Mechanical stretch-induced activation of ROS/RNS signaling in striated muscle

Abstract

Significance: Mechanical activation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) occurs in striated muscle and affects Ca(2+) signaling and contractile function. ROS/RNS signaling is tightly controlled, spatially compartmentalized, and source specific.

Recent advances: Here, we review the evidence that within the contracting myocyte, the trans-membrane protein NADPH oxidase 2 (Nox2) is the primary source of ROS generated during contraction. We also review a newly characterized signaling cascade in cardiac and skeletal muscle in which the microtubule network acts as a mechanotransduction element that activates Nox2-dependent ROS generation during mechanical stretch, a pathway termed X-ROS signaling.

Critical issues: In the heart, X-ROS acts locally and affects the sarcoplasmic reticulum (SR) Ca(2+) release channels (ryanodine receptors) and tunes Ca(2+) signaling during physiological behavior, but excessive X-ROS can promote Ca(2+)-dependent arrhythmias in pathology. In skeletal muscle, X-ROS sensitizes Ca(2+)-permeable sarcolemmal "transient receptor potential" channels, a pathway that is critical for sustaining SR load during repetitive contractions, but when in excess, it is maladaptive in diseases such as Duchenne Musclar dystrophy.

Future directions: New advances in ROS/RNS detection as well as molecular manipulation of signaling pathways will provide critical new mechanistic insights into the details of X-ROS signaling. These efforts will undoubtedly reveal new avenues for therapeutic intervention in the numerous diseases of striated muscle in which altered mechanoactivation of ROS/RNS production has been identified.

FIG. 1.

Schematic representation of RNS and ROS production on the striated myocyte. See main text for details. ROS, reactive oxygen species; RNS, reactive nitrogen species; PLA2, phospholipase A2; TRP, transient receptor potential; RyR, ryanodine receptor; DHPR, dihydropyridine receptor; SOD, superoxide dismutase; XO, xanthine oxidase; jSR, junctional sarcoplasmic reticulum; t-tubule, transverse tubule; nNOS, neuronal nitric oxide synthase; NO, nitric oxide; ONOO⁻, peroxynitrite; Nox2, NADPH oxidase 2. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars

FIG. 2.

Time course of Fluo-4 signal intensity in a ventricular cardiomyocyte subjected to a half-cell stretch. The back panel shows an image of a cell, averaged from 10 confocal XY scans before the application of stretch. The low intensity areas indicate points of CF attachment at resting length (scale bar=20 μm). The front panel represents a pseudo color, pseudo 3D rendering of XT images temporally from back to front. Note that the shading across the image and the CF's fluorescence troughs indicate the stretch of one-half of the cell (right half) and that Ca²⁺ spark signals arise only in the stretched portion of the cell. This figure was used with permission from Iribe et al. (30). CF, carbon filament. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars

FIG. 3.

Kinetic response of the ROS signal generated during a brief cardiomyocyte stretch. Data are stylized based on experiments of a single cardiomyocyte loaded with the ROS indicator DCF and subjected to an 8% sarcomere length excursion (black trace) (57). DCF fluorescence intensity (blue trace) rises rapidly on the initiation of stretch and terminates rapidly with the relaxation of the stretch. The new level of DCF fluorescence after stretch reflects DCF as a non-reversible ROS indicator. The rate of ROS production estimated by the first derivative of the DCF fluorescence profile (green trace) indicates a burst of ROS production at the initiation of stretch that decays monotonically until relaxation. DCF, dichlorofluorescein. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars

FIG. 4.

Graphical representation of the X-ROS activation in striated muscle. The stress of mechanical stretch is transmitted through the filamentous microtubule network to Nox2, which generates superoxide and secondary ROS species (see review). We have demonstrated that the downstream targets of Nox2-derived ROS (i.e., X-ROS) result in sensitization of RyR's in heart and TRP channels in skeletal muscle. Other potential targets include CaMKII (76). CaMKII, calmodulin kinase II. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars