Resident fibroblast lineages mediate pressure overload–induced cardiac fibrosis

Activation and accumulation of cardiac fibroblasts, which result in excessive extracellular matrix deposition and consequent mechanical stiffness, myocyte uncoupling, and ischemia, are key contributors to heart failure progression. Recently, endothelial-to-mesenchymal transition (EndoMT) and the recruitment of circulating hematopoietic progenitors to the heart have been reported to generate substantial numbers of cardiac fibroblasts in response to pressure overload–induced injury; therefore, these processes are widely considered to be promising therapeutic targets. Here, using multiple independent murine Cre lines and a collagen1a1-GFP fusion reporter, which specifically labels fibroblasts, we found that following pressure overload, fibroblasts were not derived from hematopoietic cells, EndoMT, or epicardial epithelial-to-mesenchymal transition. Instead, pressure overload promoted comparable proliferation and activation of two resident fibroblast lineages, including a previously described epicardial population and a population of endothelial origin. Together, these data present a paradigm for the origins of cardiac fibroblasts during development and in fibrosis. Furthermore, these data indicate that therapeutic strategies for reducing pathogenic cardiac fibroblasts should shift from targeting presumptive EndoMT or infiltrating hematopoietically derived fibroblasts, toward common pathways upregulated in two endogenous fibroblast populations.     

BM mesenchymal stromal cell–derived exosomes facilitate multiple myeloma progression

BM mesenchymal stromal cells (BM-MSCs) support multiple myeloma (MM) cell growth, but little is known about the putative mechanisms by which the BM microenvironment plays an oncogenic role in this disease. Cell-cell communication is mediated by exosomes. In this study, we showed that MM BM-MSCs release exosomes that are transferred to MM cells, thereby resulting in modulation of tumor growth in vivo. Exosomal microRNA (miR) content differed between MM and normal BM-MSCs, with a lower content of the tumor suppressor miR-15a. In addition, MM BM-MSC–derived exosomes had higher levels of oncogenic proteins, cytokines, and adhesion molecules compared with exosomes from the cells of origin. Importantly, whereas MM BM-MSC–derived exosomes promoted MM tumor growth, normal BM-MSC exosomes inhibited the growth of MM cells. In summary, these in vitro and in vivo studies demonstrated that exosome transfer from BM-MSCs to clonal plasma cells represents a previously undescribed and unique mechanism that highlights the contribution of BM-MSCs to MM disease progression.     

Cardiac fibroblasts mediate IL-17A–driven inflammatory dilated cardiomyopathy

Inflammatory dilated cardiomyopathy (DCMi) is a major cause of heart failure in individuals below the age of 40. We recently reported that IL-17A is required for the development of DCMi. We show a novel pathway connecting IL-17A, cardiac fibroblasts (CFs), GM-CSF, and heart-infiltrating myeloid cells with the pathogenesis of DCMi. Il17ra^−/− mice were protected from DCMi, and this was associated with significantly diminished neutrophil and Ly6Chi monocyte/macrophage (MO/MΦ) cardiac infiltrates. Depletion of Ly6Chi MO/MΦ also protected mice from DCMi. Mechanistically, IL-17A stimulated CFs to produce key chemokines and cytokines that are critical downstream effectors in the recruitment and differentiation of myeloid cells. Moreover, IL-17A directs Ly6Chi MO/MΦ in trans toward a more proinflammatory phenotype via CF-derived GM-CSF. Collectively, this IL-17A–fibroblast–GM-CSF–MO/MΦ axis could provide a novel target for the treatment of DCMi and related inflammatory cardiac diseases.Inflammatory dilated cardiomyopathy (DCMi) is among the most common causes of noncongenital heart failure in individuals under the age of 40 (Dimas et al., 2009). There has been only limited success with symptomatic therapy in chronic DCMi patients, leaving cardiac transplantation the only cure for end stage heart failure secondary to DCMi (Pietra et al., 2012). Autoimmunity to heart tissue is often involved in the pathogenesis of DCMi (Čiháková and Rose, 2008; Cooper, 2009). In an effort to investigate the immunopathologic mechanism responsible for DCMi in humans, we have adopted a mouse model of experimental autoimmune myocarditis (EAM). EAM is induced by immunization of genetically susceptible BALB/c mice with a peptide derived from the cardiac myosin heavy chain α (MyHCα_614-629). Immunized mice develop myocarditis characterized by inflammatory infiltration peaking about day 21, and subsequently progress to DCMi around day 40 to day 70, characterized by cardiac fibrosis and impairment of cardiac function (Čiháková et al., 2004).EAM is a CD4⁺ T helper cell–dependent disease (Smith and Allen, 1991, 1993). One of the CD4⁺ T helper cell subsets, Th17 cells, has been observed to infiltrate the heart during EAM (Baldeviano et al., 2010), and has been reported to be critical in autoimmunity (Korn et al., 2009). Furthermore, patients with DCMi have increased numbers of Th17 cells in their blood and an elevated level of Th17 cytokines in serum, suggesting that Th17 cells are involved in the pathogenesis of DCMi (Ding et al., 2010; Yuan et al., 2010). When we examined whether the hallmark Th17 cytokine, IL-17A, drives the pathogenesis of myocarditis, we discovered that Il17a^−/− mice were completely protected from the development of DCMi, although they had myocardial inflammation comparable in overall severity to WT controls (Baldeviano et al., 2010). Thus, IL-17A is dispensable for early stage myocarditis but required for the progression to DCMi. These results indicated a critical role of IL-17A in driving cardiac damage and fibrosis during the development of DCMi. Similar profibrotic functions of IL-17A have been reported in cirrhosis (Lan et al., 2009) and fibrotic lung injury (Wilson et al., 2010) models.Monocytes (MOs) and macrophages (MΦs) are key effector cells during inflammatory processes (Gordon and Taylor, 2005) including myocarditis and DCMi. MO/MΦs comprise about half of all heart-infiltrating inflammatory cells at the peak of EAM and play important roles in the pathogenesis (Čiháková et al., 2008; Barin et al., 2012). Monocytes arise from hematopoietic stem cells and form distinct subpopulations. In mouse, the two monocyte subsets, CCR2^hiCX3CR1^loLy6C^hi and CCR2^loCX3CR1^hiLy6C^lo monocytes, infiltrate sites of inflammation responding to different chemokine signals and differentiate into inflammatory MΦs guided by local cytokine signals (Gordon and Taylor, 2005; Shi and Pamer, 2011). The balance between MO/MΦ subsets and their differentiation is critical in determining the pathogenic outcome in immune responses (Wynn et al., 2013). In this paper, while examining the pathogenic mechanisms of IL-17A–dependent DCMi, we describe a novel immunological pathway connecting IL-17A with MO/MΦs that drives DCMi development.     

Tumor fibroblast–derived epiregulin promotes growth of colitis-associated neoplasms through ERK

Molecular mechanisms specific to colitis-associated cancers have been poorly characterized. Using comparative whole-genome expression profiling, we observed differential expression of epiregulin (EREG) in mouse models of colitis-associated, but not sporadic, colorectal cancer. Similarly, EREG expression was significantly upregulated in cohorts of patients with colitis-associated cancer. Furthermore, tumor-associated fibroblasts were identified as a major source of EREG in colitis-associated neoplasms. Functional studies showed that Ereg-deficient mice, although more prone to colitis, were strongly protected from colitis-associated tumors. Serial endoscopic studies revealed that EREG promoted tumor growth rather than initiation. Additionally, we demonstrated that fibroblast-derived EREG requires ERK activation to induce proliferation of intestinal epithelial cells (IEC) and tumor development in vivo. To demonstrate the functional relevance of EREG-producing tumor-associated fibroblasts, we developed a novel system for adoptive transfer of these cells via mini-endoscopic local injection. It was found that transfer of EREG-producing, but not Ereg-deficient, fibroblasts from tumors significantly augmented growth of colitis-associated neoplasms in vivo. In conclusion, our data indicate that EREG and tumor-associated fibroblasts play a crucial role in controlling tumor growth in colitis-associated neoplasms.     

Cardiac Nerve Growth Factor Overexpression Induces Bone Marrow–derived Progenitor Cells Mobilization and Homing to the Infarcted Heart

Reparative response by bone marrow (BM)-derived progenitor cells (PCs) to ischemia is a multistep process that comprises the detachment from the BM endosteal niche through activation of osteoclasts and proteolytic enzymes (such as matrix metalloproteinases (MMPs)), mobilization to the circulation, and homing to the injured tissue. We previously showed that intramyocardial nerve growth factor gene transfer (NGF-GT) promotes cardiac repair following myocardial infarction (MI) in mice. Here, we investigate the impact of cardiac NGF-GT on postinfarction BM-derived PCs mobilization and homing at different time points after adenovirus-mediated NGF-GT in mice. Immunohistochemistry and flow cytometry newly illustrate the temporal profile of osteoclast and activation of MMP9, PCs expansion in the BM, and liberation/homing to the injured myocardium. NGF-GT amplified these responses and increased the BM levels of active osteoclasts and MMP9, which were not observed in MMP9-deficient mice. Taken together, our results suggest a novel role for NGF in BM-derived PCs mobilization/homing following MI.