen I and heat shock protein-47 (HSP47)); and vascular leakage (increased levels of IgG in heart and kidney). Echocardiograms of AngII-infused mice showed increased left ventricular posterior wall thickness (pWTh) and isovolumic relaxation time (IVRT), and decreased ejection fraction (EF), stroke volume (SV), and cardiac output (CO). CSD treatment (i.p. injections, 50 µg/mouse/day) of AngII-infused mice significantly suppressed all of these pathological changes in fibrosis, hypertrophy, vascular leakage, and ventricular function. AngII infusion increased ß1 and ß3 integrin levels and activated Pyk2 in both heart and kidney. These changes were also suppressed by CSD. Finally, bone marrow cell (BMC) isolated from AngII-infused mice showed hyper-migration toward SDF1. When AngII-infused mice were treated with CSD, BMC migration was reduced to the basal level observed in cells from control mice. Importantly, CSD did not affect the AngII-induced increase in blood pressure (BP), indicating that the beneficial effects of CSD were not mediated via normalization of BP. These results strongly indicate that CSD suppresses AngII-induced pathological changes in mice, suggesting that CSD can be developed as a treatment for patients with hypertension and pressure overload-induced heart failure.

Fibrocytes in the fibrotic lung: altered phenotype detected by flow cytometry.

Fibrocytes are bone marrow hematopoietic-derived cells that also express a mesenchymal cell marker (commonly collagen I) and participate in fibrotic diseases of multiple organs. Given their origin, they or their precursors must be circulating cells before recruitment into target tissues. While most previous studies focused on circulating fibrocytes, here we focus on the fibrocyte phenotype in fibrotic tissue. The study's relevance to human disease is heightened by use of a model in which bleomycin is delivered systemically, recapitulating several features of human scleroderma including multi-organ fibrosis not observed when bleomycin is delivered directly into the lungs. Using flow cytometry, we find in the fibrotic lung a large population of CD45(high) fibrocytes (called Region I) rarely found in vehicle-treated control mice. A second population of CD45+ fibrocytes (called Region II) is observed in both control and fibrotic lung. The level of CD45 in circulating fibrocytes is far lower than in either Region I or II lung fibrocytes. The chemokine receptors CXCR4 and CCR5 are expressed at higher levels in Region I than in Region II and are present at very low levels in all other lung cells including CD45+/collagen I- leucocytes. The collagen chaperone HSP47 is present at similar high levels in both Regions I and II, but at a higher level in fibrotic lung than in control lung. There is also a major population of HSP47(high)/CD45- cells in fibrotic lung not present in control lung. CD44 is present at higher levels in Region I than in Region II and at much lower levels in all other cells including CD45+/collagen I- leucocytes. When lung fibrosis is inhibited by restoring caveolin-1 activity using a caveolin-1 scaffolding domain peptide (CSD), a strong correlation is observed between fibrocyte number and fibrosis score. In summary, the distinctive phenotype of fibrotic lung fibrocytes suggests that fibrocyte differentiation occurs primarily within the target organ.

Bleomycin delivery by osmotic minipump: similarity to human scleroderma interstitial lung disease.

The interstitial lung diseases (ILD) include a large number of chronic, progressive, irreversible respiratory disorders involving pulmonary fibrosis, the most common of which are idiopathic pulmonary fibrosis and scleroderma lung disease (SSc ILD). Because bleomycin causes lung fibrosis when used in cancer chemotherapy, it is used to model human ILD in rodents. In most studies, bleomycin has been delivered directly into the lung by intratracheal or intraoral administration. Here we have compared the effects in mice of bleomycin delivered directly into the lungs (direct model) or systemically using osmotic minipumps (pump model) to determine which more closely resembles human ILD. The pump model is more similar to human SSc ILD in that: 1) lung injury/fibrosis is limited to the subpleural portion of the lung in the pump model and in SSc ILD, whereas the entire lung is affected in the direct model; 2) conversely, there is massive inflammation throughout the lung in the direct model, whereas inflammation is limited in the pump model and in SSc ILD; 3) hypertrophic type II alveolar epithelial cells are present at high levels in SSc ILD and in the pump model but not in the direct model; and 4) lung fibrosis is accompanied by dermal fibrosis. The pump model is also move convenient and humane than the direct model because there is less weight loss and mortality.

Antifibrotic properties of caveolin-1 scaffolding domain in vitro and in vivo.

Lung fibrosis involves the overexpression of ECM proteins, primarily collagen, by alpha-smooth muscle actin (ASMA)-positive cells. Caveolin-1 is a master regulator of collagen expression by cultured lung fibroblasts and of lung fibrosis in vivo. A peptide equivalent to the caveolin-1 scaffolding domain (CSD peptide) inhibits collagen and tenascin-C expression by normal lung fibroblasts (NLF) and fibroblasts from the fibrotic lungs of scleroderma patients (SLF). CSD peptide inhibits ASMA expression in SLF but not NLF. Similar inhibition of collagen, tenascin-C, and ASMA expression was also observed when caveolin-1 expression was upregulated using adenovirus. These observations suggest that the low caveolin-1 levels in SLF cause their overexpression of collagen, tenascin-C, and ASMA. In mechanistic studies, MEK, ERK, JNK, and Akt were hyperactivated in SLF, and CSD peptide inhibited their activation and altered their subcellular localization. These studies and experiments using kinase inhibitors suggest many differences between NLF and SLF in signaling cascades. To validate these data, we determined that the alterations in signaling molecule activation observed in SLF also occur in fibrotic lung tissue from scleroderma patients and in mice with bleomycin-induced lung fibrosis. Finally, we demonstrated that systemic administration of CSD peptide to bleomycin-treated mice blocks epithelial cell apoptosis, inflammatory cell infiltration, and changes in tissue morphology as well as signaling molecule activation and collagen, tenascin-C, and ASMA expression associated with lung fibrosis. CSD peptide may be a prototype for novel treatments for human lung fibrosis that act, in part, by inhibiting the expression of ASMA and ECM proteins.