484 Endocrine Research

Aerobic Training Prevents Dexamethasone-Induced Peripheral Insulin Resistance

Affiliations

Key words

▶ glucocorticoids ● ▶ insulin cascade pathway ● ▶ aerobic exercise training ● ▶ skeletal muscle ●

T. J. Dionísio1, 2, J. C. A. Louzada3, B. A. Viscelli3, E. J. Dionísio3, A. M. Martuscelli3, M. Barel3, O. A. B. Perez3, J. R. Bosqueiro3, D. T. Brozoski2, C. F. Santos2, S. L. Amaral1, 3 1

Department of Physiological Science, Federal University of São Carlos – UFSCAR, São Carlos, Brazil Department of Biological Sciences, Bauru School of Dentistry, University of São Paulo, USP, Bauru, Brazil 3 Department of Physical Education, UNESP – São Paulo State University, Bauru, Brazil 2

Abstract



This study investigated how proteins of the insulin signaling cascade could modulate insulin resistance after dexamethasone (Dexa) treatment and aerobic training. Rats were distributed into 4 groups: sedentary control (SC), sedentary + Dexa (SD), trained control (TC), and trained + Dexa (TD), and underwent aerobic training for 70 days or remained sedentary. Dexa was administered during the last 10 days (1 mg · kg − 1 per day i. p.). After 70 days, an intraperitoneal glucose tolerance test (ipGTT) was performed. Protein levels of IRS-1, AKT, and PKC-α in the tibialis anterior

Introduction

▼ received 05.11.2013 accepted 19.02.2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1370990 Published online: April 7, 2014 Horm Metab Res 2014; 46: 484–489 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0018-5043 Correspondence S. L. Amaral, PhD Department of Physical Education Science Faculty UNESP – São Paulo State University Bauru, SP Brazil Tel.: + 55/14/3103 6082 Fax: + 55/14/3103 6082 [email protected]

Dexamethasone (Dexa) is widely used to treat chronic inflammatory diseases and allergies. However, excessive amounts of glucocorticoids are known to induce peripheral insulin resistance by possibly impairing the insulin-signaling pathway in muscle [1], liver [2], and adipose tissues [1]. Previous studies have shown that insulin resistance induces hyperinsulinemia to normalize blood glucose levels in experimental animals. In accordance, we have recently demonstrated that 10 days of Dexa treatment caused hyperinsulinemia, hyperglycemia, and skeletal muscle glycogen storage reductions [3]. Skeletal muscles represent the predominant peripheral glucose storage site [4], and part of the glucose uptake is modulated by the regulation of the insulin-signaling pathway. More specifically, glucose transporter (GLUT-4) translocation to the membrane is initially mediated by insulin receptor substrate type 1 and/or 2 (IRS-1 and/or IRS-2) followed by phosphatidylinositol-3-kinase (PI3-K) and protein kinase B (or AKT) [5]. It has also been demonstrated that Dexa injections decrease the protein level of IRS-1 and

Dionísio TJ et al. Dexamethasone Side Effects and Exercise … Horm Metab Res 2014; 46: 484–489

(TA) muscle were identified using Western blots. Dexa treatment increased blood glucose and the area under the curve (AUC) of ipGTT. Training attenuated the hyperglycemia and the AUC induced by Dexa. Dexa reduced IRS-1 (− 16 %) and AKT (− 43 %) protein level with no changes in PKC-α levels. Moreover, these effects on IRS-1 and AKT protein level were prevented in trained animals. These results show for the first time that aerobic exercise prevented reductions of IRS-1 and AKT level induced by Dexa in the TA muscle, suggesting that aerobic exercise is a good strategy to prevent Dexa-induced peripheral insulin resistance.

IRS-2 [2, 6–8], AKT [1, 6, 7, 9], and GLUT-4 [10] as well as decrease GLUT-4 translocation to the membrane [11]. In particular, these changes in the insulin-signaling pathway cause insulin resistance, which is one of the primary side effects of chronic Dexa treatment. Furthermore, some authors have found increases in protein kinase C-α (PKC-α) after Dexa treatment in other tissues besides skeletal muscle [12]. There is paucity of data regarding the effects of Dexa on skeletal muscle PKC-α protein level and, importantly, it has been suggested that PKC-τ level may be directly related to GLUT-4 translocation [13]. On the other hand, aerobic exercise training is known to improve insulin action on glucose uptake [14–16]. However, the mechanisms underlying this effect remain unclear. Some studies have suggested that physical aerobic exercise enhances insulin sensitivity and whole glucose uptake by increasing the protein level of IRS-1, IRS-2 [17, 18], p-AKT [17–20] as well as increasing the activity and phosphorylation of some PKC isoforms [21, 22]. In contrast, Rose et al. [22] found no difference in PKC-α protein level and activity in skeletal muscle after acute aerobic exercise training.

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Authors

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Materials and Methods



Materials Dexamethasone phosphate (Decadron®) was acquired from Ache (Guarulhos, SP, Brazil). Sodium thiopental (Thiopentax®) was purchased from Cristália (Itapira, SP, Brazil). Human recombinant insulin (Biohulin®) was obtained from Biobrás (Montes Claros, MG, Brazil). SDS-PAGE and immunoblotting were performed using Bio-Rad systems (Hercules, CA, USA). All chemicals used for immunoblotting were purchased either from Sigma (St. Louis, MO, USA) or Bio-Rad (Hercules, CA, USA). Primary antibodies were anti-total IRS-1 (# 2390, rabbit polyclonal, Cell Signaling), anti-p-IRS-1 Ser 612 (# 2386, rabbit polyclonal, Cell Signaling), anti-total PKC-α (# 2056, rabbit polyclonal, Cell Signaling), anti-p-PKC-α (# 06822, rabbit polyclonal, Upstate), antip-AKT Ser 473 (# 9271, rabbit polyclonal, Cell Signaling), and anti-total AKT (# 9272, rabbit polyclonal, Cell Signaling). Secondary antibody was goat anti-Rabbit IgG (H + L)-HRP conjugated (# 170-6515, Bio-Rad, Hercules, CA, USA). The enhanced chemiluminescence substrate detection system (Super signal® West Pico) was purchased from Pierce (Rockford, IL, USA).

Animals Eighty inbred Wistar rats (ranging from 7 to 8 weeks of age, 200 g to 270 g) were obtained from the UNESP, São Paulo State University, Animal Care Unit, Campus of Botucatu. All animals were housed in group cages (5 animals each). These rats were given water and food (Laboratory Rodent Diet Purina) ad libitum and maintained on a 12-h light on (6 AM–6 PM) and 12-h light off (6 PM–6 AM) cycle in a temperature-controlled room (22 °C). Experiments were conducted during the day period. Rats were weighed weekly during the aerobic exercise protocol and daily during the treatment protocol. The Institutional Animal Care and Use Committee of the UNESP, São Paulo State University, approved all the surgical procedures and protocols used (# 1268/46/01/09).

Experimental groups After the evaluation of the physical capacity, the animals were weighed and distributed into 4 experimental groups, which followed a 70 day protocol. The 4 experimental groups were: sedentary control (SC), sedentary during all the periods, receiving daily vehicle (saline) i. p. injection during the last 10 days; sedentary Dexa (SD), sedentary during all the periods, receiving daily Dexa (1 mg · kg − 1, i. p., dissolved in saline) injections during the last 10 days; trained control (TC), 8 weeks of aerobic exercise training, receiving daily saline i. p. injections during the following 10 days (concomitantly with aerobic exercise training) and trained Dexa (TD), 8 weeks of aerobic exercise training, receiving daily Dexa (1 mg · kg − 1, i. p., dissolved in saline) injections during the following 10 days. This dose of Dexa (1 mg · kg − 1, daily) has been previously published by our group and collaborators [23, 24], and is an accepted method known to induce hepatic and extra hepatic insulin resistance. Dexa or saline was injected daily between 8 AM and 9 AM.

Aerobic exercise training protocol For 8 weeks excluding weekends, all rats were assigned to run on a treadmill at 60 % of their maximum speed reached at the first Tmax, 0 % grade, for 1 h per day. After 4 weeks of aerobic exercise training, a second Tmax was applied in order to maintain the same aerobic exercise intensity throughout the experimental protocol. At the end of 8 weeks of aerobic exercise training, a third Tmax was applied, just prior to the drug treatment protocol. A control group of sedentary rats also underwent their Tmax in parallel to the trained rats; however, in their case, they remained sedentary during the entire experimental protocol.

Determination of blood glucose Blood samples from the tails of fasted rats (12 h) were taken to measure blood glucose levels using a glucometer (One-touch Ultra, Johnsons and Johnsons®, New Brunswick, NJ, USA). Blood samples were taken at 2 time points: during the first day of Dexa administration, but before Dexa administration, and just prior to euthanasia, 30 h after the last aerobic exercise session.

Intraperitoneal glucose tolerance test (ipGTT) We performed an ipGTT in a separate group of animals. On the day following the last Dexa injection, each group of fasted (12 h) rats were anesthetized with sodium thiopental (60 mg · kg − 1 body mass, i. p.). After checking for the absence of the corneal and pedal reflexes, an unchallenged sample (time 0) was obtained from the tail. Immediately after, 50 % glucose (2 g · kg − 1 body mass, i. p.) was administered. Blood samples were collected at 30, 60, 90, and 120 min from the tail tip to determine glucose concentrations.

Western blotting procedures Evaluation of the maximal physical capacity Each animal underwent 5 familiarization periods on a treadmill prior the start of the testing protocol, and each familiarization period lasted about 3 min (0.3 km · h − 1 mild aerobic exercise, 0 % grade). The individual maximum capacity was evaluated through a progressive maximal test (Tmax) on a treadmill, following a previously validated protocol published by Silva et al. (1997) with increments of 5 m · min − 1 every 3 min, 0 % grade. The maximum capacity was determined when the animal stopped running spontaneously.

Immediately following decapitation, samples of TA muscle were homogenized and the proteins were suspended in potassium buffer (10 mM) with 0.1 mM phenylmethylsulfonyl fluoride (PMSF). As determined by a protein assay kit (Bio-Rad), 30 μg of muscle protein were separated on a 10–12 % denaturing polyacrylamide gel. These proteins were transferred from the gels to nitrocellulose membranes, which were blocked for 2 h at 22 °C in 5 % nonfat dry milk diluted in a solution (50 mM Tris and 750 mM NaCl; pH 5.8) with 1 % Tween 20 (Bio-Rad). These blots were then incubated overnight with either 1:1,000 anti-total and

Dionísio TJ et al. Dexamethasone Side Effects and Exercise … Horm Metab Res 2014; 46: 484–489

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Recently, studies from our laboratory have shown that aerobic exercise, performed before and during Dexa treatment, can prevent some of the side effects induced by this drug [3], including hyperglycemia. However, the intracellular mechanisms responsible for this response have not been examined yet. Thus, this study was designed to investigate the preventive effects of aerobic exercise training on the modulation of cellular mechanisms involved in the insulin-dependent glucose uptake pathway. The hypothesis of the present study was that aerobic exercise training attenuates the peripheral insulin resistance by preventing the decrease of protein level involved in glucose uptake pathway induced by Dexa.

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Table 1 Values of body, tibialis anterior weight, physical capacity, and blood glucose for all groups analyzed. SC

Weight (g)

a

Tibialis anterior (mg)/ tibia (cm) after Dexa treatment Physical capacity b (min) Blood glucose (mg/dl)

SD

TC

TD

Before

After

Before

After

Before

After

Before

After

treatment

treatment

treatment

treatment

treatment

treatment

treatment

treatment

472.0 ± 17.4 482.0 ± 18.9 (n = 10) (n = 10) 203.4 ± 7.1 (n = 10)

466.8 ± 25.3 330 ± 13.1 (n = 10) (n = 7) 147.8 ± 4.9* (n = 7)

443.6 ± 13.4 461.2 ± 12.8 (n = 10) (n = 10) 205.0 ± 7.1 (n = 10)

468.0 ± 19.9 331.0 ± 24.6 (n = 10) (n = 7) 119.3 ± 24.0* (n = 7)

9.0 ± 2.6 (n = 10) 85.9 ± 1.3 (n = 10)

8.6 ± 2.4 (n = 7) 80.5 ± 1.4 (n = 7)

8.5 ± 2.5 (n = 10) 87.4 ± 1.5 (n = 7)

9.4 ± 2.7 (n = 7) 84.0 ± 1.9 (n = 7)

6.9 ± 1.9 (n = 10) 87.5 ± 2.5 (n = 10)

8.0 ± 2.9 (n = 7) 206.4 ± 24.6* (n = 7)

14.7 ± 1.6 (n = 10) 84.9 ± 1.9 (n = 7)

14.2 ± 1.0 (n = 7) 168.8 ± 21.0*, + (n = 7)

a: Interaction between treatment and moment (all treated rats are different from control rats), p < 0.001 b: Interaction between training and moment (physical capacity from trained rats are different from sedentary rats), p < 0.001 *vs. respective control, p < 0.001;

+

vs. sedentary, p < 0.001

phospho IRS-1, 1:1,000 anti-total and phospho PKC-α or 1:1,000 anti-total and phospho-AKT. In a separate group of rats, 2 U · kg − 1 of insulin were administered 5 min prior to euthanasia to evaluate phosphorylated isoform level. Washed blots were then incubated with goat anti-rabbit secondary antibody at a dilution of 1:10,000 for 2 h at 22 °C and then subjected to the enhanced chemiluminescence substrate detection system (Super signal® West Pico, Pierce, Rockford, IL, USA). Immunoblotting and electrophoresis gels were performed as described previously [3]. Membranes were exposed to X-ray film (Kodak) for 2 min. More specifically, protein content was quantified by always exposing the film for a period of time that ensured that all signals were within the linear range of the detection of the film. Next, protein band intensity was quantified using Morphometry Imaging System (Scion Corporation, USA), and values were expressed according to the ratio between the phosphorylated and total protein level.

Statistical analysis All values are presented as mean ± S.E.M. Significant differences in the values measured among all groups were detected using a three-way ANOVA, with treatment and training as main independent factors and time (before and after) as repeated measurement (physical capacity, body weight, blood glucose, and ipGTT). Protein level among experimental groups was analyzed using two-way ANOVA. Significant differences were further investigated using a post-hoc test (Tukey) with statistical significance set at α < 0.05.

Results



Physical capacity of the trained animals (control + treated rats) increased approximately 50 % when compared with sedentary animals (p = 0.001), demonstrating that aerobic exercise training ▶ Table 1). Body weight was effective independent of treatment (● of animals at the beginning of the training protocol was similar. Additionally, weight gain during the training protocol showed similar trends among the groups. After 10 days of Dexa administration, sedentary and trained animals presented a significant ▶ Table 1. A reduction in body weight (p = 0.001) as shown in ● few rats died during Dexa treatment; therefore, the final number of rats in each group was different.

Fig. 1 Intraperitoneal glucose tolerance test (ipGTT; upper panel) in the 4 experimental groups after 10 days of treatment with Dexa: sedentary control group (SC, n = 8), sedentary Dexa-treated (SD, n = 6), trained control (TC, n = 8), and trained Dexa-treated (TD, n = 6). The area under the glucose curve (AUC; lower panel) was measured, and the results are expressed in arbitrary units. * vs. control and + vs. sedentary, p < 0.05. a Effects of treatment within sedentary group (p < 0.001). b Effects of treatment within trained group (p < 0.001). c Effects of training within treated group (p < 0.001).

The glucose levels prior to Dexa treatment were similar, how▶ Table 1). ever this treatment increased blood glucose levels (● An ipGTT at the end of the experimental period revealed that SD group presented higher level of blood glucose compared with SC group (p < 0.001). TD group showed higher levels of blood glu▶ Fig. 1, top panel, cose when compared with TC group (● p < 0.001). However, aerobic training attenuated the increase of

Dionísio TJ et al. Dexamethasone Side Effects and Exercise … Horm Metab Res 2014; 46: 484–489

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SC: Sedentary control; SD: Sedentary treated with Dexa; TC: Trained control; TD: Trained Dexa-treated

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▶ Fig. 2a shows that Dexa treatment caused a significant reduc●

Discussion



Fig. 2 a Upper panel: Western blot of total and phosphorylated insulin receptor substrate-1 (IRS-1) in the tibialis anterior (TA) muscle. Lower panel: Quantitative densitometry of the ratio between phosphorylated and total IRS-1 for all groups analyzed (n = 4): sedentary control group (SC), sedentary Dexa-treated (SD), trained control (TC) and trained Dexa-treated (TD). b Upper panel: Western blot of total and phosphorylated AKT in the tibialis anterior (TA) muscle. Lower panel: Quantitative densitometry of the ratio between phosphorylated and total AKT for all experimental groups. c Upper panel: Western blot of total and phosphorylated protein kinase C alpha (PKC-α) in the tibialis anterior (TA) muscle. Lower panel: Quantitative densitometry of the ratio between phosphorylated and total PKC-α for all experimental groups * vs. control and + vs. sedentary, p < 0.05.

blood glucose during ipGTT, since TD presented lower levels of blood glucose compared with SD (p = 0.001). In accordance, the AUC of Dexa-treated rats was 32.5 % higher than that of SC rats (p = 0.014). Aerobic exercise training attenuated the AUC values ▶ Fig. 1, lower panel, in treated animals ( − 37 % for TD vs. SD, ● p = 0.031).

In the present study, we have investigated the mechanisms responsible for the aerobic exercise-improvement of glucose uptake in Dexa treated rats. The main results showed, for the first time, that physical aerobic exercise completely prevented the decreases of AKT and IRS-1 protein level. These responses support the preventive role of aerobic exercise training on insulin resistance in skeletal muscle, which is the most important side effect of Dexa treatment. Dexa is widely used as an anti-inflammatory and anti-allergic drug. However, it causes negative side effects such as a dosedependent body weight reduction [3, 25], usually followed by muscle atrophy [3, 5, 25, 26]. In agreement, our results showed that Dexa treatment lead to a 30 % reduction from initial body weight of sedentary animals, and training did not avoid this reduction. Part of this response may be due to the reduction of food ingestion. Data from our laboratory have shown that food ingestion was 45 % lower in animals treated with Dexa compared with control animals (data not published). This reduction could be avoided if we had included a group of pair-feed control animals. We understand that this is a limitation of this study. The body weight was accompanied by TA muscle atrophy, as previously shown by Ahtikosky et al. [25] and confirmed by our group [3]. TA muscle atrophy may be explained because of the preferential effects of dexamethasone on MHC-2 isoform fibers [27]. One possible explanation for this higher responsiveness of dexamethasone on MHC2a/x and MHC-2b isoforms (predominant isoforms in TA muscle) is that these isoforms have lower succinate dehydrogenase activity under glucocorticoid treatment, which means less protective action against steroid induced atrophy [28]. It is documented that Dexa alters carbohydrate and lipid metabolism [3, 29, 30], and that most of these effects are dose-dependent. Although the dose used in this study may possibly be considered large, the amount of Dexa administered in this study (1 mg · kg –1 per day, i. p.) was previously validated by our collaborators [23, 29, 30] and by other independent authors [1, 5, 14, 25, 26]. This dose reliably triggers insulin resistance in animals. In this study, 10 days of Dexa administration caused hyperglycemia and higher area under the curve in ipGTT analyses suggesting a reduction in peripheral glucose uptake. This reduction may be caused by alterations in the insulin-signaling cascade. Some

Dionísio TJ et al. Dexamethasone Side Effects and Exercise … Horm Metab Res 2014; 46: 484–489

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tion in IRS-1 (p-IRS1/total IRS-1) protein level (–16 %) in sedentary animals compared with control (p = 0.015). Aerobic exercise training, performed before the treatment, prevented this reduction ( + 21 %, for TD vs. SD, p = 0.002). Ten days of Dexa treatment determined a significant reduction of p-AKT/total-AKT ratio (–43 %) in sedentary animals (p = 0.018). In fact, aerobic exercise promoted increases of 63 % for TC vs. SC ▶ Fig. 2b). (p = 0.0008) and 121 % for TD vs. SD (p = 0.022) (● ▶ Fig. 2c shows the protein level of PKC-α, represented by the ● ratio between p-PKC-α and total PKC-α. Dexa treatment did not cause a significant change in PKC-α protein level (p = 0.31). Similarly, PKC-α protein level was not altered by aerobic exercise training (p = 0.23).

of the works have shown significant increases in insulin levels and decreases in muscle glycogen content after Dexa treatment, suggesting peripheral insulin resistance [3, 23, 29]. Our data demonstrate that AUC (ipGTT) was decreased in trained animals treated with Dexa when compared with sedentary treated animals, which suggests that aerobic training significantly contributed to the improvement of peripheral glucose uptake by muscle tissue as shown previously [31, 32]. In this study we did not use the euglycemic, hyperinsulinemic clamp technique, which could better assess the insulin sensitivity. However, the results of the present study showed that Dexa treatment increased hyperglycemia in sedentary animals, and aerobic exercise prevented this deleterious effect in treated animals. It has been shown that both acute and chronic aerobic exercise training [33–35] may improve insulin-independent glucose signaling. However, so far little was known about the effects of aerobic exercise training on glucose uptake induced by insulin. Furthermore, to the best of our knowledge nothing is known about the preventive effects of aerobic exercise on alterations in insulin-stimulated glucose uptake in Dexa treated animals. Thus, our present study contributes to clarify the paucity of data regarding this subject by showing the level of 3 important proteins involved in glucose uptake. It has been reported that IRS-1 protein mediates insulin-stimulated glucose uptake. The results of the present study demonstrated that IRS-1 protein level was reduced by 16 % in the TA muscle after Dexa treatment in sedentary animals, which confirms the results previously demonstrated by others [1, 2, 8]. Also, it has been shown that Dexa treatment decreases IRS-1 level in other tissues such as adipocytes and myocytes [7, 36]. Furthermore, IRS-1 protein level appears to be sensitive to physical training, since swimming can increase IRS-1 protein level in rats [18]. However, some effects of aerobic exercise training are still controversial since a study found no increases in IRS-1 mRNA expression after aerobic exercise training [37]. In agreement with Wadley et al. [37] this present study failed to demonstrate a significant increase in IRS-1 induced by aerobic exercise training. It is important to note that IRS-1 protein level was completely preserved in TD group. Since IRS-1 is one of the first proteins produced in the insulin cascade that induces muscle glucose uptake, our hypothesis was that other proteins activated by IRS-1, such as AKT and PKC-α would be reduced after Dexa treatment. In accordance with our hypothesis, our results demonstrated that Dexa treatment decreased the ratio between p-AKT and total AKT by 43 % in the TA muscle of sedentary animals, which closely agrees with several studies in the literature [1, 6, 7, 9]. Many authors have shown that either acute aerobic exercise [20, 25, 38] or aerobic exercise training programs [17, 18, 38] increase both the level and the phosphorylation of AKT. In agreement with these studies, the present investigation found that the ratio between phosphorylated AKT and total AKT was 63 % higher in the TA muscle after aerobic exercise training when compared with sedentary control animals. Additionally, aerobic exercise training was effective in increasing AKT protein level in Dexa treated animals compared with sedentary animals. These results demonstrated the preventive role of aerobic exercise training on insulin signaling after Dexa treatment, which may be one of the mechanisms responsible for the improvement of insulin sensitivity in trained and Dexa treated animals.

Protein kinase C (PKC) seems to be an important protein involved in glucose uptake, mainly because it facilitates GLUT4 translocation to the membrane either activated by contraction stimulated pathways or insulin stimulated pathways [32]. On the other hand, some authors described that PKC is neither involved in insulin nor contraction-stimulated glucose uptake [34]. However, so far nothing is known about the Dexa effects on PKC-α protein level in skeletal muscle. Despite the fact that Dexa decreases GLUT-4 level, it has been suggested that PKC-α level may be directly related to GLUT-4 translocation to the membrane [11]. Therefore, one of the expected effects in this study was that PKC-α level would be reduced in skeletal muscle after Dexa treatment. However, the results of the present study did not confirm this hypothesis, since chronic treatment with Dexa did not cause changes in the PKC-α protein level in TA muscle. Some studies have documented increases in atypical PKC protein level induced by acute physical aerobic exercise. Perrini et al. [21] found increases in PKC-λ and -τ protein level in vastus lateralis muscle after acute physical aerobic exercise. Additionally, Rose et al. [22] found increases in atypical PKC activity in human vastus lateralis muscle after 40 min of aerobic exercise. However, this study showed that chronic aerobic exercise was not able to increase PKC-α protein level in TA muscle. Jensen et al. [34], in fact, demonstrated that PKC-α may not be important to the process of glucose uptake, since PKC-α knockout mice showed no harmful effects in glucose uptake after electrical stimulation in vitro on soleus muscle.

Conclusion



Taken together, the results of IRS-1 and AKT protein level suggest that Dexa reduces insulin-stimulated glucose uptake, at least in part, via reduction of AKT and IRS-1 protein level and that aerobic exercise training, conducted prior and concomitantly to drug treatment, prevented these side effects of Dexa. The results of this study reveal for the first time that aerobic exercise has a preventive role against the harmful side effects of Dexa treatment on the insulin-signaling pathway in skeletal muscle.

Acknowledgements



The authors thank Dr. Alex Rafacho for his contribution on the insulin experiments. We are grateful to Dr. Maria Oliveira de Souza for donating aliquots of the anti-phospho PKC-α primary antibody. The authors also thank FAPESP (São Paulo Research Foundation #2007/59770-9) and FUNDUNESP (Fundação para o Desenvolvimento da UNESP, #540/06), for the financial support. Matheus Barel (#2006/51936-2), Otavio A. B. Perez (#2006/519356), Juliana C. A. Louzada (#08/00821-6), and Daniel T. Brozoski (#2008/15372-5) were supported by a fellowship from FAPESP.

Conflict of Interest



The authors declare that they have no conflicts of interest in the authorship or publication of this contribution.

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Endocrine Research

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Aerobic training prevents dexamethasone-induced peripheral insulin resistance.

This study investigated how proteins of the insulin signaling cascade could modulate insulin resistance after dexamethasone (Dexa) treatment and aerob...
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