Ca2+-activated Protease Activity in Vitamin E-Deficient Rats

The mechanism and control of protein degradation in cells are quite mysterious. We investigated the change of protease activities in animals fed a vitamin E-deficient diet. The Ca²⁺-activated protease activity was not significantly changed in vitamin E-deficient rats during the 45 weeks of the experiment. The cathepsin B activity was increased in those animals. Electron microscopic observation on the muscle of the vitamin E-deficient rats showed destruction of myofibrils at the Z-line, narrowness of myofibrils, and dispersed myofibrils. The M-line, which is known to disappear with cathepsin L treatment, was clearly observed. The phagocytosis of muscle cells by macrophages was also observed. These results show that the abnormal myofibril protein degradation in muscle tissue of vitamin E-deficient rats is not only due to the activation of macrophages and the increment of lysosomes in muscle cells, but also due to the protease which can destroy the myofibril at the Z-line. It may be a Ca²⁺-activated protease.     

Elevated levels of a calcium-activated muscle protease in rapidly atrophying muscles from vitamin E-deficient rabbits.

A Ca2+-activated proteolytic enzyme that partially degrades myofibrils was isolated from hind limb muscles of normal rabbits and rabbits undergoing rapid muscle atrophy as a result of vitamin E deficiency. Extractable Ca2+-activated protease activity was 3.6 times higher in muscle tissue from vitamin E-deficient rabbits than from muscle tissue of control rabbits. Ultrastructural studies of muscle from vitamin E-deficient rabbits showed that the Z disk was the first myofibrillar structure to show degradative changes in atrophying muscle. Myofibrils prepared from muscles from vitamin E-deficient rabbits showed partial or complete loss of Z-disk density. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the amount of troponin-T (37 000 daltons) and alpha-actinin (96 000 daltons) was reduced in myofibrils from atrophying muscle as compared to myofibrils prepared from control muscle. In vitro treatment of purified myofibrils with purified Ca2+-activated proteolytic enzyme produced alterations in myofibrillar ultrastructure that were identical to the initial alterations occurring in myofibrils from atrophying muscle (i.e. weakening and subsequent removal of Z disks). Additonally the electrophoretic banding pattern of Ca2+-activated proteolytic enzyme-treated myofibrils is very similar to that of myofibrils prepared from muscles atrophying as a result of nutritional vitamin E deficiency. The possible role of Ca2+-activated proteolytic enzyme in disassembly and degradation of the myofibril is discussed.     

Possible participation of cyclic AMP in regulating acid hydrolase activity in muscle tissue in avitaminosis E and denervation]

In the muscles of denervated and vitamin E-deficient rabbits the level of 3', 5'-cyclic AMP proved to decrease with a simultaneous increase in the activity of cAMP phosphodiesterase. In vivo experiments showed that at the concentration of 10(-4) cAMP was capable of retarding the release of acid phosphatase from the lysosome-rich fraction obtained from the muscles of E-deficient rabbits. Thus, in muscular dystrophy elevation of acid hydrolase activity in the skeletal muscle was due to leakage of the enzymes from the lysosomes as a result of decreased lysosome membrane stability because of decreased cAMP level.     

Cathepsin B, D and H activities in muscles of chicks of fast and slow growing strains: effect of age and diet

1. Activities of cathepsins B, D and H were measured in leg and breast muscles of fast growing (broiler) and slow growing (layer) chicks at eight time intervals between 1 and 29 days of age. 2. These enzyme activities were also measured in muscles from fast and slow growing chicks given a low protein (125 g/kg crude protein) diet between the ages of 17 and 24 days. 3. Activities of none of these cathepsins differed greatly between muscle type or strain of chick. However in both strains of chick cathepsin D and H in muscles significantly decreased with increasing age (muscle size) of the chick. Cathepsin D activity also increased when muscle proteolytic rates were increased by feeding a low protein diet. This latter effect was significant only in the muscles of fast growing chicks. 4. The results suggest that lysosomal proteases are not responsible for the differences in muscle protein degradation and growth between fast and slow growing strains of chicks, or between muscle types in the chick.     

Elevated levels of a calcium-activated muscle protease in rapidly atrophying muscles from vitamin E-deficient rabbits

A Ca²⁺-activated proteolytic enzyme ¹ that partially degrades myofibrials was isolated from hind limb muscles of normal rabbits and rabbits undergoing rapid muscle atrophy as a result of vitamin E deficiency. Extractable Ca²⁺-activated protease activity was 3.6 times higher in muscle tissue from vitamin E-deficient rabbits than from muscle tissue of control rabbits. Ultrastructural studies of muscle from vitamin E-deficient rabbits showed that the Z disk was the first myofibrillar structure to show degradative changes in atrophying muscle. Myofibris prepared from muscles vitamin E-deficient rabbits showed partial or complete loss of Z-disk density. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the amount of troponin-T (37 000 daltons) and α-actinin (96 000 daltons) was reduced in myofibrils from atrophying muscle as compared to myofibrils prepared from control muscle. In vitro treatment of purified myofibrils with purified Ca²⁺-activated proteolytic enzyme produced alterations in myofibrillar ultrastructure that were identical to the initial alterations occuring in myofibrils from atrophying muscle (i.e. weakening and subsequent removal of Z disks). Additionally the electrophoretic banding pattern of Ca²⁺-activated proteolytic enzyme-treated myofibrils is very similar to that of myofibrils prepared from muscles atrophying as a result of nutritional vitamin E deficiency. The possible role of Ca²⁺-activated proteolytic enzyme in disassembly and degradation of the myofibril is discussed.     

Vitamin E deficiency and vitamin C supplements: exercise and mitochondrial oxidation

The effects of dietary antioxidant vitamins E and C on exercise endurance capacity and mitochondrial oxidation were investigated in rats. The endurance capacity of both vitamin E-deficient and vitamin C-supplemented, E-deficient rats was significantly (P less than 0.05) lower (38.1 and 33.6%, respectively) than control animals. Compared with the normal and vitamin E-deficient rats, there was a significant (P less than 0.05) increase in the concentration of vitamin C in blood and liver of the vitamin E-deficient, C-supplemented animals. Hence dietary vitamin C supplementation does not prevent the inhibition of exercise endurance capacity or increased hemolysis seen in vitamin E deficiency. The mitochondrial activities for the oxidation of palmitoyl carnitine and alpha-ketoglutarate were significantly (P less than 0.05) decreased by a single bout of exercise in brown adipose tissue but not in muscle, heart, or liver from vitamin C-supplemented, E-deficient groups of rats when compared with the activities in the tissue from the same group of rats killed at rest. Similar results were also seen in brown adipose tissue from vitamin E-deficient rats. The results suggest a tissue-specific role for vitamins E and C in substrate oxidation and show that the poor endurance capacity of vitamin E-deficient rats cannot be attributed to any changes in the mitochondrial activity in skeletal or cardiac muscles. It is also concluded that vitamin C supplementation, at least at the dose employed in the present study, cannot counteract the detrimental effects associated with vitamin E deficiency.     

Abnormalities of lipid metabolism in the vitamin E-deficient monkey

A soybean protein diet was used to induce vitamin E deficiency in rhesus monkeys. The deficient monkeys had reduced triglyceride concentrations in liver and skeletal muscle, but the cholesterol concentration in their skeletal muscle was increased. A constant amount of radioactively labeled (3)H-cholesterol-7alpha-(3)H was fed daily for 48-114 days to control and vitamin E-deficient monkeys to study the relationship between plasma, liver, and skeletal muscle cholesterol. Plasma cholesterol reached constant, maximum specific activity by the 42nd day both in control and in vitamin E-deficient monkeys. In control and previously deficient vitamin E-treated monkeys the specific activity of cholesterol in liver and skeletal muscle was approximately equal to that of plasma. In vitamin E-deficient monkeys the liver cholesterol specific activity was equal to that of plasma cholesterol, but the ratio of skeletal muscle cholesterol specific activity to plasma cholesterol specific activity was reduced. It is concluded from these studies that there is a specific defect(s) in cholesterol metabolism in the skeletal muscle of vitamin E-deficient monkeys.     

Changes of gangliosides and other lipids in skeletal muscle from rabbits with experimental dystrophy

Comparison of the skeletal muscles from vitamin E-deficient and control rabbits showed that the muscles from the deficient animals had lower contents of protein and glycogen but more water and lipid. Increases of individual lipids per unit weight of muscle from deficient animals compared with those from control animals were 2.2-fold for gangliosides, 2.18-fold for cholesterol, 1.74-fold for sulfatides, and 1.45-fold for neutral glycosylceramides. Total phospholipids did not change; this was the result of an increase in sphingomyelin (1.47-fold) and a decrease of phosphatidylcholine to 83% of the control, while the other fractions remained unchanged. When the measurements were referred to total muscle, the contents of cholesterol, gangliosides, sulfatides, neutral glycosylceramides, and sphingomyelin in muscle from vitamin E-deficient rabbits were also above those of the control rabbits, and only the phosphatidylcholine content was decreased. It was not possible to determine whether the alteration of lipid content preceded or followed the onset of signs of muscular dystrophy.     

Reciprocal neural regulation of extrajunctional acetylcholinesterase and collagen Q in rat muscles--the role of calcineurin signaling

There are two main differences regarding acetylcholinesterase (AChE) expression in the extrajunctional regions of fast and slow rat muscles: (1) the activity of AChE catalytic subunits (G1 form) is much higher in fast than in slow muscles, and (2) the activity of the asymmetric forms of AChE (A(8) and A(12)) is quite high extrajunctionally in slow muscles but virtually absent in fast muscles. The latter is due to the absence of the expression of AChE-associated collagen Q (ColQ) in the extrajunctional regions of fast muscle fibers, in contrast to its ample expression in slow muscles. We showed that both differences are caused by different neural activation patterns of fast vs. slow muscle fibers, which determine the respective levels of mRNA of both proteins. Whereas the changes in AChE mRNA levels in fast and slow muscles, as well as the levels of ColQ mRNA levels in slow muscles, observed in response to exposing either slow or fast muscles to different muscle activation patterns, are completely reversible, the extrajunctional suppression of ColQ expression in fast muscle fibers seems to be irreversible. Calcineurin signaling pathway in muscles is activated by high-average sarcoplasmic calcium concentration resulting from tonic low-frequency muscle fiber activation pattern, typical for slow muscle fibers, but is inactive in fast muscle fibers, which are activated by infrequent high-frequency bursts of neural impulses. Application to rats of two inhibitors of calcineurin (tacrolimus-FK506 and cyclosporin A) demonstrated that the mRNA levels of both the AChE catalytic subunit and ColQ in the extrajunctional regions of the soleus muscle are regulated by the calcineurin signaling pathway, but in a reciprocal way. Under the conditions of low calcineurin activity, AChE expression is enhanced and that of ColQ is suppressed, and vice versa. Our results also indicated that different, calcineurin-independent regulatory pathways are responsible for the reduction of AChE expression during muscle denervation, and for maintaining high ColQ expression in the neuromuscular junctions of fast muscle fibers.     

Myogenic and neurogenic contributions to the development of fast and slow twitch muscles in rat.

The histochemical ATPase activity and the myosin light chains of a rat fast muscle (extensor digitorum longus, EDL) and a rat slow muscle (soleus) during development have been investigated. Both muscles initially synthesize fast myosin light chains and show the intense histochemical ATPase activity characteristic of adult fast muscle fibers. After birth, the soleus begins to accumulate slow fibers with their characteristic low histochemical ATPase activity, and slow myosin light chains begin to appear. Sciatic neurectomy prevents the development of slow fibers and the synthesis of slow myosin light chains in the soleus, while the EDL is unaffected. Similarly, cordotomy of an adult rat results, in the soleus, in the appearance of fibers with more intense staining for ATPase and an increase in fast myosin light chains. The EDL is unchanged by cordotomy. As a result, we suggest that slow muscle development, but not fast muscle development, is dependent upon the functional activity of the nervous system.     

Reciprocal neural regulation of extrajunctional acetylcholinesterase and collagen Q in rat muscles—The role of calcineurin signaling

There are two main differences regarding acetylcholinesterase (AChE) expression in the extrajunctional regions of fast and slow rat muscles: (1) the activity of AChE catalytic subunits (G1 form) is much higher in fast than in slow muscles, and (2) the activity of the asymmetric forms of AChE (A₈ and A₁₂) is quite high extrajunctionally in slow muscles but virtually absent in fast muscles. The latter is due to the absence of the expression of AChE-associated collagen Q (ColQ) in the extrajunctional regions of fast muscle fibers, in contrast to its ample expression in slow muscles. We showed that both differences are caused by different neural activation patterns of fast vs. slow muscle fibers, which determine the respective levels of mRNA of both proteins. Whereas the changes in AChE mRNA levels in fast and slow muscles, as well as the levels of ColQ mRNA levels in slow muscles, observed in response to exposing either slow or fast muscles to different muscle activation patterns, are completely reversible, the extrajunctional suppression of ColQ expression in fast muscle fibers seems to be irreversible. Calcineurin signaling pathway in muscles is activated by high-average sarcoplasmic calcium concentration resulting from tonic low-frequency muscle fiber activation pattern, typical for slow muscle fibers, but is inactive in fast muscle fibers, which are activated by infrequent high-frequency bursts of neural impulses. Application to rats of two inhibitors of calcineurin (tacrolimus-FK506 and cyclosporin A) demonstrated that the mRNA levels of both the AChE catalytic subunit and ColQ in the extrajunctional regions of the soleus muscle are regulated by the calcineurin signaling pathway, but in a reciprocal way. Under the conditions of low calcineurin activity, AChE expression is enhanced and that of ColQ is suppressed, and vice versa. Our results also indicated that different, calcineurin-independent regulatory pathways are responsible for the reduction of AChE expression during muscle denervation, and for maintaining high ColQ expression in the neuromuscular junctions of fast muscle fibers.     

Early biochemical consequences of denervation in fast and slow skeletal muscles and their relationship to neural control over muscle differentiation

1. One week after denervation several biochemical characteristics of the fast extensor digitorum longus and slow soleus muscles from adult rats were investigated and compared with the characteristics of the corresponding unoperated contralateral muscles. 2. After these short periods of denervation-induced atrophy, the isolated myosins showed unchanged ATPase (adenosine triphosphatase) activities, but there was the expected difference between fast and slow muscle. 3. The specific activities of several soluble enzymes and their characteristic patterns were found to be only slightly modified in both the extensor and soleus muscles after denervation, as were most of the activities measured in the isolated mitochondria. 4. The most significant modifications were in the isolated sarcoplasmic reticulum, and appeared to be specific to either slow or fast muscle. 5. Denervation of slow muscle led to a marked increase of Ca(2+)-transport rates, and of the specific activity of the Mg(2+)-activated K(+)-modulated Ca(2+)-stimulated ATPase, together with changes in the polyacrylamide-electrophoretic profiles of the microsomal membrane protein. Transformation of these several properties of slow muscle sarcoplasmic reticulum to those of fast muscle sarcoplasmic reticulum was further substantiated by electron-microscopic analysis after negative staining. Control experiments with tenotomized soleus muscle gave negative results. 6. The isolated sarcoplasmic reticulum from fast muscle showed a slight diminution of ATPase-linked Ca(2+)-transport activity and a selective increase of rotenone-insensitive NADH-cytochrome c reductase activity, in addition to a greater emphasis on slow-type electrophoretic components of the structural membrane protein. 7. The significance of these results in relation to specific differentiating influences from motor nerves is discussed.     

Neural regulation of mammalian fast and slow muscle myosins: an electrophoretic analysis.

Mammalian nerves to fast and slow muscles have the remarkable property of changing the speed of contraction of muscles following cross-reinnervation. The biochemical basis of speed transformation is the change in myosin in ATPase activity. This paper provides electrophoretic evidence for structural changes in myosin from cross-reinnervated muscles. A method is described for the separation of intact fast and slow muscle myosins by polyacrylamide gel electrophoresis. This method utilizes the fact that ATP and its analogs prevent the formation of myosin polymers in low ionic strength buffers. In this system, normal fast muscle myosin has a higher electrophoretic mobility than slow muscle myosin. Normal rat soleus myosin has a major slow and a minor fast component due to two populations of muscle fibers. The same muscle cross-reinnervated by a fast muscle nerve shows only the fast component, The normal, homogeneous fast extensor digitorum longus muscle has only the electrophoretically fast myosin, but following cross-reinnervation it shows both fast and slow components. These results suggest that mammalian motor nerves can induce or suppress the expression of genes that code for fast and slow skeletal muscle myosins.     

Acetylcholinesterase in singly and multiply innervated muscles of normal and dystrophic chickens. II. Effects of denervation.

Neural regulation of mature normal fast twitch muscle of the chicken suppresses high activity, extrajunctional localization, and isozyme forms of acetylcholinesterase (AChE) characteristic of embryonic, denervated and dystrophic muscle. Normal adult slow tonic muscle ofthe chicken retains intermediate levels of activity and embryonic isozyme forms but not extrajunctional activity; it is not affected by muscular dystrophy. The hypothesis that neural regulation of the AChE system is lacking in slow tonic muscle and thus not affected by dystrophy was tested by denervating the fast twitch posterior latissimus dorsi and slow tonic anterior latissimus dorsi muscles of normal and dystrophic chickens. Extrajunctional AChE activity and embryonic isozyme forms increased, then declined, in both muscles. The results suggest that ocntrol of AChE is qualitatively similar in slow tonic and fast twitch muscle of the chicken.     

Properties of ryanodine receptor in rat muscles submitted to unloaded conditions

Unloading of skeletal muscles by hindlimb unweighting is known to induce muscle atrophy and a shift toward faster contractile properties associated with an increase in the expression of fast contractile proteins, particularly in slow soleus muscles. Contractile properties suggest that slow soleus muscles acquire SR properties close to those of a faster one. We studied the expression and properties of the sarcoplasmic reticulum calcium release (RyR) channels in soleus and gastrocnemius muscles of rats submitted to hindlimb unloading (HU). An increase in RyR1 and a slight decrease in RyR3 expression was detected in atrophied soleus muscles only after 4 weeks of HU. No variation appeared in fast muscles. [(3)H]Ryanodine binding experiments showed that HU neither increased the affinity of the receptors for [(3)H]ryanodine nor changed the caffeine sensitivity of [(3)H]ryanodine binding. Our results suggested that not only RyR1 but also RyR3 expression can be regulated by muscle activity and innervation in soleus muscle. The changes in the RyR expression in slow fibers suggested a transformation of the SR from a slow to a fast phenotype.     

Interaction of vitamin E and exercise training on oxidative stress and antioxidant enzyme activities in rat skeletal muscles

It has been shown that free radicals are increased during intensive exercise. We hypothesized that vitamin E (vit E) deficiency, which will increase oxidative stress, would augment the training-induced adaptation of antioxidant enzymes. This study investigated the interaction effect of vit E and exercise training on oxidative stress markers and activities of antioxidant enzymes in red quadriceps and white gastrocnemius of rats in a 2x2 design. Thirty-two male rats were divided into trained vit E-adequate, trained vit E-deficient, untrained vit E-adequate, and untrained vit E-deficient groups. The two trained groups swam 6 h/day, 6 days/week for 8 weeks. The two vit E-deficient groups consumed vit E-free diet for 8 weeks. Vitamin E-training interaction effect was significant on thiobarbituric acid reactive substances (TBARSs), glutathione peroxidase (GPX), and superoxide dismutase (SOD) in both muscles. The trained vit E-deficient group showed the highest TBARS and GPX activity and the lowest SOD activity in both muscles. A significant vit E effect on glutathione reductase and catalase was present in both muscles. Glutathione reductase and catalase activities were significantly lower in the two vit E-adequate groups combined than in the two vit E-deficient groups combined in both muscles. This study shows that vit E status and exercise training have interactive effect on oxidative stress and GPX and SOD activities in rat skeletal muscles. Vitamin E deprivation augmented the exercise-induced elevation in GPX activity while inhibiting exercise-induced SOD activity, possibly through elevated oxidative stress.     

The relation between ATPASE activity and light chains of myosin in developing, adult and denervated muscles of several animals species.

Ca2+ATPase activity and light chains of myosin, fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in developing, adult and denervated fast, slow and cardiac muscles of the rat, guinea-pig, cat, rabbit and chick were studied. It has been shown that in normal adult muscles the electrophoretic pattern of light chains of myosin reflects the myosin ATPase activity only when muscles from the same animal species are compared. In homologous muscles from adult animals differing in size, the size-dependent difference in myosin ATPase activity is not revealed in the electrophoretic pattern. Both in developing and in denervated muscle, changes in myosin ATPase activity are either connected with changes in the pattern of light chains of myosin or this pattern does not change. This relation is different in fast and slow muscles and also differs in chick and rabbit muscles. There are several possibilities of explaining the relation between ATPase activity of myosin and the pattern of light chains of myosin. The observation that myosin from the soleus muscle of 1-month-old rabbit contains light chains corresponding to both fast and slow type of myosin, indicates that the change in myosin ATPase activity during development is due to changes in the ratio between the fast and slow type of myosin.     

Denervation and reinnervation of fast and slow muscles. A histochemical study in rats.

A histochemical study, using myosin-adenosine triphosphatase activity at pH 9.4, was conducted in soleus and plantaris muscles of adult rats, after bilateral crushing of the sciatic nerve at the sciatic notch. The changes in fiber diameter and per cent composition of type I and type II fibers plus muscle weights were evaluated along the course of denervation-reinnervation curve at 1, 2, 3, 4 and 6 weeks postnerve crush. The study revealed that in the early denervation phase (up to 2 weeks postcrush) both the slow and fast muscles, soleus and plantaris, resepctively, atrophied similarly in muscle mass. Soleus increased in the number of type II fibers, which may be attributed to "disuse" effect. During the same period, the type I fibers of soleus atrophied as much or slightly more than the type II fibers; whereas the type II fibers of plantaris atrophied significantly more than the type I fibers, reflecting that the process of denervation, in its early stages, may affect the two fiber types differentially in the slow and fast muscles. It was deduced that the type I fibers of plantaris may be essentially different in the slow (soleus) and fast (plantaris) muscles under study. The onset of reinnervation, as determined by the increase in muscle weight and fiber diameter of the major fiber type, occurred in soleus and plantaris at 2 and 3 weeks postcrush, respectively, which confirms the earlier hypotheses that the slow muscles are reinnervated sooner than the fast muscles. It is suggested that the reinnervation of muscle after crush injury may be specific to the muscle type or its predominant fiber type.     

Lysosomal enzyme activities in muscle following starvation and refeeding in the saithe Pollachius virens L

Saithe (Pollachius virens L.) were starved for 66 days at 10 degrees C and activities of aryl sulfatase, acid proteinase, beta-glucuronidase, RNAase and acid phosphatase measured in homogenates prepared from fast and slow myotomal muscles. In fed fish, hydrolase activities were generally higher in slow than fast muscles. With the exception of acid proteinase activity in slow muscle, the activities of all the lysosomal enzymes increased by 70 to 100% during starvation. In general, there was a proportionally larger increase in the hydrolase activities in fast than in slow muscle. In a second experiment, fish were starved for 74 days, and refed for up to 52 days. The increases in aryl sulfatase and acid proteinase activity produced in fast muscle with starvation were found to be rapidly reversed by refeeding. Lysosomal enzyme activities in fish sampled after 10 days refeeding were not significantly different from fed controls. Membrane fractions enriched in aryl sulfatase activity were prepared from the fast muscle of 66-day starved fish. These were capable of degrading both myosin heavy chains and actin to lower molecular weight peptides at acid (pH 5.0), but not at neutral pH. The results suggest a role for lysosomal enzymes in the breakdown of myofibrillar proteins during starvation.     

Unlike effects of denervation on the rate of entry of inorganic phosphate into rat slow and fast muscles.

The increased inorganic phosphate flow, characteristic of denervated gastrocnemius muscle is shown to be present in additional denervated fast muscles, i.e. the plantaris, tibialis anterior and extensor digitorum longus muscles. The response of the soleus, a slow muscle, to denervation is biphasic. After an initial decrease of the phosphate flow at the end of the first postoperative day, there is a secondary rise which has the same general characteristics as the rise observed in fast muscles i.e. an exponential or hyperbolic increase to an asymptotic value reached after thirty days. The denervated fast and slow muscles are not converging to an intermediate metabolic pattern. The changes in phosphate flow induced by denervation are reversible in the soleus as well as in the gastrocnemius muscles.