Reorganized stores and impaired calcium handling in skeletal muscle of mice lacking calsequestrin‐1

Abstract

Calsequestrin (CS), the major Ca2+ -binding protein in the sarcoplasmic reticulum (SR), is thought to play a dual role in excitation-contraction coupling: buffering free Ca 2+ increasing SR capacity, and modulating the activity of the Ca 2+ release channels (RyRs). In this study, we generated and characterized the first murine model lacking the skeletal CS isoform (CS1). CS1-null mice are viable and fertile, even though skeletal muscles appear slightly atrophic compared to the control mice. No compensatory increase of the cardiac isoform CS2 is detectable in any type of skeletal muscle. CS1-null muscle fibres are characterized by structural and functional changes, which are much more evident in fast-twitch muscles (EDL) in which most fibres express only CS1, than in slow-twitch muscles (soleus), where CS2 is expressed in about 50% of the fibres. In isolated EDL muscle, force development is preserved, but characterized by prolonged time-to-peak and half-relaxation time, probably related to impaired calcium release from and re-uptake by the SR. Ca 2+ -imaging studies show that the amount of Ca 2+ released from the SR and the amplitude of the Ca 2+ transient are significantly reduced. The lack of CS1 also causes significant ultrastructural changes, which include: (i) striking proliferation of SR junctional domains; (ii) increased density of Ca 2+ -release channels (confirmed also by 3 H-ryanodine binding); (iii) decreased SR terminal cisternae volume; (iv) higher density of mitochondria. Taken together these results demonstrate that CS1 is essential for the normal development of the SR and its calcium release units and for the storage and release of appropriate amounts of SR Ca 2+ .

Triadin Binding to the C-Terminal Luminal Loop of the Ryanodine Receptor is Important for Skeletal Muscle Excitation–Contraction Coupling

“…The absence of an effect on depolarizationinduced Ca 2+ release in pan-triadin knockout mice could result from a multitude of different compensatory mechanisms commandeered to correct for the loss of a critical RyR1 regulatory protein. In fact, skeletal muscle function and EC coupling is also not markedly altered following knockout of the skeletal muscle isoform of calsequestrin (CSQ1; Paolini et al, 2007). Similarly, cardiac SR Ca 2+ storage and depolarization-induced Ca 2+ release are essentially normal following either global knockout of CSQ2 (Knollmann et al, 2006) or cardiac-specifi c knockout of the Na/Ca exchanger (Henderson et al, 2004), respectively.…”

Sequential stages in the age-dependent gradual formation and accumulation of tubular aggregates in fast twitch muscle fibers: SERCA and calsequestrin involvement

“…6b). The dots are clearly not composed of CASQ1, a protein that is totally absent in these fibers (Paolini et al 2007). The SR aggregates in CASQ1-null fibers seem to be a repetition of this structure in the sense that small dense dots are present inside each circular sectioned tubule profile and that the size of the circles is similar to the scallops in the jSR.…”

Aerobic Training Prevents Heat-Strokes in Calsequestrin 1 Knockout Mice by Reducing Oxidative Stress

“…Significant differences were observed for the functional output, as the grip strength test revealed that untrained CASQ1-null mice were about 60% weaker than age-matched WT at both 2 and 4 months of age. On the other hand, the maximum speed reached during the incremental test was surprisingly higher in CASQ1-null mice: this last result is likely due to the increased number and volume of mitochondria in CASQ1-null muscles (see below; see also [27]). Two months of aerobic training (2 to 4 months of age; see Figure 1), while did not change the average body weight of CASQ1-null mice, significantly improved both functional parameters: (a) the grip strength output normalized by weight increased from 3.0 ± 0.8 g/g of body weight in untrained CASQ1-null to 4.8 ± 1.1 g/g of body weight in trained CASQ1-null and (b) the maximum speed reached during the incremental test was slightly higher in trained than in untrained CASQ1-null mice, respectively, 32.5 ± 3.9 versus 28.1 ± 2.7 m/min.…”

“…CASQ1-null mice were generated as previously described [27]. All animals used in this study were males, as this gender is more susceptible to MH/ EHS-like crises when exposed to halothane and heat [22].…”

“…The molecular mechanisms underlying rhabdomyolysis of skeletal muscle fibers during MH/EHS crises appear to be complex cascade of events revolving around an increased leak of Ca 2+ from the mutated RyR1 [24][25][26][27][28] and an excessive production of reactive oxygen/nitrogen species (ROS/RNS) [24]. Michelucci et al [23] demonstrated that administration of antioxidants (N-acetylcysteine and trolox) protects CASQ1-null mice from anesthetic-and heat-induced lethal crises by reducing mitochondrial production of superoxide anion and global oxidative stress.…”