Transcriptional and posttranscriptional mechanisms modulate creatine kinase expression during differentiation of osteoblastic cells

Creatine supplementation for older adults: Focus on sarcopenia, osteoporosis, frailty and Cachexia

Sarcopenia refers to the age-related reduction in strength, muscle mass and functionality which increases the risk for falls, injuries and fractures. Sarcopenia is associated with other age-related conditions such as osteoporosis, frailty and cachexia. Identifying treatments to overcome sarcopenia and associated conditions is important from a global health perspective. There is evidence that creatine monohydrate supplementation, primarily when combined with resistance training, has favorable effects on indices of aging muscle and bone. These musculoskeletal benefits provide some rationale for creatine being a potential intervention for treating frailty and cachexia. The purposes of this narrative review are to update the collective body of research pertaining to the effects of creatine supplementation on indices of aging muscle and bone (including bone turnover markers) and present possible justification and rationale for its utilization in the treatment of frailty and cachexia in older adults.

Effectiveness of Creatine Supplementation on Aging Muscle and Bone: Focus on Falls Prevention and Inflammation

Sarcopenia, defined as the age-related decrease in muscle mass, strength and physical performance, is associated with reduced bone mass and elevated low-grade inflammation. From a healthy aging perspective, interventions which overcome sarcopenia are clinically relevant. Accumulating evidence suggests that exogenous creatine supplementation has the potential to increase aging muscle mass, muscle performance, and decrease the risk of falls and possibly attenuate inflammation and loss of bone mineral. Therefore, the purpose of this review is to: (1) summarize the effects of creatine supplementation, with and without resistance training, in aging adults and discuss possible mechanisms of action, (2) examine the effects of creatine on bone biology and risk of falls, (3) evaluate the potential anti-inflammatory effects of creatine and (4) determine the safety of creatine supplementation in aging adults.

Creatine Monohydrate Increases Bone Mineral Density in Young Sprague-Dawley Rats

INTRODUCTION

Creatine kinase, found in osteoblasts, is an enzyme that is upregulated in response to interventions that enhance bone mass accretion. Creatine monohydrate supplementation can increase fat-free mass in young healthy men and women and can reduce markers of bone breakdown in boys with Duchenne muscular dystrophy.

PURPOSE

The objective of this study was to determine the influence of supplementation with creatine monohydrate on bone structure and function in growing rats, to establish a therapeutic model.

MATERIALS AND METHODS

Creatine monohydrate (2% w.w.) (CR; N = 16) or standard rat chow (CON; N = 16) was fed to Sprague-Dawley rats beginning at 5 wk of age, for 8 wk. Bone mineral density (BMD) and content (BMC) were assessed using dual-energy x-ray absorptiometry at the beginning and end of the protocol. The rats were sacrificed, and one femur was removed for the determination of mechanical properties.

RESULTS

The CR-treated rats showed greater lumbar BMD and femoral bending load at failure compared with the CON rats (P < 0.05).

CONCLUSIONS

Together, these data suggest that creatine monohydrate potentially has a beneficial influence on bone function and structure; further investigation is warranted into its effect on bone functional properties and its effects in disorders associated with bone loss.

Ankyrin repeat and suppressors of cytokine signaling box protein asb-9 targets creatine kinase B for degradation

The suppressors of cytokine signaling (SOCS) proteins inhibit cytokine action by direct interaction with Janus kinases or activated cytokine receptors. In addition to the N-terminal and Src homology 2 domains that mediate these interactions, SOCS proteins contain a C-terminal SOCS box. DNA data base searches have identified a number of other protein families that possess a SOCS box, of which the ankyrin repeat and SOCS box-containing (Asb) proteins constitute the largest. Although it is known that the SOCS proteins are involved in the negative regulation of cytokine signaling, the biological and biochemical functions of the Asbs are largely undefined. Using a proteomics approach, we demonstrate that creatine kinase B (CKB) interacts with Asb-9 in a specific, SOCS box-independent manner. This interaction increases the polyubiquitylation of CKB and decreases total CKB levels within the cell. The targeting of CKB for degradation by Asb-9 was primarily SOCS box-dependent and suggests that Asb-9 acts as a specific ubiquitin ligase regulating levels of this evolutionarily conserved enzyme.

Creatine kinase is an alpha myosin heavy chain 3'UTR mRNA binding protein

Altered cardiac workload regulates the translation and localization of the alpha myosin heavy chain (alphaMyHC) messenger RNA through the 3' untranslated region (UTR) by protein-RNA interactions. We used the alphaMyHC 3'UTR from neonatal rat heart tissue in a gel shift analysis to find RNA binding proteins. One was identified by microsequencing as creatine kinase, brain form B (CKBB). The affinity of its binding interaction was evaluated using sense and antisense alphaMyHC 3'UTR and 3'UTR probes from myosin isoforms of 2B and 2X skeletal muscle. Removal of calcium by the chelating agent EGTA had a potentiating effect on the formation of the CKBB/alphaMyHC 3'UTR complex in vitro . Varying the concentration of ATP (0.1-1 mM) also enhanced this interaction, suggesting that autophosphorylation of CKBB is taking place. Our novel finding that CKBB, an energy transduction enzyme, binds to the RNA of the 3'UTR of the faster ATP consuming alphaMyHC suggests a possible regulatory linkage between the metabolic state of the cell and myosin isoform expression.

Differential expression of duplicated opsin genes in two eyetypes of ostracod crustaceans

In the first molecular study of ostracod (Crustacea) vision, we present partial cDNA sequences of ostracod visual pigment genes (opsins). We found strong support for differential expression of opsins in ostracod median and compound eyes and suggest that photoreceptor specific expression may be a general phenomenon in organisms with multiple receptors. We infer that eye-specific expression predates the divergence of the two species examined, Skogsbergia lerneri and Vargula hilgendorfii, because eye-specific opsin orthologs are present in both species. We found multiple opsin loci in ostracods, estimating that at least eight are present in Skogsbergia lerneri. All opsins from both ostracod species examined are more closely related to each other than to any other known opsin sequences. Because we find no evidence for gene conversion or alternative splicing, we suggest the occurrence of many recent gene duplications. Why ostracods may have retained multiple recent opsin gene duplicates is unknown, but we discuss several possible hypotheses.

Identification of putative downstream genes of Oct-4 by suppression-subtractive hybridization

As a step toward understanding how toti/pluripotence is maintained by Oct-4, we have first constructed a cell model with differentially expressed Oct-4 in embryonic stem cells, and then used suppression-subtractive hybridization (SSH) method to identify the downstream genes of Oct-4. Among the 384 clones we screened, 40 clones were detected as differentially expressed genes with colony hybridization, and 13 clones were confirmed as the putative downstream genes of Oct-4 by Northern blot analysis. Sequencing showed 12 different genes, 8 known genes (Oct-4, Rex-1, Sox-2, Creatine kinase B, Makorin 1, Importin beta, Histone H2A.Z, Ribosomal protein S7) and 4 new genes. Except Oct-4 and Rex-1, the other genes have not been reported to be regulated by Oct-4. These results showed that SSH provides a very efficient means to identify the downstream genes of transcription factor. Some known genes identified may provide new insight of the function of Oct-4 in stem cells.

Acute changes of myocardial creatine kinase gene expression under beta-adrenergic stimulation

Creatine kinase (CK) plays a crucial role in myocardial energy metabolism. Alterations in CK gene expression are found in hypertrophied and failing heart, but the mechanisms behind these changes are unclear. This study tests the hypothesis that increased adrenergic stimulation, which is observed in heart failure, induces changes of myocardial CK-activity, -isoenzyme distribution and -gene expression that are characteristic of the failing and hypertrophied heart. Isolated rat hearts were perfused (constant pressure of 80 mmHg) with red cell suspensions. Following a 20-min warm-up period, perfusion for 3 h with 10(-8) M (iso 3 h) or without (control 3 h) isoproterenol was started or experiments were immediately terminated (control 0 h). Left ventricular tissue was analyzed for total CK-activity, CK-isoenzyme distribution and, by use of quantitative RT-PCR, for B-CK, M-CK, mito-CK and GAPDH- (as internal standard) mRNA. After beta-adrenergic stimulation (iso 3 h) but not after control perfusion (control 3 h) a roughly threefold increase in B-CK mRNA levels and a decrease in M-CK mRNA levels by 18% was found. There were no significant differences among the three groups in total CK-activity and in distribution of CK-MM, CK-BB, CK-MB and mito-CK. Thus, beta-adrenergic stimulation induces a switch in CK gene expression from M-CK to B-CK, which is characteristic for the hypertrophied and failing heart. This may be interpreted as an adaptive mechanism making energy transduction via CK more efficient at times of increased metabolic demand.

Crystal structure of brain-type creatine kinase at 1.41 A resolution

Excitable cells and tissues like muscle or brain show a highly fluctuating consumption of ATP, which is efficiently regenerated from a large pool of phosphocreatine by the enzyme creatine kinase (CK). The enzyme exists in tissue--as well as compartment-specific isoforms. Numerous pathologies are related to the CK system: CK is found to be overexpressed in a wide range of solid tumors, whereas functional impairment of CK leads to a deterioration in energy metabolism, which is phenotypic for many neurodegenerative and age-related diseases. The crystal structure of chicken cytosolic brain-type creatine kinase (BB-CK) has been solved to 1.41 A resolution by molecular replacement. It represents the most accurately determined structure in the family of guanidino kinases. Except for the N-terminal region (2-12), the structures of both monomers in the biological dimer are very similar and closely resemble those of the other known structures in the family. Specific Ca2+-mediated interactions, found between two dimers in the asymmetric unit, result in structurally independent heterodimers differing in their N-terminal conformation and secondary structure. The high-resolution structure of BB-CK presented in this work will assist in designing new experiments to reveal the molecular basis of the multiple isoform-specific properties of CK, especially regarding different subcellular locations and functional interactions with other proteins. The rather similar fold shared by all known guanidino kinase structures suggests a model for the transition state complex of BB-CK analogous to the one of arginine kinase (AK). Accordingly, we have modeled a putative conformation of CK in the transition state that requires a rigid body movement of the entire N-terminal domain by rms 4 A from the structure without substrates.

Muscle-specific transcription factors in fibroblasts expressing the alpha-striated tropomyosin 3' untranslated region

The alpha-striated tropomyosin 3' untranslated region (TM UTR) promotes differentiation of fibroblasts into cells resembling skeletal muscle. To investigate the mechanism of this observation, RNA harvested from transfected primary fibroblasts was used for semiquantitative RT-PCR with primers specific for muscle transcription factors, showing that myoD and myogenin transcripts are detected in these cells, but that differentiation after TM UTR expression is independent of a detectable increase in these transcripts. Double immunofluorescent staining with antibodies to myoD family members and to titin confirms that muscle differentiation in TM UTR-transfected fibroblasts is independent of production of any transcription factor in this family. In contrast, the muscle transcription factor myocyte enhancer factor 2 (mef-2) is strongly expressed after transfection of fibroblasts with the TM UTR. The increase in mef-2 protein is due to an increase in the steady-state level of its mRNA, as shown by Northern analysis. The expression of p21 ordinarily observed in skeletal myogenesis before the expression of muscle-specific proteins is not seen in fibroblasts induced to differentiate by the TM UTR. These results demonstrate that post-transcriptional regulation of myoD family members is seen in fibroblasts, and that the TM UTR induces muscle differentiation independent of the myoD transcription factors and without expressing proteins characteristic of terminal withdrawal from the cell cycle. Finally, an increase in the steady-state level of mef-2 transcripts appears in the proximal pathway of myogenic activation in response to expression of the TM UTR. These results imply that fibroblasts can utilize an additional differentiation route upon TM UTR expression resulting in mature muscle other than that requiring myoD family members.

Glucocorticoids decrease interleukin-6 levels and induce mineralization of cultured osteogenic cells from children with fibrous dysplasia

Fibrous dysplasia (FD) is a progressive bone disease in which abnormal fibroblast proliferation results in the replacement of normal cancellous bone with an immature fibrous tissue that is poorly mineralized. The disease manifests itself in the monostotic form in which only one bone is involved and the polyostotic form in which multiple bones at different sites are affected. The McCune-Albright syndrome is a variation of the polyostotic form in which patients demonstrate a greater extent of bone involvement and a variety of endocrinopathies. Somatic activating mutations in the GNAS gene have been demonstrated in the fibrotic lesions of patients affected with either monostotic or polyostotic FD. The increased cAMP levels caused by the G-protein mutations lead to increased interleukin-6 (IL-6) levels in the affected tissues, resulting in abnormal osteoblast differentiation and increased osteoclastic activity. Utilizing cell culture techniques that have been developed for mammalian bone marrow stromal cells, we have successfully cultured osteogenic stem cells from the affected stroma of 11 FD patients. Cells cultured from patients with polyostotic FD showed a high frequency of the Gsalpha mutation, whereas cells from monostotic FD patients showed a low frequency of the mutation. Both the normal and FD cells displayed the osteogenic phenotype when exposed to medium containing glucocorticoids. Glucocorticoids also caused a dramatic inhibition of IL-6 mRNA and protein levels in osteogenic cells cultured from the FD patients. These findings suggest that chemical alteration of cellular function may lead to new treatment options for patients with FD.

Characterization of a nuclear protein that interacts with regulatory elements in the human B creatine kinase gene

The B creatine kinase gene is regulated by an array of positive and negative cis-elements in the 5'-flanking DNA that function in both muscle and nonmuscle cells. In C2C12 myogenic cells M and B creatine kinase mRNAs are coordinately up-regulated in the early stages of myogenesis and then undergo distinct regulatory programs. The B creatine kinase gene is down-regulated in the late stages of myogenesis as M creatine kinase becomes the predominant species in mature myotubes. Sequences between -92 and +80 of the B creatine kinase gene confer a regulated pattern of expression to chimeric plasmids that closely resembles the time-course of expression of the endogenous B creatine kinase gene in C2C12 cells undergoing differentiation. We show that sequences within the first exon of the B creatine kinase gene are important for the development regulation of the gene in C2C12 cells and that these sequences bind a nuclear protein that shows a similar tissue-specific distribution and developmentally regulated expression to that of the endogenous B creatine kinase gene.

Mouse ubiquitous mitochondrial creatine kinase: gene organization and consequences from inactivation in mouse embryonic stem cells

Individual members of the creatine kinase isoenzyme family (CK; EC 2.7.3.2), which play a prominent role in energy homeostasis, are encoded by four separate nuclear genes. We have isolated and characterized the complete mouse UbCKmit gene, the product of which is ubiquitously expressed and is located in the intermembrane space of mitochondria. Transcription of this gene is initiated at multiple adjacent positions and the region immediately upstream of these sites shares many features with genes encoding housekeeping proteins. These include a high G/C content, absence of TATA and CCAAT motifs, and presence of SP1 and AP2 recognition sequences. In addition, a binding site for HIP1, hormone-responsive elements, and three Mt-motifs, known as boxes shared between nuclear genes encoding mitochondrial proteins, were identified. To study the functional role of the UbCKmit protein, we have inactivated both UbCKmit alleles in mouse embryonic stem (ES) cells. UbCKmit-deficient cells, obtained by consecutive rounds of gene targeting using homologous recombination and drug selection-driven gene conversion events, show no obvious growth disadvantage or abnormal differentiation potential. Activities of mitochondrial cytochrome c oxidase and citrate synthase, as well as the rate of pyruvate oxidation, showed values equal to wild-type cells, indicating a normal aerobic metabolism. Mitochondria of in vivo differentiated knock-out cells were structurally intact, as demonstrated by electron microscopy. Approaches to study the role of the UbCKmit gene further are discussed.

Creatine kinase in non-muscle tissues and cells

Over the past years, a concept for creatine kinase function, the 'PCr-circuit' model, has evolved. Based on this concept, multiple functions for the CK/PCr-system have been proposed, such as an energy buffering function, regulatory functions, as well as an energy transport function, mostly based on studies with muscle. While the temporal energy buffering and metabolic regulatory roles of CK are widely accepted, the spatial buffering or energy transport function, that is, the shuttling of PCr and Cr between sites of energy utilization and energy demand, is still being debated. There is, however, much circumstantial evidence, that supports the latter role of CK including the distinct, isoenzyme-specific subcellular localization of CK isoenzymes, the isolation and characterization of functionally coupled in vitro microcompartments of CK with a variety of cellular ATPases, and the observed functional coupling of mitochondrial oxidative phosphorylation with mitochondrial CK. New insight concerning the functions of the CK/PCr-system has been gained from recent M-CK null-mutant transgenic mice and by the investigation of CK localization and function in certain highly specialized non-muscle tissues and cells, such as electrocytes, retina photoreceptor cells, brain cells, kidney, salt glands, myometrium, placenta, pancreas, thymus, thyroid, intestinal brush-border epithelial cells, endothelial cells, cartilage and bone cells, macrophages, blood platelets, tumor and cancer cells. Studies with electric organ, including in vivo 31P-NMR, clearly reveal the buffer function of the CK/PCr-system in electrocytes and additionally corroborate a direct functional coupling of membrane-bound CK to the Na+/K(+)-ATPase. On the other hand, experiments with live sperm and recent in vivo 31P-NMR measurements on brain provide convincing evidence for the transport function of the CK/PCr-system. We report on new findings concerning the isoenzyme-specific cellular localization and subcellular compartmentation of CK isoenzymes in photoreceptor cells, in glial and neuronal cells of the cerebellum and in spermatozoa. Finally, the regulation of CK expression by hormones is discussed, and new developments concerning a connection of CK with malignancy and cancer are illuminated. Most interesting in this respect is the observed upregulation of CK expression by adenoviral oncogenes.