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.

Interstitial lung disease (ILD) is a major cause of morbidity and mortality in scleroderma (systemic sclerosis, or SSc). Fibrocytes are a monocyte-derived cell population implicated in the pathogenesis of fibrosing disorders. Given the recently recognized importance of caveolin-1 in regulating function and signaling in SSc monocytes, in the present study we examined the role of caveolin-1 in the migration and/or trafficking and phenotype of monocytes and fibrocytes in fibrotic lung disease in human patients and an animal model. These studies fill a gap in our understanding of how monocytes and fibrocytes contribute to SSc-ILD pathology. We found that C-X-C chemokine receptor type 4-positive (CXCR4+)/collagen I-positive (ColI+), CD34+/ColI+ and CD45+/ColI+ cells are present in SSc-ILD lungs, but not in control lungs, with CXCR4+ cells being most prevalent. Expression of CXCR4 and its ligand, stromal cell-derived factor 1 (CXCL12), are also highly upregulated in SSc-ILD lung tissue. SSc monocytes, which lack caveolin-1 and therefore overexpress CXCR4, exhibit almost sevenfold increased migration toward CXCL12 compared to control monocytes. Restoration of caveolin-1 function by administering the caveolin scaffolding domain (CSD) peptide reverses this hypermigration. Similarly, transforming growth factor β-treated normal monocytes lose caveolin-1, overexpress CXCR4 and exhibit 15-fold increased monocyte migration that is CSD peptide-sensitive. SSc monocytes exhibit a different phenotype than normal monocytes, expressing high levels of ColI, CD14 and CD34. Because ColI+/CD14+ cells are prevalent in SSc blood, we looked for such cells in lung tissue and confirmed their presence in SSc-ILD lungs but not in normal lungs. Finally, in the bleomycin model of lung fibrosis, we show that CSD peptide diminishes fibrocyte accumulation in the lungs. Our results suggest that low caveolin-1 in SSc monocytes contributes to ILD via effects on cell migration and phenotype and that the hyperaccumulation of fibrocytes in SSc-ILD may result from the altered phenotype and migratory activity of their monocyte precursors.

Objectives-Reduced caveolin-1 levels in scleroderma lung fibroblasts and the lungs of bleomycin-treated mice promote collagen overexpression and lung fibrosis. We now evaluate whether caveolin-1 is deficient in leucocytes from bleomycin-treated mice and scleroderma patients and examine the consequences of this deficiency and its reversal.Methods-Mice or cells received the caveolin-1 scaffolding domain (CSD) peptide to reverse the pathological effects of reduced caveolin-1 expression. In bleomycin-treated mice, we examined caveolin-1 levels in leucocytes and the effect of CSD peptide on leucocyte accumulation in lung tissue. To validate our results in human disease and identify caveolin-1-regulated molecular mechanisms, we isolated monocytes and neutrophils from scleroderma patients and control subjects and evaluated caveolin-1, ERK, JNK, p38, CXCR4, and MMP-9 expression/activation. We also studied these parameters in monocytes treated with cytokines or CSD peptide.Results-Leucocyte caveolin-1 is important in lung fibrosis. In bleomycin-treated mice, caveolin-1 expression is diminished in monocytes and CSD peptide inhibits leucocyte recruitment into the lungs. These observations are relevant to human disease. Scleroderma monocytes and neutrophils contain less caveolin-1 and more activated ERK, JNK, and p38 than their normal counterparts. CSD peptide treatment reverses ERK, JNK, and p38 hyperactivation. Scleroderma monocytes also overexpress CXCR4 and MMP-9. The overexpression of CXCR4 and MMP-9 is inhibited by the CSD peptide. Cytokine treatment of normal monocytes causes adoption of the scleroderma phenotype: low caveolin-1, high CXCR4 and MMP-9, and signaling molecule hyperactivation.Conclusions-Caveolin-1 downregulation in leucocytes contributes to fibrotic lung disease, highlighting caveolin-1 as a promising therapeutic target in scleroderma.

We finely describe the speed of "coming down from infinity" for birth and death processes which eventually become extinct. Under general assumptions on the birth and death rates, we firstly determine the behavior of the successive hitting times of large integers. We put in light two different regimes depending on whether the mean time for the process to go from n + 1 to n is negligible or not compared to the mean time to reach n from infinity. In the first regime, the coming down from infinity is very fast and the convergence is weak. In the second regime, the coming down from infinity is gradual and a law of large numbers and a central limit theorem for the hitting times sequence hold. By an inversion procedure, we deduce that the process is a.s. equivalent to a non-increasing function when the time goes to zero. Our results are illustrated by several examples including applications to population dynamics and population genetics. The particular case where the death rate varies regularly is studied in details.

We review recent results of ours concerning branching processes with general lifetimes and neutral mutations, under the infinitely many alleles model, where mutations can occur either at the birth of particles or at a constant rate during their lives. In both models, we study the allelic partition of the population at time t. We give closed-form formulae for the expected frequency spectrum at t and prove a pathwise convergence to an explicit limit, as t → ∞, of the relative numbers of types younger than some given age and carried by a given number of particles small families . We also provide the convergences in distribution of the sizes or ages of the largest families and of the oldest families. In the case of exponential lifetimes, population dynamics are given by linear birth and death processes, and we can most of the time provide general formulations of our results unifying both models.