CSRP3 or Muscle LIM protein (MLP) is a nucleocytoplasmic shuttling protein and a mechanosensor in cardiac myocytes. MLP regulation and function was studied in cultured neonatal rat myocytes treated with pharmacological or mechanical stimuli. Either verapamil or BDM decreased nuclear MLP while phenylephrine and cyclic strain increased it. These results suggest that myocyte contractility regulates MLP subcellular localization. When RNA polymerase II was inhibited with α-amanitin, nuclear MLP was reduced by 30%. However, when both RNA polymerase I & II were inhibited with actinomycin D, there was a 90% decrease in nuclear MLP suggesting that its nuclear translocation is regulated by both nuclear and nucleolar transcriptional activity. Using cell permeable synthetic peptides containing the putative nuclear localization signal (NLS) of MLP, nuclear import of the protein in cultured rat neonatal myocytes was inhibited. The NLS of MLP also localizes to the nucleolus. Inhibition of nuclear translocation prevented the increased protein accumulation in response to phenylephrine. Furthermore, cyclic strain of myocytes after prior NLS treatment to remove nuclear MLP resulted in disarrayed sarcomeres. Increased protein synthesis and brain natriuretic peptide expression were also prevented suggesting that MLP is required for remodeling of the myofilaments and gene expression. These findings suggest that nucleocytoplasmic shuttling MLP plays an important role in the regulation of the myocyte remodeling and hypertrophy and is required for adaptation to hypertrophic stimuli.

Abstract-We report characterization of a transgenic mouse that overexpresses constitutively active protein kinase C⑀ in the heart and slowly develops a dilated cardiomyopathy with failure. The hemodynamic, mechanical, and biochemical properties of these hearts demonstrate a series of temporal events that mark the progression of the disease. In the 3-month transgenic (TG) animals, contractile properties and gene expression measurements are normal, but an increase in myofibrillar Ca 2ϩ sensitivity and thin filament protein phosphorylation is noted. At 6 months, there is a decrease in the myofibrillar Ca 2ϩ sensitivity, a significant increase in ␤-myosin heavy chain mRNA and protein, normal cardiac function, but a blunted response to an inotropic challenge. The transition at 9 months is especially interesting because age-related changes appear to contribute to the decline in function seen in the TG heart. At this point, there is a decline in baseline function and maximum tension produced by the myofibrils, which is coincident with the onset of atrial myosin light chain isoform re-expression in the ventricles. In the 12-month TG mice, there is clear hemodynamic and geometric evidence of failure. Alterations in the composition of the myofibrils persist but the phosphorylation of myosin light chain 2v is dramatically different at this age compared with all others. We interpret these data to implicate the disruption of the myofibrillar proteins and their interactions in the propagation of dilated cardiac disease. (Circ Res. 2004;95:424-432.)Key Words: contractile proteins Ⅲ heart failure Ⅲ protein kinase C H eart disease is the most frequent cause of death in the general population, with a dramatically increasing incidence in the elderly. 1 As with the aging heart, many pathologic features of heart failure are related to structural and functional alterations in cardiac muscle cells. However, the molecular mechanisms underlying the progression of heart failure at the level of cardiac muscle function are largely unknown.A number of diverse lines of evidence have suggested that activation of protein kinase C (PKC) plays a central role in the physiologic and pathophysiologic adaptation of the heart. Studies in vitro and in vivo have shown that PKC phosphorylates a number of important cardiac proteins, including myofilament proteins, 2 as well as proteins involved in Ca 2ϩ homeostasis. 3 Clearly, one hypothesis concerning PKC activation is that increased myofilament phosphorylation results in contractile dysfunction, which diminishes cardiac output, which results in a compensatory enlargement of the heart. This is supported by evidence showing that PKC-mediated phosphorylation of the myofilaments is associated with depressed myofilament activity in reconstituted systems. 4 Multiple isoforms of PKC are expressed in the heart during development, with the predominant isoforms in the adult being the Ca 2ϩ -dependent (␣) and the Ca 2ϩ -independent (␦, ⑀) isoforms. 5 Protein kinase C⑀, an isoform that translocates to the myofi...

The cytokine interferon-gamma (IFN-γ), is the only known member of the type II family of interferons, and as such, binds to its own distinct receptor. It is important in host defense against infection, as well as adaptive immune responses. Whilst a wide array of cytokines are known to be involved in adverse remodeling of the heart and the progression to heart failure, the role of IFN-γ is unclear. Recent evidence from clinical studies, animal models of myocarditis and hypertension, as well as isolated cell studies, provide conflicting data as to whether IFN-γ is pathological or protective in the heart. Thus, it is important to highlight these discrepant findings so that areas of future investigation can be identified to more clearly determine the precise role of IFN-γ in the heart. Accordingly, this review will: 1) discuss the source of IFN-γ in the diseased heart; 2) summarize the data from animal studies; 3) discuss the effects of IFN-γ on isolated cardiac fibroblasts and cardiomyocytes; 4) identify signaling mechanisms that may be invoked by IFN-γ in the heart; and 5) present the clinical evidence supporting a role for IFN-γ in heart failure.

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Myocardial infarction (MI) is a major cause of heart failure (HF) with the progressive worsening of cardiac performance due to structural and functional alterations. Therefore, we studied cardiac function in adult mice following MI using the Millar pressure-volume (P-V) conductance catheter system in vivo during the later phase of compensatory remodeling and decompensation to HF. We evaluated load-dependent and -independent parameters in control and 2-, 4-, 6-, and 10-wk post-MI mice and integrated changes in function with changes in gene expression. Our results indicated a significant deterioration of cardiac function in post-MI mice over time, reflected first by systolic dysfunction, followed by a transient improvement before further decline in both systolic and diastolic function. Associated with the function and adaptive remodeling were transient changes in fetal gene and extracellular matrix gene expression. However, undermining the compensatory remodeling response was a continual decline in cardiac contractility, which promoted the transition into failure. Our study provided a scheme of integrated cardiac function and gene expression changes occurring during the adaptive and maladaptive response of the heart independent of systemic vascular properties during the transition to HF following MI in mice. P-V loop analysis was used to quantitatively evaluate the gradual deterioration in cardiac function post-MI. P-V loop analysis was found to be an appropriate method for assessment of global cardiac function under varying load-dependent and -independent conditions in the murine model with many similarities to data obtained from larger animals and humans.

The assembly of sarcomeric proteins into the highly organized structure of the sarcomere is an ordered and complex process involving an array of structural and associated proteins. The sarcomere has shown itself to be considerably more complex than ever envisaged and may be considered one of the most complex macromolecular assemblies in biology. Studies over the last decade have helped to put a new face on the sarcomere, and, as such, the sarcomere is being redefined as a dynamic network of proteins capable of generating force and signalling with other cellular compartments and metabolic enzymes capable of controlling many facets of striated myocyte biology.