Deletion of periostin reduces muscular dystrophy and fibrosis in mice by modulating the transforming growth factor-β pathway

The muscular dystrophies are broadly classified as muscle wasting diseases with myofiber dropout due to cellular necrosis, inflammation, alterations in extracellular matrix composition, and fatty cell replacement. These events transpire and progress despite ongoing myofiber regeneration from endogenous satellite cells. The degeneration/regeneration response to muscle injury/disease is modulated by the proinflammatory cytokine transforming growth factor-β (TGF-β), which can also profoundly influence extracellular matrix composition through increased secretion of profibrotic proteins, such as the matricellular protein periostin. Here we show that up-regulation and secretion of periostin is pathological and enhances disease in the δ-sarcoglycan null (Sgcd(−/−)) mouse model of muscular dystrophy (MD). Indeed, MD mice lacking the Postn gene showed dramatic improvement in skeletal muscle structure and function. Mechanistically, Postn gene deletion altered TGF-β signaling so that it now enhanced tissue regeneration with reduced levels of fibrosis. Systemic antagonism of TGF-β with a neutralizing monoclonal antibody mitigated the beneficial effects of Postn deletion in vivo. These data suggest that periostin functions as a disease determinant in MD by promoting/allowing the pathological effects of TGF-β, suggesting that inhibition of periostin could represent a unique treatment approach

Desmoplakin is Important for Proper Cardiac Cell-Cell Interactions

Normal cardiac function is maintained through dynamic interactions of cardiac cells with each other and with the extracellular matrix. These interactions are important for remodeling during cardiac growth and pathophysiological conditions. However, the precise mechanisms of these interactions remain unclear. In this study we examined the importance of desmoplakin (DSP) in cardiac cell-cell interactions. Cell-cell communication in the heart requires the formation and preservation of cell contacts by cell adhesion junctions called desmosome-like structures. A major protein component of this complex is DSP, which plays a role in linking the cytoskeletal network to the plasma membrane. Our laboratory previously generated a polyclonal antibody (1611) against the detergent soluble fraction of cardiac fibroblast plasma membrane. In attempting to define which proteins 1611 recognizes, we performed two-dimensional electrophoresis and identified DSP as one of the major proteins recognized by 1611. Immunoprecipitation studies demonstrated that 1611 was able to directly pulldown DSP. We also demonstrate that 1611 and anti-DSP antibodies co-localize in whole heart sections. Finally, using a three-dimensional in vitro cell-cell interaction assay, we demonstrate that 1611 can inhibit cell-cell interactions. These data indicate that DSP is an important protein for cell-cell interactions and affects a variety of cellular functions, including cytokine secretion

Pressure Overload Induces Early Morphological Changes in the Heart

Cardiac hypertrophy, whether pathological or physiological, induces a variety of additional morphological and physiological changes in the heart, including altered contractility and hemodynamics. Events exacerbating these changes are documented during later stages of hypertrophy (usually termed pathological hypertrophy). Few studies document the morphological and physiological changes during early physiological hypertrophy. We define acute cardiac remodeling events in response to transverse aortic constriction (TAC), including temporal changes in hypertrophy, collagen deposition, capillary density, and the cell populations responsible for these changes. Cardiac hypertrophy induced by TAC in mice was detected 2 days after surgery (as measured by heart weight, myocyte width, and wall thickness) and peaked by day 7. Picrosirius staining revealed increased collagen deposition 7 days after TAC; immunostaining and flow cytometry indicated a concurrent increase in fibroblasts. The findings correlated with angiogenesis in TAC hearts; a decrease in capillary density was observed at day 2, with recovery to sham-surgery levels by day 7. Increased pericyte levels, which were observed 2 days after TAC, may mediate this angiogenic transition. Gene expression suggests a coordinated response in growth, extracellular matrix, and angiogenic factors to mediate the observed morphological changes. Our data demonstrate that morphological changes in response to cardiovascular injury occur rapidly, and the present findings allow correlation of specific events that facilitate these changes

IL-6 loss causes ventricular dysfunction, fibrosis, reduced capillary density, and dramatically alters the cell populations of the developing and adult heart

Interleukin-6 (IL-6) is a pleiotropic cytokine responsible for many different processes including the regulation of cell growth, apoptosis, differentiation, and survival in various cell types and organs, including the heart. Recent studies have indicated that IL-6 is a critical component in the cell-cell communication between myocytes and cardiac fibroblasts. In this study, we examined the effects of IL-6 deficiency on the cardiac cell populations, cardiac function, and interactions between the cells of the heart, specifically cardiac fibroblasts and myocytes. To examine the effects of IL-6 loss on cardiac function, we used the IL-6−/− mouse. IL-6 deficiency caused severe cardiac dilatation, increased accumulation of interstitial collagen, and altered expression of the adhesion protein periostin. In addition, flow cytometric analyses demonstrated dramatic alterations in the cardiac cell populations of IL-6−/− mice compared with wild-type littermates. We observed a marked increase in the cardiac fibroblast population in IL-6−/− mice, whereas a concomitant decrease was observed in the other cardiac cell populations examined. Moreover, we observed increased cell proliferation and apoptosis in the developing IL-6−/− heart. Additionally, we observed a significant decrease in the capillary density of IL-6−/− hearts. To elucidate the role of IL-6 in the interactions between cardiac fibroblasts and myocytes, we performed in vitro studies and demonstrated that IL-6 deficiency attenuated the activation of the STAT3 pathway and VEGF production. Taken together, these data demonstrate that a loss of IL-6 causes cardiac dysfunction by shifting the cardiac cell populations, altering the extracellular matrix, and disrupting critical cell-cell interactions

Mnt Loss Triggers Myc Transcription Targets, Proliferation, Apoptosis, and Transformation

Myc oncoproteins are overexpressed in most cancers and are sufficient to accelerate cell proliferation and provoke transformation. However, in normal cells Myc also triggers apoptosis. All of the effects of Myc require its function as a transcription factor that dimerizes with Max. This complex induces genes containing CACGTG E-boxes, such as Ornithine decarboxylase (Odc), which harbors two of these elements. Here we report that in quiescent cells the Odc E-boxes are occupied by Max and Mnt, a putative Myc antagonist, and that this complex is displaced by Myc-Max complexes in proliferating cells. Knockdown of Mnt expression by stable retroviral RNA interference triggers many targets typical of the “Myc” response and provokes accelerated proliferation and apoptosis. Strikingly, these effects of Mnt knockdown are even manifest in cells lacking c-myc. Moreover, Mnt knockdown is sufficient to transform primary fibroblasts in conjunction with Ras. Therefore, Mnt behaves as a tumor suppressor. These findings support a model where Mnt represses Myc target genes and Myc functions as an oncogene by relieving Mnt-mediated repression