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

Placenta: an organ with high energy requirements

Placenta is a unique organ, without which the very phenomenon of human pregnancy is impossible. Semiallogeneous nature, localization of the placenta, complex and heterogeneous cellular composition determines its complex and multifaceted role in the course of physiological pregnancy, indicates the importance of studying this organ in a number of reproductive pathologies. The purpose of this review was to analyze the literature sources illustrating the importance of energydependent processes in placental metabolism and to determine the molecular basis of placental energy conversion. Publications of foreign and Russian authors from PubMed database and scientific electronic library eLIBRARY.ru were used when writing the review. The review highlights the main functions of the placenta: transport and synthetic functions in terms of their place in the structure of energy expenditure of the organ. The systems by which the transport of ions and gases from maternal blood through the placental barrier is performed, are considered. The role of the placenta in the synthesis of steroid hormones and glucocorticoids is detailed. The main bioenergetic systems are also considered: placental glucose metabolism, the functional activity of mitochondria and the creatine kinase system of the placenta. These data allow us to put the placenta on a par with other organs with high energy requirements (brain, transverse striated skeletal muscles, heart, kidneys, liver), which are most susceptible to metabolic disorders. Maintaining a balance between expenditure and synthesis of macroergic compounds in the placenta is critical for an adequate course of physiological pregnancy, and imbalances can lead to such pathologies as fetal retardation syndrome or preeclampsia. Further study of placental energy supply systems seems important for understanding the mechanisms of intrauterine development disorders and developing their pathogenetic treatment.

Creatine metabolism: energy homeostasis, immunity and cancer biology

Perturbations in metabolic processes are associated with diseases such as obesity, type 2 diabetes mellitus, certain infections and some cancers. A resurgence of interest in creatine biology is developing, with new insights into a diverse set of regulatory functions for creatine. This resurgence is primarily driven by technological advances in genetic engineering and metabolism as well as by the realization that this metabolite has key roles in cells beyond the muscle and brain. Herein, we highlight the latest advances in creatine biology in tissues and cell types that have historically received little attention in the field. In adipose tissue, creatine controls thermogenic respiration and loss of this metabolite impairs whole-body energy expenditure, leading to obesity. We also cover the various roles that creatine metabolism has in cancer cell survival and the function of the immune system. Renewed interest in this area has begun to showcase the therapeutic potential that lies in understanding how changes in creatine metabolism lead to metabolic disease.

Structure and function of resistance arteries from BB-creatine kinase and ubiquitous Mt-creatine kinase double knockout mice

Increasing evidence indicates that the enzyme creatine kinase (CK) is intimately involved in microvascular contractility. The mitochondrial isoenzyme catalyses phosphocreatine synthesis from ATP, while cytoplasmic CK, predominantly the BB isoenzyme in vascular tissue, is tightly bound near myosin ATPase, where it favours ATP production from phosphocreatine to metabolically support vascular contractility. However, the effect of CK gene inactivation on microvascular function is hitherto unknown. We studied functional and structural parameters of mesenteric resistance arteries isolated from 5 adult male mice lacking cytoplasmic BB-CK and ubiquitous mitochondrial CK (CK-/-) vs 6 sex/age-matched controls. Using a Mulvany Halpern myograph, we assessed the acute maximum contractile force with 125 mM K⁺ and 10^-5 M norepinephrine, and the effect of two inhibitors, dinitrofluorobenzene, which inhibits phosphotransfer enzymes (0.1 μM), and the specific adenylate kinase inhibitor P1, P5-di(adenosine 5') pentaphosphate (10^-6 to 10^-5 M). WT and CK-/- did not significantly differ in media thickness, vascular elasticity parameters, or acute maximum contractile force. CK-/- arteries displayed greater reduction in contractility after dinitrofluorobenzene 38%; vs 14% in WT; and after AK inhibition, 14% vs 5.5% in WT, and displayed abnormal mitochondria, with a partial loss of the inner membrane. Thus, CK-/- mice display a surprisingly mild phenotype in vascular dysfunction. However, the mitochondrial abnormalities and greater effect of inhibitors on contractility may reflect a compromised energy metabolism. In CK-/- mice, compensatory mechanisms salvage energy metabolism, as described for other CK knock-out models.

Organization of the gene for an invertebrate mitochondrial creatine kinase: comparisons with genes of higher forms and correlation of exon boundaries with functional domains

Two major gene duplication events are thought to have taken place in the evolution of creatine kinases (CK) in the vertebrates - (1) the formation of distinct mitochondrial (MiCK) and cytoplasmic forms from the primordial gene and (2) subsequent formation of the sarcomeric (sar-) and ubiquitous (ubi-) isoforms of octameric MiCK and muscle (M) and brain (B) isoforms of dimeric, cytoplasmic CK. The genes of these two CK clades reflect a distant divergence as sar- and ubiMiCK genes consistently have nine protein-coding exons while M- and B-CK genes have seven protein-coding exons; these genes share only one common exon. CKs are also widely distributed in the invertebrates and it has recently been shown that MiCKs evolved well before the divergence of the major metazoan groups. In the present communication, we report the structure and topology of the gene for MiCK from the protostome marine worm Chaetopterus variopedatus. The protein-coding region of the gene for this primitive MiCK spans over 10 kb and consists of eight exons, the last five (E4-E8) have identical boundaries to the corresponding exons of sar- and ubiMiCK genes. Exon-3 of the C. variopedatus MiCK gene consists of the corresponding E3 and E4 of the vertebrate MiCKs with no intervening intron. E1 is longer and E2 is shorter in the polychaete MiCK gene than the counterpart sarcomeric and ubiquitous genes. The insertion of the intron in C. variopedatus E3 creating the two exons as well as the rearrangement of the intron between E1 and E2 must have occurred prior to or coincident with the duplication event creating the two vertebrate mitochondrial isoforms. Sarcomeric and ubiMiCKs display substantial differences from their invertebrate MiCK counterparts in properties relating to octamer stability and membrane binding. The evolutionary changes in gene topology may be a component of this functional progression.

Initiating ocular proteomics for cataloging bovine retinal proteins: microanalytical techniques permit the identification of proteins derived from a novel photoreceptor preparation

Though some mechanisms of photoreception have been well characterized, others remain obscure. Presumably, most, if not all, of the major players in photoreceptor-specific functions are present in large amounts in the photoreceptor layer, and a catalog of these proteins will prove a useful tool for vision researchers. As a first step toward a complete catalog of photoreceptor cells, we have developed a novel method for isolating the photoreceptor cell monolayer from bovine retina. Electron microscopic studies of both the photoreceptor layer and the residual retina from which the photoreceptor layer had been removed, indicate that the preparation contains the photoreceptor outer segments and the majority of the inner segments. Proteins were extracted from the isolated photoreceptor cell layer as well as the rest of the retina with isoelectric focusing lysis buffer, and the protein components were separated by two-dimensional gel electrophoresis. The obtained protein maps reveal several classes of proteins that appear to be expressed more abundantly or specifically in the photoreceptor layer than in the rest of the retina. Four of these protein spots were excised and in-gel digested with trypsin, and the digests were extracted with solvent. The mixture of peptides digested from each protein was analyzed by high performance liquid chromatography interfaced with electrospray ionization tandem quadrupole mass spectrometry or by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Some of the peptides were isolated and their sequences were determined by gas phase Edman degradation. RNA transcripts extracted from the photoreceptor layer or the whole retina were subjected to Northern blot analysis as well as to reverse transcriptase-polymerase chain reaction amplification of probes for the successful selection of cDNA clones. These data permit both the identification of virtually any protein detectable on a two-dimensional gel, and also enable the corresponding cDNA clone to be selected. We have validated this approach by identifying aspartate aminotransferase and creatine kinase from the populations of abundant photoreceptor layer proteins. Both aspartate aminotransferase and creatine kinase are of mitochondrial origin and are thought to play crucial roles in photoreceptor functions by producing glutamate and ATP, respectively. We also identified two photoreceptor layer specific proteins: an acidic and high molecular weight protein, interphotoreceptor retinoid-binding protein, and an acidic and small molecular weight protein, recoverin.The technique presented here will allow vision researchers to discover and identify the proteins that are expressed specifically or abundantly in the photoreceptor cell as well as the proteins that undergo post-translational modification or modulation in expression under a defined biological condition. With the use of this technology, we anticipate that a researcher who knows only the 2-D gel position of a protein of interest can identify the protein, isolate a cDNA clone, and move into molecular genetic studies. Moreover, this streamlined technology will enable one to assemble a catalog of photoreceptor proteins using a minute amount of materials in a short period of time. We believe that such a catalog will serve as a valuable resource for vision investigators and will accelerate the rate of research progress.

Use of gene targeting for compromising energy homeostasis in neuro-muscular tissues: the role of sarcomeric mitochondrial creatine kinase

We have introduced a single knock-out mutation in the mitochondrial creatine kinase gene (ScCKmit) in the mouse germ line via targeted mutagenesis in mouse embryonic stem (ES) cells. Surprisingly, ScCKmit -/- muscles, unlike muscles of mice with a deficiency of cytosolic M-type creatine kinase (M-CK -/-; Van Deursen et al. (1993) Cell 74, 621-631), display no altered morphology, performance or oxidative phosphorylation capacity. Also, the levels of high energy phosphate metabolites were essentially unaltered in ScCKmit mutants. Our results challenge some of the present concepts about the strict coupling between CKmit function and aerobic respiration.

Evolution of the creative kinases. The chicken acidic type mitochondrial creatine kinase gene as the first nonmammalian gene

In both mammals and birds, the creatine kinase (CK) family consists of four types of genes: cytosolic brain type (B-CK); cytosolic muscle type (M-CK); mitochondrial ubiquitous, acidic type (Mia-CK); and mitochondrial sarcomeric, basic type (Mib-CK). We report here the cloning of the chicken Mia-CK cDNA and its gene. Amino acid sequences of the mature chicken Mi-CK proteins show about 90% identity to the homologous mammalian isoforms. The leader peptides, however, which are isoenzyme-specifically conserved among the mammalian Mi-CKs, are quite different in the chicken with amino acid identity values compared with the mammalian leader peptides of 38.5-51.3%. The chicken Mia-CK gene spans about 7.6 kilobases and contains 9 exons. The region around exon 1 shows a peculiar base composition, with more than 80% GC, and has the characteristics of a CpG island. The upstream sequences lack TATA or CCAAT boxes and display further properties of housekeeping genes. Several transcription factor binding sites known from mammalian Mi-CK genes are absent from the chicken gene. Although the promoter structure suggests a ubiquitous range of expression, analysis of Mia-CK transcripts in chicken tissues shows a restricted pattern and therefore does not fulfill all criteria of a housekeeping enzyme.