Remodeling of calcium handling in skeletal muscle through PGC-1α: impact on force, fatigability, and fiber type

Regular endurance exercise remodels skeletal muscle, largely through the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). PGC-1α promotes fiber type switching and resistance to fatigue. Intracellular calcium levels might play a role in both adaptive phenomena, yet a role for PGC-1α in the adaptation of calcium handling in skeletal muscle remains unknown. Using mice with transgenic overexpression of PGC-1α, we now investigated the effect of PGC-1α on calcium handling in skeletal muscle. We demonstrate that PGC-1α induces a quantitative reduction in calcium release from the sarcoplasmic reticulum by diminishing the expression of calcium-releasing molecules. Concomitantly, maximal muscle force is reduced in vivo and ex vivo. In addition, PGC-1α overexpression delays calcium clearance from the myoplasm by interfering with multiple mechanisms involved in calcium removal, leading to higher myoplasmic calcium levels following contraction. During prolonged muscle activity, the delayed calcium clearance might facilitate force production in mice overexpressing PGC-1α. Our results reveal a novel role of PGC-1α in altering the contractile properties of skeletal muscle by modulating calcium handling. Importantly, our findings indicate PGC-1α to be both down- as well as upstream of calcium signaling in this tissue. Overall, our findings suggest that in the adaptation to chronic exercise, PGC-1α reduces maximal force, increases resistance to fatigue, and drives fiber type switching partly through remodeling of calcium transients, in addition to promoting slow-type myofibrillar protein expression and adequate energy supply.     

Visualization of inflammation using (19) F-magnetic resonance imaging and perfluorocarbons

Inflammation plays a central pathophysiological role in a large number of diseases. While conventional magnetic resonance imaging (MRI) can depict gross tissue alterations due to proton changes, specific visualization of inflammation is an unmet task in clinical medicine. (19) F/(1) H MRI is a novel technology that allows tracking of stem and immune cells in experimental disease models after labelling with perfluorocarbon (PFC) emulsions. (19) F markers such as PFC compounds provide a unique signal in vivo due to the negligible (19) F background signal of the body. Concomitant acquisition of (1) H images places the labelled cells into their anatomical context. This novel imaging technique has been applied to monitor immune cell responses in myocardial infarction, pneumonia, bacterial abscess formation, peripheral nerve injury, and rejection of donor organs after transplantation. Upon systemic application PFC nanoparticles are preferentially phagozytosed by circulating monocytes/macrophages and, thus, the fluorine signal in inflamed organs mainly reflects macrophage infiltration. Moreover, attenuation of the inflammatory response after immunosuppressive or antibiotic treatments could be depicted based on (19) F/(1) H-MRI. Compared to other organ systems (19) F-MRI of neuroinflammation is still challenging, mainly because of lack in sensitivity. In focal cerebral ischemia early application of PFCs revealed ongoing thrombotic vessel occlusion rather than cell migration indicating that timing of contrast agent application is critical. Current restrictions of (19) F/(1) H-MRI in sensitivity may be overcome by improved imaging hardware, imaging sequences and reconstruction techniques, as well as improved label development and cell labelling procedures in the future.     

Oxidative stress‐induced structural changes in the microtubule‐associated flavoenzyme Irc15p from Saccharomyces cerevisiae

The genome of the yeast Saccharomyces cerevisiae encodes a canonical lipoamide dehydrogenase (Lpd1p) as part of the pyruvate dehydrogenase complex and a highly similar protein termed Irc15p (increased recombination centers 15). In contrast to Lpd1p, Irc15p lacks a pair of redox active cysteine residues required for the reduction of lipoamide and thus it is very unlikely that Irc15p performs a similar dithiol‐disulfide exchange reaction as reported for lipoamide dehydrogenases. We expressed IRC15 in Escherichia coli and purified the produced protein to conduct a detailed biochemical characterization. Here, we show that Irc15p is a dimeric protein with one FAD per protomer. Photoreduction of the protein generates the fully reduced hydroquinone without the occurrence of a flavin semiquinone radical. Similarly, reduction with NADH or NADPH yields the flavin hydroquinone without the occurrence of intermediates as observed for lipoamide dehydrogenase. The redox potential of Irc15p was ?313 ± 1 mV and is thus similar to lipoamide dehydrogenase. Reduced Irc15p is oxidized by several artificial electron acceptors such as potassium ferricyanide, 2,6‐dichlorophenol‐indophenol, 3‐(4,5‐dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide, and menadione. However, disulfides such as cystine, glutathione, and lipoamide were unable to react with reduced Irc15p. Limited proteolysis and SAXS‐measurements revealed that the NADH‐dependent formation of hydrogen peroxide caused a substantial structural change in the dimeric protein. Therefore, we hypothesize that Irc15p undergoes a conformational change in the presence of elevated levels of hydrogen peroxide, which is a putative biomarker of oxidative stress. This conformational change may in turn modulate the interaction of Irc15p with other key players involved in regulating microtubule dynamics.     

Peroxisome proliferator‐activated receptor γ coactivator 1α regulates mitochondrial calcium homeostasis,sarcoplasmic reticulum stress,and cell death to mitigate skeletal muscle aging

Age‐related impairment of muscle function severely affects the health of an increasing elderly population. While causality and the underlying mechanisms remain poorly understood, exercise is an efficient intervention to blunt these aging effects. We thus investigated the role of the peroxisome proliferator‐activated receptor γ coactivator 1α (PGC‐1α), a potent regulator of mitochondrial function and exercise adaptation, in skeletal muscle during aging. We demonstrate that PGC‐1α overexpression improves mitochondrial dynamics and calcium buffering in an estrogen‐related receptor α‐dependent manner. Moreover, we show that sarcoplasmic reticulum stress is attenuated by PGC‐1α. As a result, PGC‐1α prevents tubular aggregate formation and cell death pathway activation in old muscle. Similarly, the pro‐apoptotic effects of ceramide and thapsigargin were blunted by PGC‐1α in muscle cells. Accordingly, mice with muscle‐specific gain‐of‐function and loss‐of‐function of PGC‐1α exhibit a delayed and premature aging phenotype, respectively. Together, our data reveal a key protective effect of PGC‐1α on muscle function and overall health span in aging.     

Fasergliastruktur der dorsalen Wand des Aquaeductus cerebri bei einigen Primaten

Zusammenfassung Bei Ateles, Cebus, Macaca und Pan wird die Architektonik der subependymalen Astroglia im ersten dorsalen Drittel des Aquaeductus cerebri und der marginalen Glia in der Commissura posterior und im Tectum beschrieben. Am Dach des Aquaeductus cerebri sind regionale Unterschiede in der subependymalen Fasertextur zu erkennen; den einzelnen Regionen entsprechen bestimmte Gliazelltypen. Verschiedenheiten zeigt auch die Anordnung der marginalen Glia der Commissura posterior und des Tectum. Zwischen der subependymalen Gliafaserdeckschicht des Subcommissuralorgans bzw. des Recessus mesocoelicus und der marginalen Glia der Commissura posterior besteht ein direkter Strukturzusammenhang. Diesen vermitteln kräftige perivasculäre Radiärfaserbündel, an die sich z.T. auch noch bipolare Tanycytenformen (Recessus mesocoelicus) anschließen. Zwischen der subependymalen Gliafaserdeckschicht des Aquaeductus cerebri und der marginalen Glia des Tectum läßt sich dagegen keine direkte Verbindung nachweisen. Eine mechanische (statische) Funktion der in der vorliegenden und in einer früheren Studie (Merker, 1968) beobachteten Gliatexturen wird diskutiert.

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The structure of fibrous astroglia in the dorsal wall of the cerebral aqueduct in some primates

Summary The structure and architecture of the subependymal astrocytes of the first third of the roof of the cerebral aqueduct and the marginal glia of the posterior commissure and of the tectum were studied in Ateles, Cebus, Macaca, and Pan. Regional differences in the types of subependymal astrocytes were observed in the roof of the cerebral aqueduct. The marginal glia of the posterior commissure and of the tectum also had special structural patterns. A direct structural connexion was found to exist between the subependymal glial layer of the subcommissural complex, or the recessus mesocoelicus, and the marginal glia of the posterior commissure. The connexion was characterized by coarse radial perivascular fiber bundles, supported to some extent by bipolar gliocytes. No junctional arrangement, however, was seen between the subependymal fiber layer of the cerebral aqueduct and the marginal fibrous glia of the tectum. The observations suggested that the astroglial formations may have a mechanical function.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Trisomy of human chromosome 18: Molecular studies on parental origin and cell stage of nondisjunction

We investigated the parent and cell division of origin of the extra chromosome 18 in 62 aneuploids with a free trisomy 18 by using chromosome-18-specific pericentromeric short-sequence repeats. In 46 cases, DNA of patients was recovered from archival specimens, such as paraffin-embedded tissues and fixed chromosomal spreads. In 56 families, the supernumerary chromosome was maternal in origin; in six families, it was paternal. Among the 56 maternally derived aneuploids, we could exclude a postzygotic mitotic error in 52 cases. Among those in which the nondisjunction was attributable to an error at meiosis, 11 were the result of a meiosis I nondisjunction and 17 were caused by a meiosis II error. This result differs markedly from findings in acrocentric chromosomes where nondisjunction at maternal meiosis I predominates. Among the six paternally derived cases, two originated from a meiotic error, indicating that a nondisjunction in paternal meiosis is not as rare as previously suggested.Dedicated to Professor Dr. W. Gottschalk on the occasion of his 75th birthday     

High resolution measurements of sediment resuspension above an accumulation bottom in a stratified lake

A detailed record of suspended particulate matter (SPM) concentrations in the benthic boundary layer (BBL) 1.5 m above an accumulation bottom and 13.5 m below the surface was obtained from frequent (30 min interval) beam attenuation measurements made with a Sea Tech transmissometer in the main basin of Lake Erken, a moderately deep (mean depth 9 m, maximum depth 21 m) dimictic lake in central Sweden. Concentrations of SPM (g m^–3) were not as strongly correlated to the beam attenuation coefficient (c, [m^–1]), as were concentrations of the inorganic SPM fraction. Apparently, this was caused by large optically inactive organic particles which significantly affected the measurements of SPM, but had little effect on the attenuation of light.When the water column was thermally stratified, SPM concentrations in the BBL showed a seasonal increase which was related to an increase in the thermocline depth. As the epilimnion deepened, there was also a marked increase in the occurrence of rapid and large changes in SPM concentration. After the loss of stratification, the amount of SPM and the temporal variability in its concentration was reduced. Since surface waves could not influence sediment resuspension at the depth of measurement, these data show the importance of internal waves in promoting sediment resuspension in areas of sediment accumulation. The relatively short period in each summer, when the thermocline reaches a sufficient depth to allow for resuspension over accumulation bottoms, can have important consequences for both the redistribution of lake sediments and the internal loading of phosphorus.     

Early remodelling of the extracellular matrix proteins tenascin‐C and phosphacan in retina and optic nerve of an experimental autoimmune glaucoma model

Glaucoma is characterized by the loss of retinal ganglion cells (RGCs) and optic nerve fibres. Previous studies noted fewer RGCs after immunization with ocular antigens at 28 days. It is known that changes in extracellular matrix (ECM) components conduct retina and optic nerve degeneration. Here, we focused on the remodelling of tenascin‐C and phosphacan/receptor protein tyrosine phosphatase β/ζ in an autoimmune glaucoma model. Rats were immunized with optic nerve homogenate (ONA) or S100B protein (S100). Controls received sodium chloride (Co). After 14 days, no changes in RGC number were noted in all groups. An increase in GFAP mRNA expression was observed in the S100 group, whereas no alterations were noted via immunohistochemistry in both groups. Extracellular matrix remodelling was analyzed after 3, 7, 14 and 28 days. Tenascin‐C and 473HD immunoreactivity in retinae and optic nerves was unaltered in both immunized groups at 3 days. At 7 days, tenascin‐C staining increased in both tissues in the ONA group. Also, in the optic nerves of the S100 group, an intense tenascin‐C staining could be shown. In the retina, an increased tenascin‐C expression was also observed in ONA animals via Western blot. 473HD immunoreactivity was elevated in the ONA group in both tissues and in the S100 optic nerves at 7 days. At 14 days, tenascin‐C and 473HD immunoreactivity was up‐regulated in the ONA retinae, whereas phosphacan expression was up‐regulated in both groups. We conclude that remodelling of tenascin‐C and phosphacan occurred shortly after immunization, already before RGC loss. We assume that both ECM molecules represent early indicators of neurodegeneration.     

Histochemical localization of Mg2+-activated ATPases on microtubule bundles in epidermal cells of Carausius morosus: Possible significance to pigment migration

We have demonstrated the presence of Mg²⁺-stimulated ATPases on microtubule bundles in the epidermal cells at the light microscope level, using specific histochemical techniques. This method provides an alternative method to immunohistochemistry for identifying microtubule bundles in the epidermal cells of Carausius morosus using the light microscope. The close association between ommochrome granules and the microtubule bundles support the hypothesis, that these ATPases play an important role in force generation, required to move ommochrome granules during physiological colour change.