Monocytes and macrophages are important components of the immune system, specialized in either removing pathogens as part of innate immunity or contributing to adaptive immunity through antigen presentation. Essential to such functions is classical activation (M1) and alternative activation (M2) of macrophages. M1 polarization of macrophages is characterized by production of pro-inflammatory cytokines, antimicrobial and tumoricidal activity, whereas M2 polarization of macrophages is linked to immunosuppression, tumorigenesis, wound repair and elimination of parasites. MiRNAs are small non-coding RNAs with the ability to regulate gene expression and network of cellular processes. A number of studies have determined miRNA expression profiles in M1 and M2 polarized human and murine macrophages using microarray and RT-qPCR arrays techniques. More specifically, miR-9, miR-127, miR-155 and miR-125b have been shown to promote M1 polarization while miR-124, miR-223, miR-34a, let-7c, miR-132, miR-146a and miR-125a-5p induce M2 polarization in macrophages by targeting various transcription factors and adaptor proteins. Further, M1 and M2 phenotypes play distinctive roles in cell growth and progression of inflammation-related diseases such as sepsis, obesity, cancer and multiple sclerosis. Hence, miRNAs that modulate macrophage polarization may have therapeutic potential in the treatment of inflammation-related diseases. This review highlights recent findings in miRNA expression profiles in polarized macrophages from murine and human sources, and summarizes how these miRNAs regulate macrophage polarization. Lastly, therapeutic potential of miRNAs in inflammation-related diseases through modulation of macrophage polarization is also discussed.

Inhibiting FN polymerization or cardiac fibroblast gene expression attenuates pathological properties of MFs in vitro and ameliorates adverse cardiac remodeling and fibrosis in an in vivo model of heart failure. Interfering with FN polymerization may be a new therapeutic strategy for treating cardiac fibrosis and heart failure.

No abstract

Rationale: Mitochondrial Ca 2+ loading augments oxidative metabolism to match functional demands during times of increased work or injury. However, mitochondrial Ca 2+ overload also directly causes mitochondrial rupture and cardiomyocyte death during ischemia-reperfusion injury by inducing mitochondrial permeability transition pore opening. The MCU (mitochondrial Ca 2+ uniporter) mediates mitochondrial Ca 2+ influx, and its activity is modulated by partner proteins in its molecular complex, including the MCUb subunit. Objective: Here, we sought to examine the function of the MCUb subunit of the MCU-complex in regulating mitochondria Ca 2+ influx dynamics, acute cardiac injury, and long-term adaptation after ischemic injury. Methods and Results: Cardiomyocyte-specific MCUb overexpressing transgenic mice and Mcub gene-deleted ( Mcub − /− ) mice were generated to dissect the molecular function of this protein in the heart. We observed that MCUb protein is undetectable in the adult mouse heart at baseline, but mRNA and protein are induced after ischemia-reperfusion injury. MCUb overexpressing mice demonstrated inhibited mitochondrial Ca 2+ uptake in cardiomyocytes and partial protection from ischemia-reperfusion injury by reducing mitochondrial permeability transition pore opening. Antithetically, deletion of the Mcub gene exacerbated pathological cardiac remodeling and infarct expansion after ischemic injury in association with greater mitochondrial Ca 2+ uptake. Furthermore, hindlimb remote ischemic preconditioning induced MCUb expression in the heart, which was associated with decreased mitochondrial Ca 2+ uptake, collectively suggesting that induction of MCUb protein in the heart is protective. Similarly, mouse embryonic fibroblasts from Mcub −/− mice were more sensitive to Ca 2+ overload. Conclusions: Our studies suggest that Mcub is a protective cardiac inducible gene that reduces mitochondrial Ca 2+ influx and permeability transition pore opening after ischemic injury to reduce ongoing pathological remodeling.

Skeletal muscle can repair and regenerate due to resident stem cells known as satellite cells. The muscular dystrophies are progressive muscle wasting diseases underscored by chronic muscle damage that is continually repaired by satellite cell-driven regeneration. Here we generate a genetic strategy to mediate satellite cell ablation in dystrophic mouse models to investigate how satellite cells impact disease trajectory. Unexpectedly, we observe that depletion of satellite cells reduces dystrophic disease features, with improved histopathology, enhanced sarcolemmal stability and augmented muscle performance. Mechanistically, we demonstrate that satellite cells initiate expression of the myogenic transcription factor MyoD, which then induces re-expression of fetal genes in the myofibers that destabilize the sarcolemma. Indeed, MyoD re-expression in wildtype adult skeletal muscle reduces membrane stability and promotes histopathology, while MyoD inhibition in a mouse model of muscular dystrophy improved membrane stability. Taken together these observations suggest that satellite cell activation and the fetal gene program is maladaptive in chronic dystrophic skeletal muscle.

RationaleCardiomyocytes and fibroblasts in the heart communicate through both secreted growth factors as well as through sensing the structural properties of the extracellular matrix that each helps generate. Previous studies have shown that defects in fibroblast activity during disease stimulation result in altered cardiomyocyte hypertrophy, although the role that collagen might play in this communication is unknown.ObjectiveHere we investigated how type I collagen maturation and disease-responsive matrix expansion in the heart by cardiac fibroblasts impacts cardiac fibrosis and cardiomyocyte hypertrophy.Methods and ResultsWe generated and characterized Col1a2-/- mice using standard gene-targeting. Col1a2-/- mice were viable, although by young adulthood their hearts showed alterations in extracellular matrix mechanical properties, as well as an unanticipated activation of cardiac fibroblasts and induction of a progressive fibrotic response. This included increases in fibroblast number and a progressive cardiac hypertrophy, with reduced functional performance by 9 months. Col1a2-loxP targeted mice were also generated and crossed with the tamoxifen-inducible Postn-MerCreMer knock-in mice to delete the Col1a2 gene in myofibroblasts post-pressure overload injury, to more specifically implicate fibroblasts as effectors of cardiomyocyte hypertrophy in vivo. Opposite to the gradual induction of cardiac hypertrophy observed in germline Col1a2-/- mice as they matured developmentally, adult fibroblast-specific deletion of Col1a2 during pressure overload protected these mice from cardiac hypertrophy in the first week with a delayed fibrotic response. However, this reduction in hypertrophy due to myofibroblast-specific Col1a2 deletion was gradually lost over 2 and 6 weeks of pressure overload as augmented fibrosis returned.ConclusionsDefective type I collagen in the developing heart alters the structural integrity of the extracellular matrix that leads to fibroblast expansion, activation, fibrosis and hypertrophy with progressive cardiomyopathy in adulthood. However, acute deletion of type I collagen production for the first time in the adult heart during pressure overload prevents ECM expansion and inhibits cardiomyocyte hypertrophy, while gradual restoration of fibrosis again permitted hypertrophy comparable to controls.

Introduction: The ribosomal protein L3-like (RPL3L) is a heart and skeletal muscle-specific ribosomal protein and paralogue of the more ubiquitously expressed RPL3 protein. Mutations in the human RPL3L gene are linked to childhood cardiomyopathy and age-related atrial fibrillation, yet the function of RPL3L in the mammalian heart remains unknown.Methods and Results: Here, we observed that mouse cardiac ventricles express RPL3 at birth, where it is gradually replaced by RPL3L in adulthood but re-expressed with induction of hypertrophy in adults. Rpl3l gene-deleted mice were generated to examine the role of this gene in the heart, although Rpl3l−/− mice showed no overt changes in cardiac structure or function at baseline or after pressure overload hypertrophy, likely because RPL3 expression was upregulated and maintained in adulthood. mRNA expression analysis and ribosome profiling failed to show differences between the hearts of Rpl3l null and wild type mice in adulthood. Moreover, ribosomes lacking RPL3L showed no differences in localization within cardiomyocytes compared to wild type controls, nor was there an alteration in cardiac tissue ultrastructure or mitochondrial function in adult Rpl3l−/− mice. Similarly, overexpression of either RPL3 or RPL3L with adeno-associated virus −9 in the hearts of mice did not cause discernable pathology. However, by 18 months of age Rpl3l−/− null mice had significantly smaller hearts compared to wild type littermates.Conclusion: Thus, deletion of Rpl3l forces maintenance of RPL3 expression within the heart that appears to fully compensate for the loss of RPL3L, although older Rpl3l−/− mice showed a mild but significant reduction in heart weight.

Mitochondrial calcium alterations can promote oxidative metabolism to match increasing functional demands during stress stimulation. However, mitochondrial calcium overload-induced cell death contributes to the pathogenesis of several cardiac disorders including ischemia reperfusion injury. The mitochondrial calcium uniporter (MCU) complex is the only identified transporter that permits rapid calcium uptake into mitochondria. While the biological function of the MCU pore-forming subunit has been annotated, much less is known about the MCUb protein, a high similarity paralog that is part of the greater MCU complex. The goal of our study was to investigate the biological function of MCUb, its role in mitochondrial calcium uptake, and its contribution to the pathogenesis of ischemia reperfusion injury in the heart. To address these questions, we generated both MCUb overexpressing mice as well as MCUb null mice. We observed that the cardiac-specific overexpression of MCUb inhibited mitochondrial calcium uptake, although basal mitochondrial calcium levels remained unchanged. Genetic ablation of MCUb, conversely, did not influence mitochondrial calcium uptake in the heart. MCUb null mice did not have differences in cardiac function by echocardiography, nor were tissue histological changes observed. This lack of an overt phenotype in MCUb null mice may be attributable to very low or even absent expression in the heart at baseline. However, induction of MCUb protein was observed in the hearts of mice subjected to ischemia reperfusion injury. Thus, mice were challenged with one-hour ischemia followed by 24-hour reperfusion and the ischemic area/area at risk was analyzed. Deletion of MCUb did not change the initial infarct size of the heart. However, MCUb null mice showed decreased fractional shortening 4-weeks after the ischemic injury. Gravimetric analysis as well as histological examination further supported the conclusion that MCUb deletion exacerbated damage in the heart after ischemia reperfusion injury. We are currently investigating the underlying mechanisms of this greater functional deficit.