Coordinate changes in the expression of troponin subunit and myosin heavy‐chain isoforms during fast‐to‐slow transition of low‐frequency‐stimulated rabbit muscle

Abstract

The purpose of this study was to follow the time course of changes in the expression of myosin heavy chain (HC) and troponin (Tn) subunit isoforms during fast-to-slow transition as induced in rabbit fast-twitch muscle by low-frequency stimulation. The evaluation of changes in the relative concentrations of myosin and troponin subunit isoforms were supplemented by measurements of relative protein synthesis rates using an in situ labeling technique. Changes in the amounts of mRNA encoding fast troponin C (TnC) were followed by Northern blot analysis, those for fast and slow troponin I (TnI) by in vitro translation of total RNA. The various fast myosin heavy chain (HC) and fast troponin T (TnT) isoforms were exchanged sequentially. Myosin HCIId which is the predominant fast isoform in rabbit tibialis anterior, was exchanged with HCIIa and, finally, the latter was replaced by the slow myosin HCI. The replacement of HCIId by HCIIa was accompanied by an exchange of TnT,, and TnT,, with TnT,,. The expression of HCI was accompanied by an exchange of TnT,, with the slow TnT isoforms, TnT,, and TnT,,. The changes in the relative concentrations of the TnT isoforms were preceded by similar changes of their relative synthesis rates. Pronounced decreases in the fast TnI and TnC isoforms occurred only with prolonged stimulation and were preceded by changes of the specific mRNAs and decreases in relative synthesis rates. The parallel time courses of the sequential transitions in both the myosin heavy chain and troponin T isoforms suggest the existence of coordinate programs of expression serving specific functional requirements.Numerous studies have shown that mammalian fasttwitch muscles can be converted into slow-twitch muscles by low-frequency stimulation. The stimulation-induced transformation affects all elements of the muscle fiber studied to date (for review see [l, 21). At the level of the myofibrillar apparatus, chronic low-frequency stimulation induces fast-toslow transitions in the expression of thick and thin filament proteins. Studies on rabbit muscle showed changes in the myosin heavy chain pattern, such that long-term-stimulated fast-twitch muscles ultimately expressed the slow myosin heavy chain, HCI [3,4]. Time course studies including single fiber analyses on muscles of rat and rabbit revealed that the fast-to-slow fiber type transition was preceded by sequential exchanges of the various fast myosin heavy chain isoforms [4, 51. Fast-to-slow transitions were also observed for the three troponin (Tn) subunits, i.e., troponin T (TnT), troponin I (TnI), and troponin C (TnC). In the case of TnT, the changes consisted of sequential transitions in the expression of the major fast TnT isoforms, TnT,, TnTzh TnT,, and TnT,, Correspondence to D. Pette, Fakultat fur Biologie, UniversitatFax: +49 753188 39 40. Abbreviations. HC, heavy chain; Tn, troponin; TnC, troponin C; TnC,, fast troponin C; TnC,, slow troponin C ; TnI, troponin I; TnI,, fast troponin I; TnI,, slow troponin I; TnT, troponin T ; TnT,, TnT,, TnT3f, TnT,,,...

Proteomic profiling of chronic low‐frequency stimulated fast muscle

“…It is well established that the various light and heavy chains of myosin undergo a stepwise replacement from fast to slow isoforms during fibre type shifting [41,42], which has also been shown to occur in the case of regulatory elements of the contractile apparatus, such as the individual subunits of troponin [4]. The expanded views of 2-D landmark spots shown in Fig.…”

“…An elevation of aerobic-oxidative capacity, decreased fibre calibre and changes in the density of distinct muscle proteins, switches in isoform expression patterns and alterations in proteinprotein interactions are established biochemical and cell biological hallmarks of transformed skeletal muscles. This includes: (i) metabolic pathways such as the citric acid cycle, fatty acid oxidation and the respiratory chain which causes a drastic increase in enzymes of aerobic substrate oxidation [39,40], (ii) the contractile apparatus that undergoes a stepwise replacement of myosin light and heavy chains from fast isoforms to their slower counterparts [41,42], (iii) the ion-regulatory machinery of the excitation-contractionrelaxation cycle with a shift from fast to slower isoforms with respect to the SERCA-type Ca 21 -ATPases, the voltagesensing dihydropyridine receptor, the ryanodine receptor Ca 21 -release channel and various Ca 21 -binding proteins [43,44], (iv) the neuromuscular junction with distinct changes in the acetylcholinesterase and the nicotinic acetylcholine receptor [45,46] and, (v) a decrease in the supramolecular interaction pattern between Ca…”

Proximal Sequences of the Aldolase A Fast Muscle-specific Promoter Direct Nerve- and Activity-dependent Expression in Transgenic Mice

“…Moreover, adult muscle fibers are plastic entities whose phenotype can change and adapt in response to external influences including relative muscle usage, motor neuron activity, energy source availability, and hormonal status (4). The neuronal influence seems to be transmitted to skeletal muscle fibers mainly via contractile activity, and chronic low frequency electrical stimulation of muscle was shown to cause a transformation of fast fibers into slow fibers (5)(6)(7). These data suggest that nerve and muscle contractile activity play a major role in the final specialization of adult muscle fibers.…”

Myosin gene expression in the respiratory muscles

“…This transformation is not dependent on their substitution by new fibres, but on changes in the molecular expression of their MyHC isoforms [53]. As a general rule, the fast-type genes seem to be expressed "by default", whereas the slow-type genes would be expressed as a response to changes in loads [50][51][52]. Thus, a decrease in or lack of activity would result in a higher expression of fast MyHC, with an increase in the size and/or proportion of type I fibres [54][55][56][57][58].…”

“…The stretch (active tension) as well as electrical stimulation (passive tension) provoke the repression of the fast-type genes, with activation of the slow-type genes [2,48]. This implies a progressive transformation in the type of fibres [49][50][51][52]. This transformation is not dependent on their substitution by new fibres, but on changes in the molecular expression of their MyHC isoforms [53].…”