Developmental regulation of creatine kinase activity in cells of the epiphyseal growth cartilage

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.

Exercise training, creatine supplementation, and bone health in ovariectomized rats

Evidence suggests that creatine may have some beneficial effects on bone. The study aimed to investigate the effects of exercise alone or combined with creatine on bone health in ovariectomized rats. Findings show that exercise, but not creatine, has an important role in improving bone health.

INTRODUCTION

The aim of this study was to investigate the effects of exercise training alone or combined with creatine supplementation on bone health parameters in ovariectomized rats.

METHODS

Wistar rats were randomly allocated into one of five groups: (i) sham-operated, (ii) ovariectomized non-trained placebo-supplemented, (iii) ovariectomized non-trained creatine-supplemented, (iv) ovariectomized exercise-trained placebo-supplemented, and (v) ovariectomized exercise-trained creatine-supplemented. Downhill running training and/or creatine supplementation (300 mg/kg body weight) were administered for 12 weeks. Bone mineral content (BMC), bone mineral density (BMD), and biomechanical and histomorphometric parameters were assessed.

RESULTS

No interaction effects were observed for BMC and BMD at whole body, femur, and lumbar spine (p > 0.05). Importantly, a main effect of training was detected for whole body BMC and BMD (p = 0.003 and p < 0.001, respectively), femoral BMC and BMD (p = 0.005 and p < 0.001, respectively), and lumbar spine BMC and BMD (p < 0.001 and p < 0.001, respectively), suggesting that the trained animals had higher bone mass, irrespective of creatine supplementation. Main effects of training were also observed for maximal load (p < 0.001), stiffness (p < 0.001), and toughness (p = 0.046), indicating beneficial effects of exercise training on bone strength. Neither a main effect of supplementation nor an interaction effect was detected for biomechanical parameters (p > 0.05). No main or interaction effects were observed for any of the histomorphometric parameters evaluated (p > 0.05).

CONCLUSIONS

Exercise training, but not creatine supplementation, attenuated ovariectomy-induced bone loss in this rat model.

Active creatine kinase is present in matrix vesicles isolated from femurs of chicken embryo: Implications for bone mineralization

Proteomic analysis of matrix vesicles (MVs) isolated from 17-day-old chicken embryo femurs revealed the presence of creatine kinase. In this report we identified the enzyme functionally and suggest that the enzyme may participate in the synthesis of ATP from ADP and phosphocreatine within the lumen of these organelles. Then, ATP is converted by nucleotide hydrolyzing enzymes such as Na(+), K(+)-ATPase, protein kinase C, or alkaline phosphatase to yield inorganic phosphate (P(i)), a substrate for mineralization. Alternatively, ATP can be hydrolyzed by a nucleoside triphosphate pyrophosphatase phosphodiesterase 1 producing inorganic pyrophosphate (PP(i)), a mineralization inhibitor. In addition, immunochemical evidence indicated that VDAC 2 is present in MVs that may serve as a transporter of nucleotides from the extracellular matrix. We discussed the implications of ATP production and hydrolysis by MVs as regulatory mechanisms for mineralization.

Evidence for overgrowth after midfemoral fracture via increased RNA for mitosis

Middiaphyseal femoral fractures in children and young rats stimulate linear femoral growth, a phenomenon commonly attributed to increased vascularity. To test for changes in mRNA expression of genes related to blood vessels, nerve fibers, cartilage, bone, and cell metabolism, we measured mRNA gene expression for all known rat genes in the physis at various times after diaphyseal fracture. Female Sprague-Dawley rats, 4 weeks of age at surgery, were subjected to a unilateral, simple, transverse, middiaphyseal femoral fracture stabilized with an intramedullary rod. At 0 (intact), 0.1, 0.4, 1, 2, 3, 4, and 6 weeks after fracture, the femoral head with the proximal physis was collected from fractured and intact femora. The RNA was extracted, processed to biotinlabeled cRNA, and hybridized to Affymetrix Rat 230 2.0 GeneChip microarrays. Transcripts from fracture-induced lengthening of the injured femora were compared to those of the intact contralateral femur. In the proximal physis, transcripts related to blood vessels and cartilage formation were down-regulated by fracture. Transcripts related to bone remodeling, nerve axon elongation, cell division, and protein synthesis were up-regulated by fracture. The data support increased mitotic activity in the physis after a midshaft fracture and not increased vascularity.

Immunolocalization of heat shock protein 27 in developing jaw bones and tooth germs of human fetuses

27 kDa Heat shock protein (Hsp27), which is also identified as p29 estrogen-receptor associated protein, plays a crucial role in specific growth stages. It also seems to be involved in the balance between differentiation and apoptosis. To determine whether Hsp27 is involved during craniofacial development and odontogenesis, its expression was studied through immunohistochemistry of developing jaw bone as well as the odontogenesis of heads from human fetuses. Formalin-fixed paraffin-embedded specimens of 7 human fetuses (3 female, 4 male), obtained from miscarriages occurring between the 9th and 16th weeks of pregnancy, were examined by using a monoclonal antibody against Hsp27. Staining intensity (weak, +; moderate, ++; strong, +++) was evaluated semiquantitatively. The sample slice was cut through a coronal plane, which included eyes, nasal cavities, tongue, and primitive dental lamina with tooth germs. A transient and spatially restricted expression of Hsp27 in developing human jaw bones and teeth was observed. Osteoblasts around the uncalcified bone matrix showed Hsp27 immunoreaction products (+++), whereas osteocytes were not immunolabeled. In mandibular condyle, immunolabeling was restricted to hypertrophic chondrocytes (++). In developing tooth germs, Hsp27 immunostaining was detected throughout the bud (+++). At the early cap stage, a strong immunolabeling for Hsp27 was seen in the dental lamina (+++), and a moderate staining was seen in the outer dental epithelium (++). At the late cap stage, Hsp27 expression was detected in the outer dental epithelium (++) as well as in the cells of the future stellate reticulum (++). The spatiotemporal-restricted expression of Hsp27 in craniofacial bones during development suggests that this protein could be involved in the balance between differentiation and apoptosis, by modulating the viability of osteoblasts and chondrocytes. The specific regional and temporal expression patterns of Hsp27 during tooth development sustains that this small Hsp might be related to the morphogenesis and cytodifferentiation processes of tooth germs.

Selective anabolic effects of muteins of mid-region PTH fragments on skeletal tissues of prepubertal rats

We have demonstrated the net anabolic potential of a mid-region fragment of human parathyroid hormone (hPTH), and a protease resistant mutein derived from it, to stimulate growth of skeletal-derived tissues. The fragment hPTH (28-48), lacking the N-terminal amino acids necessary for stimulation of adenylate cyclase, and therefore unable to stimulate bone resorption by osteoclasts, was compared with the protease-resistant double-mutein hPTH (28-48) F34M L37T, full-length hPTH (1-84), the protease resistant form hPTH (1-84) L37T, 17beta estradiol (E(2)), and the combination of mid-region fragments of PTH and E(2). The hormones, at concentrations spanning a 100-fold range, were given by 14 injections (6/week, excluding Saturday), to 17-day-old female Wistar-derived rats. At the low concentration of 200 ng/day of PTH (1-84), or the molar equivalent of the fragment, and 50 ng E(2), all the hormones increased significantly the specific activity of creatine kinase (CK; a marker of skeletal cell proliferation) in tibial diaphysis and epiphysis, the width of the cortical bone in the humeral diaphysis, and the number of cells in the proliferating zone of the humeral epiphyseal growth plate. At a 10-fold lower concentration of both PTH and E(2), CK specific activity was synergistically stimulated in both diaphyseal bone and epiphyseal cartilage. However, PTH mid-region fragments at a dose of 1 microg/day did not increase trabecular bone volume.

Serum creatine kinase isoenzyme BB in mammalian osteopetrosis

In mammalian osteopetrosis the different mutations exemplify reduced bone resorption leading to net accumulation of bone. Recently, high blood levels of creatine kinase-BB have been reported in some human forms, suggesting it as a marker of osteopetrosis. In the current study serum creatine kinase-BB was evaluated in relation to known osteoclastic pathophysiology in two human types of autosomal dominant osteopetrosis at baseline and after stimulation with triiodothyronine and in four different rodent mutations. Creatine kinase-BB was increased markedly in Type 2 autosomal dominant osteopetrosis and in the incisors absent rat, both characterized by large numbers of giant osteoclasts, and did not change significantly after stimulation. Although creatine kinase-BB was unchanged in Type 1 autosomal dominant osteopetrosis at baseline and after stimulation, the rodent counterparts characterized by small osteoclasts, microphthalmic and osteopetrotic mice and toothless rats, had significantly decreased levels. Similar differences were observed in both types of autosomal dominant osteopetrosis compared with controls concerning tartrate resistant acid phosphatase. Creatine kinase-BB in mammalian osteopetrosis is related to osteoclastic number and size, where it probably reflects the differentiation and maturation of inactive bone resorbing cells. The isoenzyme does not seem to be a valuable screening marker for osteopetrosis.

Developmental expression of creatine kinase isoenzymes in chicken growth cartilage

We have shown previously that creatine kinase (CK) activity is required for normal development and mineralization of chicken growth cartilage and that expression of the cytosolic isoforms of CK is related to the biosynthetic and energy status of the chondrocyte. In this study, we have characterized changes in isoenzyme activity and mRNA levels of CK (muscle-specific CK, M-CK; brain-type CK, B-CK; and mitochondrial CK subunits, MiaCK and MibCK) in the growth plate in situ and in chondrocyte culture systems that model the development/maturation program of the cartilage. The in vitro culture systems analyzed were as follows: tibial chondrocytes, which undergo hypertrophy; embryonic cephalic and caudal sternal chondrocytes, which differ from each other in their mineralization response to retinoic acid; and long-term micromass cultures of embryonic limb mesenchymal cells, which recapitulate the chondrocyte differentiation program. In all systems analyzed, B-CK was found to be the predominant isoform. In the growth plate, B-CK expression was highest in the most calcified regions, and M-CK was less abundant than B-CK in all regions of the growth plate. In tibial chondrocytes, an increase in B-CK expression was seen when the cells became hypertrophic. Expression of B-CK increased slightly over 15 days in mineralizing, retinoic acid-treated cephalic chondrocytes, but it decreased in nonmineralizing caudal chondrocytes, while there was little expression of M-CK. Interestingly, in limb mesenchyme cultures, significant M-CK expression was detected during chondrogenesis (days 2-7), whereas hypertrophic cells expressed only B-CK. Finally, expression of MiaCK and MibCK was low both in situ and in vitro. These observations suggest that the CK genes are differentially regulated during cartilage development and maturation and that an increase in CK expression is important in initiating chondrocyte maturation.

Creatine kinase brain isoenzyme (BB-CK) presence in serum distinguishes osteopetroses among the sclerosing bone disorders

Creatine kinase (CK) isoenzyme BB-CK is predominantly found in brain and is not normally detected in the blood. A few recent reports, however, have described BB-CK in serum from several patients with osteopetrosis (OP). To evaluate the presence and specificity of BB-CK in serum in the osteopetroses among disorders that increase skeletal mass, we quantitated total CK activity and CK isoenzymes in 15 patients representing the five major clinical forms of OP (2 infantile, 3 intermediate, 7 adult [2 type I, 5 type II], and 3 carbonic anhydrase II [CA II] deficiency cases) and in 22 patients representing 14 other types of sclerosing bone disease. All OP patients (except the two adult type I subjects) had BB-CK readily detected in their serum. Conversely, only 1 of the 22 patients with other sclerosing bone disorders had detectable BB-CK in serum (1 of 3 patients with fibrodysplasia [myositis] ossificans progressiva who had barely measurable activity). In three OP patients (one of two with the infantile form and two of five with adult, type II disease), BB-CK values were sufficiently high that serum total CK activity was elevated. In a newborn with malignant OP, both cord blood plasma and peripheral blood serum had substantial amounts of BB-CK. In three subjects (with adult type II OP), who were restudied 2-6 years later, BB-CK was still elevated in their blood. BB-CK in serum appears to distinguish the osteopetroses among the sclerosing bone disorders. Absence of serum BB-CK in adult type I disease suggests that this condition may not be a genuine form of OP. Assay of BB-CK in fetal blood could be studied as a means for prenatal diagnosis of malignant OP. Why the osteoclast failure that characterizes all true forms of OP is associated with BB-CK in the circulation is a new question for skeletal biologists.

Adaptation of chondrocytes to low oxygen tension: relationship between hypoxia and cellular metabolism

In endochondral bone, the growth cartilage is the site of rapid growth. Since the vascular supply to the cartilage is limited, it is widely assumed that cells of the cartilage are hypoxic and that limitations in the oxygen supply regulate the energetic state of the maturing cells. In this report, we evaluate the effects of oxygen tension on chondrocyte energy metabolism, thiol status, and expression of transcription elements, HIF and AP-1. Imposition of an hypoxic environment on cultured chondrocytes caused a proportional increase in glucose utilization and elevated levels of lactate synthesis. Although we observed a statistical increase in the activities of phosphofructokinase, pyruvate kinase, lactate dehydrogenase, and creatine kinase after exposure to lowered oxygen concentrations, the effect was small. The cultured cells exhibited a decreased utilization of glutamine, possibly due to down regulation of mitochondrial function and inhibition of oxidative deamination. With respect to total energy generation, we noted that these cells are quite capable of maintaining the energy charge of the cell at low oxygen tensions. Indeed, no changes in the absolute quantity of adenine nucleotides or the energy charge ratio was observed. Hypoxia caused a decrease in the glutathione content of cultured chondrocytes and a concomitant rise in cell and medium cysteine levels. It is likely that the fall in cell glutathione level is due to decreased synthesis of the tripeptide under reduced oxygen stress and the limited supply of glutamate. The observed rise in cellular and medium cysteine levels probably reflects an increase in the rate of degradation of glutathione and a decrease in synthesis of the peptide. To explore how cells transduce these metabolic effects, gel retardation assays were used to study chondrocyte HIF and AP-1 binding activities. Chondrocyte nuclear preparations bound an HIF-oligonucleotide; however, at low oxygen tensions, no increase in HIF binding was observed. In addition, we found that AP-1 binding activities in chondrocytes exposed to low oxygen tensions was elevated, although the response was lower than that exhibited by fibroblasts exposed to the same range of oxygen concentrations. We compared these results to HIF and AP-1 binding by cells in the growth plate. There was strong HIF and AP-1 binding throughout the plate, but no evidence of selective binding to any one zone. The results of the study lend strong support to the view that chondrocytes are very well adapted to low oxygen tensions; thus, under hypoxic conditions, there is a high level of expression of both HIF and AP-1, and energy conservation appears to be near-maximum.

Enzymes in mineralizing systems: state of the art

The hallmark of biological mineralization is the precise regulation of mineral deposition in space and time. The cells which produce mineralized tissues are themselves controlled by developmental programs and hormonal signals which result in regulation of gene expression and modulation of protein function. These signals are transduced into changes in enzyme levels and/or activity. Upon activation, cellular enzymes then act to synthesize the organic matrix and process it extracellularly, utilize metabolic energy to transport ions from the blood to the matrix, and to initiate the mineralization cascade. The first enzyme activity described in mineralizing tissues was alkaline phosphatase and it is still the best characterized enzyme in the mineralization process. Yet, important questions about the role of this protein remain unanswered, and it continues to occupy a central focus in mineralized tissue investigation. Other phosphatases, including protein tyrosine phosphatases are important in regulating tyrosine kinase mediated signals. Investigators have now begun to look closely at several groups of kinases which are also important for proper mineralization. As peptide hormones are important modulators of mineralized tissues, protein kinase A has always been presumed to play a key role in phosphorylating intracellular proteins. There is also considerable interest in protein kinase C, as well as tyrosine kinases in mineralized tissue signal transduction. Another group of kinases important in mineralized tissues are the enzymes which phosphorylate the matrix phosphoproteins. Of these, casein kinase II appears to be involved in intracellular and extracellular protein phosphorylation. Several enzymes present in the premineralized matrix are thought to be significant in triggering mineralization. Alkaline phosphatase may act at this level, but new data also suggests that metalloproteases and gelatinases, by modifying or digesting matrix components, may be important in the initiation of calcification.

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.

Adenosine 5'-triphosphate promotes mineralization in differentiating chick limb-bud mesenchymal cell cultures

When chick limb-bud mesenchymal cells are plated in micromass culture, they differentiate to form a mineralizable cartilage matrix. Previous studies have demonstrated that, when the total inorganic phosphate concentration of the medium is adjusted to 3-4 mM by adding inorganic phosphate to the basal medium, the mineralized matrix formed resembles that of chick calcified cartilage in ovo. When the high-energy phosphates adenosine 5'-triphosphate (ATP) or creatine phosphate are used as supplements in place of inorganic phosphate, the mineralized matrix as analyzed by electron microscopy and Fourier transform infrared microscopy is also similar to that in ovo. This is in marked contrast to the mineralized matrix formed in the presence of 2.5-5 mM beta-glycerophosphate, where mineral deposition is random and mineral crystal sizes in general are larger. This is also in contrast to the known ability of ATP to inhibit mineral deposition in solution in the absence of cells. In the differentiating mesenchymal cell culture system, ATP does not alter the rate of cell proliferation (DNA content), the rate of matrix synthesis (3H-leucine uptake), the mean crystallite length, or the rate of mineral deposition (45Ca uptake) when contrasted with cultures supplemented with inorganic phosphate. However, ATP does increase the mineral to matrix ratio, especially around the edge of the culture, where a type I collagen matrix is presented. It is suggested that ATP promotes mineral deposition by providing a high-energy phosphate source, which may be used to phosphorylate extracellular matrix proteins and to regulate calcium flux through cell membranes.

Retinoic acid induces a shift in the energetic state of hypertrophic chondrocytes

In the epiphyseal growth plate, chondrocyte maturation is accompanied by dramatic alterations in energy metabolism. To explore the relationship between these two events, we used retinoic acid (RA) to promote chondrocyte maturation in culture. The specific question that was addressed was, does RA treatment of cultured chondrocytes in vitro induce a change in energy status similar to that seen in hypertrophic chondrocytes in vivo. Maturing chondrocytes isolated from the cephalic region of day 18 chick embryo sterna were allowed to grow for 7-14 days in monolayer until confluent and then treated with 10-300 nM RA. Immature chondrocytes from the caudal region of sternum were grown in parallel and served as control cells for the study. We found that in maturing cephalic cell cultures, RA had a rapid and profound effect on oxidative metabolism. The retinoid caused a reduction in the energy charge ratio (ECR) and the ATP/ADP ratio and a sharp decrease in cell ATP levels. Maximum inhibition was observed when the RA concentration was 10-35 nM. Compared with the adenine nucleotides, creatine phosphate levels were decreased to a lesser extent by RA, although there was substantial inhibition of creatine kinase activity. We expected to find a compensatory elevation in glycolytic activities; however, the lactate levels in the medium of the treated cells indicated that anaerobic glycolysis was depressed. In contrast to the cephalic chondrocytes, when caudal cell cultures were treated with RA, lactate formation was stimulated and there were minimal effects on oxidative metabolism. To determine the mechanism of inhibition of glycolysis, we measured the activity of pyruvate kinase in RA-treated cephalic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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.