Increased glucocorticoid/androgen receptor ratios in denervated striated muscle

A neural mechanism of nuclear receptor expression and regionalization

Spatially restricted expression of genes by global circulating inducers (hormones, secreted proteins, growth factors, neuromodulators, etc.) was a prerequisite for the evolution of animals. Far from a random occurrence, it is a systematically occurring, certain event, implying that specific information is invested for it to happen. In this minireview, we show for the first time that the expression and regionalization takes place at the level of receptors via a neural mechanism and make an attempt to reconstruct the causal chain from neural signaling to expression of nuclear receptors.

Hormonal Treatment Effects on the Cross-sectional Area of Pubococcygeus Muscle Fibers After Denervation and Castration in Male Rats

We explore the interaction of muscle innervation and gonadal hormone action in the pubococcygeus muscle (Pcm) after castration and hormone replacement. Male Wistar rats were castrated and the Pcm was unilaterally denervated; after 2 or 6 weeks, the cross-sectional area (CSA) of Pcm fibers was assessed. Additional groups of castrated rats were used to examine the effects of hormone replacement. At 2 weeks post surgeries, rats were implanted with Silastic capsules containing either dihydrotestosterone (DHT), estradiol benzoate (EB) or both hormones, and the CSA of Pcm fibers was assessed after 4 weeks of hormone treatment. At 2 weeks post surgeries, gonadectomy without hormone replacement resulted in reductions in the CSA of Pcm fibers, and denervation combined with castration increased the magnitude of this effect; further reductions in CSA were present at 6 weeks post surgeries, but again denervation combined with castration increased the magnitude of this effect. Hormone replacement with DHT resulted in hypertrophy in the CSA of nondenervated muscles compared to those of intact normal males, but this effect was attenuated in denervated muscles. Hormone replacement with EB treatment prevented further castration-induced reductions in CSA of nondenervated muscles, but denervation prevented this effect. Similar to that seen with treatment with EB alone, combined treatment with both DHT and EB prevented further reductions in CSA of Pcm fibers in nondenervated muscles, but again denervation attenuated this effect. Thus, while hormone replacement can reverse or prevent further castration-induced atrophy of Pcm fibers, these effects are dependent on muscle innervation. Anat Rec, 300:1327-1335, 2017. © 2017 Wiley Periodicals, Inc.

Critical illness myopathy: sepsis-mediated failure of the peripheral nervous system

With better survival of critically ill patients, 'de novo' arising neuromuscular complications like critical illness myopathy or polyneuropathy have been increasingly observed. Prolonged hospitalization not only imposes risks like pneumonia or thrombosis on patients but also represents a real budget threat to modern intensive-care medicine. Clinical symptoms like muscle weakness and weaning failure are common to critical illness myopathy and critical illness polyneuropathy and do not allow for distinction. Specific therapies are not yet available, and the quest for the pathomechanisms has proved more complicated than anticipated. Especially for critical illness myopathy, multiple sites of disturbances to the excitation-contraction coupling cascade are possible causes of muscle weakness. The present review summarizes the epidemiological, clinical and diagnostic features of critical illness myopathy and then focuses on current concepts of the presumed pathomechanisms of critical illness myopathy. Sepsis was shown to be a major cause of critical illness myopathy and special emphasis will be placed on how sepsis and inflammatory mediators influence (i) the membrane excitability at the level of voltage-gated ion channels and (ii) the intracellular protein signalling that results in selective loss of myosin protein content and muscle wasting. For (i), critical illness myopathy represents a new type of acquired channelopathy affecting the inactivation properties of Na+ channels. For (ii), both protein proteolysis and protein build up at the transcriptional level seem to be involved. Findings from different studies are put into a common context to propose a model for cytokine-mediated failure of muscle in severe sepsis. This can open a series of new possible trials to test specific therapeutic strategies in the future.

Glucocorticoid receptor concentrations in muscle biopsies from patients with neuromuscular diseases

Increases in circulating glucocorticoids promote catabolism, particularly in skeletal muscle. The sensitivity of the muscle to glucocorticoids can be altered by a change in the number of glucocorticoid receptors in the muscle, or by a change in the proportions of activated receptors (between binders IB and II). We have investigated the concentration of glucocorticoid receptors, and the proportions of types IB and II, in healthy and diseased muscle. We found significantly reduced concentrations of glucocorticoid receptors in the group of inflammatory myopathies (51% reduction; P < 0.05, Wilcoxon signed rank test). No significant changes in the relative proportions of binders IB and II were found in pathological muscle, although the proportion of binder IB tended towards elevated values (especially in the diabetic neuropathies, with a 17% increase). We conclude that the sensitivity of muscle to glucocorticoids can be reduced in neuromuscular diseases, especially in myositis, by a reduction in the number of glucocorticoid receptors in the tissue, but that no relevant shift in the relation between activated receptor types is present. This could be important in relation to the risk of a secondary steroid myopathy and catabolism of skeletal muscle in the treatment of inflammatory myopathies with glucocorticoids.

Steroid and neuronal regulation of ecdysone receptor expression during metamorphosis of muscle in the moth, Manduca sexta

Ecdysteroids regulate the remodeling of the dorsal external oblique 1 (DEO1) muscle during metamorphosis in Manduca sexta (). We show that the temporal and spatial patterning of the A and B1 isoforms of the ecdysone receptor (EcR) within muscle DEO1 corresponds with the developmental fates of the fibers. Using antibodies directed to specific isoforms of EcR, we show that the expression of various EcR isoforms in myonuclei differ among the five fibers of DEO1 and correspond with the developmental response of the muscle to the changing steroid titers and to the pattern of innervation. Muscle degeneration and apoptosis of myonuclei in all fibers are correlated with the expression of only EcR-A just before pupal ecdysis and then with the expression of low levels of both EcR-A and EcR-B1 shortly after pupation. Only the first fiber of muscle DEO1 participates in the regrowth of the adult muscle, and only this fiber shows an upregulation of EcR-B1 that is evident at 3 d after pupal ecdysis. Denervation of the muscle prevents both the upregulation of EcR-B1 and myoblast proliferation. We conclude that the developmental fate of muscle DEO1 during metamorphosis is orchestrated by interactions between rising and falling ecdysteroid titers, the pattern of expression of EcR isoforms by the muscle, and interactions with other cells in the local environment.

Androgen locally regulates rat bulbocavernosus and levator ani size

Adult male rats were gonadectomized, and small Silastic capsules filled with hormone were sutured to each bulbocavernosus and levator ani muscle complex (BC/LA). In the first experiment, one capsule contained testosterone (T), while the capsule on the contralateral muscles contained the antiandrogen hydroxyflutamide (hFl). The intent of this treatment was to provide a focus of androgenic stimulation to the muscles on one side. After 30 days, animals were sacrificed, and the BC/LA muscle pairs were removed, weighed, and compared. BC/LAs receiving T treatment were heavier than those receiving hFl treatment (p less than 0.0001), with an average weight difference of 12%. Muscle fibers from T-treated BCs were significantly larger in diameter than those from contralateral, hFl-treated BCs. These results indicate that androgen exerts its anabolic effect by acting locally upon a cell population within or near the BC/LA. When hFl and blank capsules were implanted in castrated males, the hFl-treated muscles were significantly heavier (by 9%), demonstrating an anabolic effect of hFl in the absence of androgen, and refuting the idea that hFl may have caused local toxic effects in the first experiment. Gonadectomized animals given T versus blank capsules had T-treated muscles that were 8% heavier than the blank-treated side. Muscle weights were also compared in animals receiving bilateral denervation of the BC/LA at the time of T and hFl capsule implantation and gonadectomy; local testosterone treatment failed to affect BC/LA weights in these denervated muscles.

Evidence for androgen receptors in sexually dimorphic perineal muscles of neonatal male rats. Absence of androgen accumulation by the perineal motoneurons

During development, survival of the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) and its target perineal muscles, the bulbocavernosus (BC) and the levator ani (LA) is androgen-dependent. To define androgen's site of action in masculinizing SNB system structures, we examined whether or not androgen receptors are present in SNB motoneurons and/or BC/LA muscles of neonatal male rats. Using a receptor binding assay, we have identified androgen-binding factors in the neonatal BC/LA (Bmax = 13.5 fmol/mg protein; Kd = 4.69 nM) for the first time. In contrast, androgen autoradiography provided no evidence that neonatal spinal motoneurons accumulate androgens. These results support the hypothesis that BC/LA muscles are a primary site of androgen action for masculinizing SNB system structures, and that androgen need not interact with SNB motoneurons directly to sexually differentiate them.