Crystalline mitochondrial inclusion bodies isolated from creatine depleted rat soleus muscle

Educational Case: Mitochondrial Myopathy

The following fictional case is intended as a learning tool within the Pathology Competencies for Medical Education (PCME), a set of national standards for teaching pathology. These are divided into three basic competencies: Disease Mechanisms and Processes, Organ System Pathology, and Diagnostic Medicine and Therapeutic Pathology. For additional information, and a full list of learning objectives for all three competencies, see http://journals.sagepub.com/doi/10.1177/2374289517715040.¹

Giant crystals inside mitochondria of equine chondrocytes

The present study reports for the first time the presence of giant crystals in mitochondria of equine chondrocytes. These structures show dark contrast in TEM images as well as a granular substructure of regularly aligned 1-2 nm small units. Different zone axes of the crystalline structure were analysed by means of Fourier transformation of lattice-resolution TEM images proving the crystalline nature of the structure. Elemental analysis reveals a high content of nitrogen referring to protein. The outer shape of the crystals is geometrical with an up to hexagonal profile in cross sections. It is elongated, spanning a length of several micrometres through the whole cell. In some chondrocytes, several crystals were found, sometimes combined in a single mitochondrion. Crystals were preferentially aligned along the long axis of the cells, thus appearing in the same orientation as the chondrocytes in the tissue. Although no similar structures have been found in the cartilage of any other species investigated, they have been found in cartilage repair tissue formed within a mechanically stimulated equine chondrocyte construct. Crystals were mainly located in superficial regions of cartilage, especially in joint regions of well-developed superficial layers, more often in yearlings than in adult horses. These results indicate that intramitochondrial crystals are related to the high mechanical stress in the horse joint and potentially also to the increased metabolic activity of immature individuals.

Protein "amyloid-like" networks at the phospholipid membrane formed by 4-hydroxy-2-nonenal-modified mitochondrial creatine kinase

4-Hydroxy-2-nonenal (4-HNE) is a reactive aldehyde and a lipid peroxidation product formed in biological tissues under physiological and pathological conditions. Its concentration increases with oxidative stress and induces deleterious modifications of proteins and membranes. Mitochondrial and cytosolic isoforms of creatine kinase were previously shown to be affected by 4-HNE. In the present study, we analyzed the effect of 4-HNE on mitochondrial creatine kinase, an abundant protein from the mitochondrial intermembrane space with a key role in mitochondrial physiology. We show that this effect is double: 4-HNE induces a step-wise loss of creatine kinase activity together with a fast protein aggregation. Protein-membrane interaction is affected and amyloid-like networks formed on the biomimetic membrane. These fibrils may disturb mitochondrial organisation both at the membrane and in the inter membrane space.

[Internal carotid artery dissection as a cause of severe ischemic stroke with lethal outcome]

We present a medical history of a 30-year old male patient with fatal ischemic stroke, resulting from the right internal carotid artery (ICA) dissection provoked by repeated head tilts and verified by magnetic resonance imaging and pathomorphological examination. At admission, the high level of creatine phosphokinase (5284 un/ml, normal level<171) in the blood was found, the coagulation parameters were normal. Autopsy revealed intramural hematoma (IMH), which was located between the media and adventitia of the arterial wall, began at 3 cm above the common carotid artery bifurcation and extended to the base of the skull. The lumen of the ICA at the level of the IMG and intracranial parts as well as of the middle cerebral artery was occluded by the thrombus. The histological examination of the right ICA wall found splitting, thinning, fragmentation, disrupters of internal elastic membrane, severe media fibrosis, myocyte necrosis at the site of the dissection with the surrounding leukocyte infiltration, as well as lymphocytic infiltrates, clusters of eosinophils in adventitia. Similar changes, except myocyte necrosis, were also found in intact (non-dissected) brain supplying arteries. In general, they were similar to those in fibromuscular dysplasia (FMD). Histochemical and electron microscopic studies of skeletal muscles showed signs of mitochondrial cytopathy. The authors discuss the relationship between the dissection, FMD and mitochondrial pathology.

Aldehyde dehydrogenase, Ald4p, is a major component of mitochondrial fluorescent inclusion bodies in the yeast Saccharomyces cerevisiae

When Saccharomyces cerevisiae strain 3626 was cultured to the stationary phase in a medium that contained glucose, needle-like structures that emitted autofluorescence were observed in almost all cells by fluorescence microscopy under UV excitation. The needle-like structures completely overlapped with the profile of straight elongated mitochondria. Therefore, these structures were designated as mitochondrial fluorescent inclusion bodies (MFIBs). The MFIB-enriched mitochondrial fractions were successfully isolated and 2D-gel electrophoresis revealed that a protein of 54 kDa was only highly concentrated in the fractions. Determination of the N-terminal amino acid sequence of the 54-kDa protein identified it as a mitochondrial aldehyde dehydrogenase, Ald4p. Immunofluorescence microscopy showed that anti-Ald4p antibody specifically stained MFIBs. Freeze-substitution electron microscopy demonstrated that cells that retained MFIBs had electron-dense filamentous structures with a diameter of 10 nm in straight elongated mitochondria. Immunoelectron microscopy showed that Ald4p was localized to the electron-dense filamentous structures in mitochondria. These results together showed that a major component of MFIBs is Ald4p. In addition, we demonstrate that MFIBs are common features that appear in mitochondria of many species of yeast.

The effect of the creatine analogue beta-guanidinopropionic acid on energy metabolism: a systematic review

Background

Creatine kinase plays a key role in cellular energy transport. The enzyme transfers high-energy phosphoryl groups from mitochondria to subcellular sites of ATP hydrolysis, where it buffers ADP concentration by catalyzing the reversible transfer of the high-energy phosphate moiety (P) between creatine and ADP. Cellular creatine uptake is competitively inhibited by beta-guanidinopropionic acid. This substance is marked as safe for human use, but the effects are unclear. Therefore, we systematically reviewed the effect of beta-guanidinopropionic acid on energy metabolism and function of tissues with high energy demands.

Methods

We performed a systematic review and searched the electronic databases Pubmed, EMBASE, the Cochrane Library, and LILACS from their inception through March 2011. Furthermore, we searched the internet and explored references from textbooks and reviews.

Results

After applying the inclusion criteria, we retrieved 131 publications, mainly considering the effect of chronic oral administration of beta-guanidinopropionic acid (0.5 to 3.5%) on skeletal muscle, the cardiovascular system, and brain tissue in animals. Beta-guanidinopropionic acid decreased intracellular creatine and phosphocreatine in all tissues studied. In skeletal muscle, this effect induced a shift from glycolytic to oxidative metabolism, increased cellular glucose uptake and increased fatigue tolerance. In heart tissue this shift to mitochondrial metabolism was less pronounced. Myocardial contractility was modestly reduced, including a decreased ventricular developed pressure, albeit with unchanged cardiac output. In brain tissue adaptations in energy metabolism resulted in enhanced ATP stability and survival during hypoxia.

Conclusion

Chronic beta-guanidinopropionic acid increases fatigue tolerance of skeletal muscle and survival during ischaemia in animal studies, with modestly reduced myocardial contractility. Because it is marked as safe for human use, there is a need for human data.

Disturbed energy metabolism and muscular dystrophy caused by pure creatine deficiency are reversible by creatine intake

Creatine (Cr) plays an important role in muscle energy homeostasis by its participation in the ATP-phosphocreatine phosphoryl exchange reaction mediated by creatine kinase. Given that the consequences of Cr depletion are incompletely understood, we assessed the morphological, metabolic and functional consequences of systemic depletion on skeletal muscle in a mouse model with deficiency of l-arginine:glycine amidinotransferase (AGAT(-/-)), which catalyses the first step of Cr biosynthesis. In vivo magnetic resonance spectroscopy showed a near-complete absence of Cr and phosphocreatine in resting hindlimb muscle of AGAT(-/-) mice. Compared with wild-type, the inorganic phosphate/β-ATP ratio was increased fourfold, while ATP levels were reduced by nearly half. Activities of proton-pumping respiratory chain enzymes were reduced, whereas F(1)F(0)-ATPase activity and overall mitochondrial content were increased. The Cr-deficient AGAT(-/-) mice had a reduced grip strength and suffered from severe muscle atrophy. Electron microscopy revealed increased amounts of intramyocellular lipid droplets and crystal formation within mitochondria of AGAT(-/-) muscle fibres. Ischaemia resulted in exacerbation of the decrease of pH and increased glycolytic ATP synthesis. Oral Cr administration led to rapid accumulation in skeletal muscle (faster than in brain) and reversed all the muscle abnormalities, revealing that the condition of the AGAT(-/-) mice can be switched between Cr deficient and normal simply by dietary manipulation. Systemic creatine depletion results in mitochondrial dysfunction and intracellular energy deficiency, as well as structural and physiological abnormalities. The consequences of AGAT deficiency are more pronounced than those of muscle-specific creatine kinase deficiency, which suggests a multifaceted involvement of creatine in muscle energy homeostasis in addition to its role in the phosphocreatine-creatine kinase system.

Effects of the anti-thyroidal compound potassium-perchlorate on the thyroid system of the zebrafish

The increasing pollution of aquatic habitats with anthropogenic compounds has led to various test strategies to detect hazardous chemicals. However, information on effects of pollutants in the thyroid system in fish, which is essential for growth, development and parts of reproduction, is still scarce. Other vertebrate groups such as amphibians or mammals are well-studied; so the need for further knowledge especially in fish as a favored vertebrate model test organism is evident. Modified early life-stage tests were carried out with zebrafish exposed to the known thyroid inhibitor potassium perchlorate (0, 62.5, 125, 250, 500 and 5000 μg/L) to identify adverse effects on the hypothalamic-pituitary-thyroid axis. Especially higher perchlorate concentrations led to conspicuous alterations in thyroidal tissue architecture and to effects in the pituitary. In the thyroid, severe hyperplasia at concentrations ≥ 500 μg/L together with an increase in follicle number could be detected. The most sensitive endpoint was the colloid, which showed alterations at ≥ 250 μg/L. The tinctorial properties and the texture of the colloid changed dramatically. Interestingly, effects on epithelial cell height were minor. The pituitary revealed significant proliferations of TSH-producing cells resulting in alterations in the ratio of adeno- to neurohypophysis. The liver as the main site of T4 deiodination showed severe glycogen depletion at concentrations ≥ 250 μg/L. In summary, the thyroid system in zebrafish showed effects by perchlorate from concentrations ≥ 250 μg/L, thus documenting a high sensitivity of the zebrafish thyroid gland for goitrogens. In the future, such distinct alterations could lead to a better understanding and identification of potential thyroid-disrupting chemicals.

X-linked creatine transporter deficiency presenting as a mitochondrial disorder

X-linked creatine transporter defect is caused by mutations in SLC6A8 at Xq28, which encodes the sodium-dependent creatine transporter. Reduction in creatine uptake results in elevated urine creatine and CSF creatine deficiency, which can be detected on magnetic resonance spectroscopy. We report a patient who was initially suspected of having a mitochondrial disorder but was later found to have a creatine transporter defect. The abnormal laboratory study results seen in this patient suggesting a mitochondrial cytopathy could be due to excess mitochondrial stress as well as the mitochondrial inclusion bodies. This report looks at the mitochondrial presentation of the creatine transporter deficiency.

Dynamic organization of mitochondria in human heart and in myocardial disease

Heart mitochondria, which, depending on their location within cardiomyofibers, are classified as either subsarcolemmal or interfibrillar, are the major sources of the high energy compound, adenosine triphosphate. Physiological differences between these two populations are reflected by differences in the morphology of their cristae, with those of subsarcolemmal mitochondria being mostly lamelliform, and those of interfibrillar mitochondria being mostly tubular. What determines the configuration of cristae, not only in cardiac mitochondria but in mitochondria in general, is unclear. The morphology of cardiac mitochondria, as well as their physiology, is responsive to the exigencies posed by a large variety of pathological situations. Giant cardiac mitochondria make an appearance in certain types of cardiomyopathy and as a result of dietary, pharmacological, and toxicological manipulation; such megamitochondria probably arise by a combination of fusion and true growth. Some of these enlarged organelles occasionally contain a membrane-bound deposit of beta-glycogen. Those giant mitochondria induced by experimental treatment usually can be restored to normal dimensions simply by supplying the missing nutrient or by deleting the noxious substance. In some conditions, such as endurance training and ischemia, the mitochondrial matrices become pale. Dense rods or plates are present in the outer compartment of mitochondria under certain conditions. Biochemical alterations in cardiac mitochondria appear to be important in heart failure. In aging, only interfibrillar mitochondria exhibit such changes, with the subsarcolemmal mitochondria unaffected. In certain heart afflictions, biochemical defects are not accompanied by obvious morphological transformations. Mitochondria clearly play a cardinal role in homeostasis of the heart.

Oncocytic adrenal cortical tumor with cytoplasmic inclusions and hyaline globules

Adrenal cortical tumors, particularly oncocytic tumors, have been reported to contain a variety of intracytoplasmic and intramitochondrial inclusions. Oncocytic cortical tumors can also morphologically mimic pheochromocytomas. We report an unusual, partially oncocytic cortical neoplasm with nesting architecture, intranuclear inclusions, and hyaline globules reminiscent of pheochromocytoma, together with numerous, small, brightly eosinophilic, periodic acid-Schiff-positive cytoplasmic inclusions and typical cytoplasmic lipid droplets. Ultrastructural study revealed oncocytes containing numerous mitochondria with intramitochondrial crystals and lipid droplets. Immunohistochemistry and immunoblots were utilized to further characterize the tumor. Immunohistochemistry demonstrated immunoreactivity of both the eosinophilic inclusions and the hyaline globules for adipose differentiation-related protein (ADRP), which is one of a group of proteins associated with storage of neutral lipids in many cell types. Immunoblots confirmed the presence of ADRP and demonstrated an imbalance between ADRP and perilipin, another neutral lipid-associated protein, in tumor tissue compared to normal adrenal cortex. The findings suggest that mitochondrial dysfunction in oncocytic cortical tumors may lead to abnormal processing of proteins related to the lipid-storing functions of the adrenal cortex, resulting in unusual cytoplasmic inclusions and extracellular globules resembling the globules in pheochromocytomas. The finding of ADRP as a constituent of inclusions in adrenal cortical tumors has not been previously reported.

Influence of constant positive airway pressure therapy on lipid storage, muscle metabolism and insulin action in obese patients with severe obstructive sleep apnoea syndrome

AIM

To observe the effect of constant positive airway pressure (CPAP) therapy on regional lipid deposition, muscle metabolism and glucose homeostasis in obese patients with obstructive sleep apnoea syndrome (OSAS).

METHODS

A total of 29 obese patients underwent assessment before and after a minimum of 12-week CPAP therapy. Abdominal adipose tissue was assessed using magnetic resonance imaging. Intramyocellular lipid (IMCL) and skeletal muscle creatine were assessed using (1)H-magnetic resonance spectroscopy. Fasting venous and arterial blood were collected. Glucose control was assessed using the homeostatic model. A subgroup of six patients were also evaluated for skeletal muscle pH, phosphocreatine (PCr) and mitochondrial function using (31)P-magnetic resonance spectroscopy. The sample was divided according to CPAP therapy, with regular users defined as a minimum nightly use of >or=4 h; 19 subjects were regular and 10 were irregular CPAP users.

RESULTS

Visceral adipose tissue volume and circulating leptin were reduced with regular CPAP use but not with irregular CPAP use. Regular CPAP use also produced an increase in skeletal muscle creatine and resting PCr and a decrease in muscle pH. Neither the regular nor irregular CPAP users showed any change in IMCL content, insulin sensitivity scores or mitochondrial function.

CONCLUSIONS

These data show that regular CPAP therapy reduces visceral adipose tissue and leptin and improves skeletal muscle metabolites. In obese patients with severe OSAS, regular CPAP use does not improve glucose control, suggesting that the influence of obesity on glucose control dominates over any potential effect of OSAS.

X-linked creatine transporter defect: a report on two unrelated boys with a severe clinical phenotype

We report two unrelated boys with the X-linked creatine transporter defect (CRTR) and clinical features more severe than those previously described with this disorder. These two boys presented at ages 12 and 30 months with severe mental retardation, absent speech development, hypotonia, myopathy and extra-pyramidal movement disorder. One boy has seizures and some dysmorphic features; he also has evidence of an oxidative phosphorylation defect. They both had classical absence of creatine peak on brain magnetic resonance spectroscopy (MRS). In one, however, this critical finding was overlooked in the initial interpretation and was discovered upon subsequent review of the MRS. Molecular studies showed large genomic deletions of a large part of the 3' end of the complete open reading frame of the SLC6A8 gene. This report emphasizes the importance of MRS in evaluating neurological symptoms, broadens the phenotypic spectrum of CRTR and adds knowledge about the pathogenesis of creatine depletion in the brain and retina.

Mitochondrial creatine kinase in human health and disease

Mitochondrial creatine kinase (MtCK), together with cytosolic creatine kinase isoenzymes and the highly diffusible CK reaction product, phosphocreatine, provide a temporal and spatial energy buffer to maintain cellular energy homeostasis. Mitochondrial proteolipid complexes containing MtCK form microcompartments that are involved in channeling energy in form of phosphocreatine rather than ATP into the cytosol. Under situations of compromised cellular energy state, which are often linked to ischemia, oxidative stress and calcium overload, two characteristics of mitochondrial creatine kinase are particularly relevant: its exquisite susceptibility to oxidative modifications and the compensatory up-regulation of its gene expression, in some cases leading to accumulation of crystalline MtCK inclusion bodies in mitochondria that are the clinical hallmarks for mitochondrial cytopathies. Both of these events may either impair or reinforce, respectively, the functions of mitochondrial MtCK complexes in cellular energy supply and protection of mitochondria form the so-called permeability transition leading to apoptosis or necrosis.

Octameric mitochondrial creatine kinase induces and stabilizes contact sites between the inner and outer membrane

We have investigated the role of the protein ubiquitous mitochondrial creatine kinase (uMtCK) in the formation and stabilization of inner and outer membrane contact sites. Using liver mitochondria isolated from transgenic mice, which, unlike control animals, express uMtCK in the liver, we found that the enzyme was associated with the mitochondrial membranes and, in addition, was located in membrane-coated matrix inclusions. In mitochondria isolated from uMtCK transgenic mice, the number of contact sites increased 3-fold compared with that observed in control mitochondria. Furthermore, uMtCK-containing mitochondria were more resistant to detergent-induced lysis than wild-type mitochondria. We conclude that octameric uMtCK induces the formation of mitochondrial contact sites, leading to membrane cross-linking and to an increased stability of the mitochondrial membrane architecture.

C-terminal Lysines Determine Phospholipid Interaction of Sarcomeric Mitochondrial Creatine Kinase

High affinity interaction between octameric mitochondrial creatine kinase (MtCK) and the phospholipid cardiolipin in the inner mitochondrial membrane plays an important role in metabolite channeling between MtCK and inner membrane adenylate translocator, which itself is tightly bound to cardiolipin. Three C-terminal basic residues revealed as putative cardiolipin anchors in the x-ray structures of MtCK and corresponding to lysines in human sarcomeric MtCK (sMtCK) were exchanged by in vitro mutagenesis (K369A/E, K379Q/A/E, K380Q/A/E) to yield double and triple mutants. sMtCK proteins were bacterially expressed, purified to homogeneity, and verified for structural integrity by enzymatic activity, gel filtration chromatography, and CD spectroscopy. Interaction with cardiolipin and other acidic phospholipids was quantitatively analyzed by light scattering, surface plasmon resonance, and fluorescence spectroscopy. All mutant sMtCKs showed a strong decrease in vesicle cross-linking, membrane affinity, binding capacity, membrane ordering capability, and binding-induced changes in protein structure as compared with wild type. These effects did not depend on the nature of the replacing amino acid but on the number of exchanged lysines. They were moderate for Lys-379/Lys-380 double mutants but pronounced for triple mutants, with a 30-fold lower membrane affinity and an entire lack of alterations in protein structure compared with wild-type sMtCK. However, even triple mutants partially maintained an increased order of cardiolipin-containing membranes. Thus, the three C-terminal lysines determine high affinity sMtCK/cardiolipin interaction and its effects on MtCK structure, whereas low level binding and some effect on membrane fluidity depend on other structural components. These results are discussed in regard to MtCK microcompartments and evolution.

Stimulation of HSP72 expression following ATP depletion and short-term exercise training in fast-twitch muscle

AIM

Previous data have reported increases in HSP72 expression in skeletal muscles after endurance training but the physiological and biochemical signals that induce HSP72 accumulation remain largely unknown. In this study, we tested the hypothesis that energy status is a key regulatory event for HSP72 accumulation in skeletal muscles.

METHODS

Reduction of high-energy phosphate levels was induced by supplementation with a creatine analogue, beta-guanidinopropionic acid (GPA) for 3 weeks while control rats received distilled water in the same conditions. Half of the animals were kept sedentary while the others were submitted to a short-term (2 weeks) training program on a treadmill (30 m min-1, 0% slope; 50-70 min day-1).

RESULTS

GPA supplementation resulted in a large drop ( approximately 50%) in adenosine triphosphate (ATP) level in both fast and slow muscles whether the animals were trained or remained sedentary. HSP72 level did not change with GPA alone, but the training-induced increase in HSP72 level was strongly enhanced by superimposition of GPA diet in fast but not in slow skeletal muscles. The changes in HSP72 level were not linked to changes in fibre typology and/or mitochondrial capacities.

CONCLUSIONS

The results of the present investigation indicate that levels of high-energy phosphate per se do not play a direct role in determining HSP72 level in skeletal muscles. However, during superimposition of training to GPA, then the adaptive strategy of fast-twitch muscle (e.g. plantaris) seems to be directed towards appearance of some properties of red, oxidative fibres (increase in oxidative capacities and HSP72 level).

Attenuation of free radical production and paracrystalline inclusions by creatine supplementation in a patient with a novel cytochrome b mutation

Mitochondrial cytopathies are associated with increased free radical generation and paracrystalline inclusions. Paracrystalline inclusions were serendipitously found in a young male athlete with a very high respiratory exchange ratio during steady-state exercise; he also had an unusually low aerobic capacity. Direct sequencing of the mitochondrial DNA (mtDNA) coding regions revealed a novel missense mutation (G15497A) resulting in a glycine-->serine conversion at a highly conserved site in the cytochrome b gene in the subject, his mother, and sister. Cybrids, prepared by fusion of the subject's platelets with either U87MG rho degrees or SH-SY5Y rho degrees cells, generated higher basal levels of reactive oxygen species (ROS), had a lower adenosine triphosphate (ATP) content, and were more sensitive to oxygen and glucose deprivation and peroxynitrite generation compared to control cybrids with wild-type mtDNA. Cell survival was significantly enhanced with 50 mmol/L creatine monohydrate (CM) administration. The subject was also treated with CM (10 g/d) for a period of 5 weeks and a repeat muscle biopsy showed no paracrystalline inclusions. The results suggest that the development of exercise-induced paracrystalline inclusions may be influenced by the G15497A mtDNA mutation, and that CM mitigates against the pathological consequences of this mutation.

Ergastoplasmic paracrystalline inclusion bodies in the adipose gonadal envelope and fat body of the glow worm, Lampyris noctiluca (Insecta, Coleoptera)

The gonads of glow worm larvae are enveloped by adipose tissue which represents a specialized fat body. The adipose gonadal envelope, and also to a lesser extent the fat body cells, contain tubular paracrystalline inclusion bodies (PIBs). Cells of other tissues are devoid of such inclusions. The PIBs form in the cisternae of rough ER. In young larvae PIB formation is sparse, but at advanced larval stages PIBs often occur as bundles in stacks of ergastoplasm. Typically, a PIB within a cisterna consists of four to seven parallel tubules. The outer diameter of a tubule is ca 28.8 nm and the width of the tubule lumen ca 12.2 nm. The "wall" of a tubule contains globular protein subunits of ca 8.3 nm diameter; the subunits are arranged helically. Since the adipose gonadal envelope progresses through a cytological differentiation process during differentiation and maturation of the gonads, the increased number of PIBs may indicate enhanced metabolic activity of the tissue related to nutrition of the growing gonads.

Neuronal plasticity and stressor toxicity during aging

Brain aging, Alzheimer disease and stroke share common elements of deficits in calcium regulation, declines in mitochondrial function, increases in generation of reactive oxygen species (ROS), accumulated damage from ROS and immune system dysfunction. The problem is to distinguish less significant side reactions, such as gray hair, from aspects of aging that contribute to disease. Toward establishing cause and effect relationships, a neuron cell culture system is described that allows comparisons with age under uniform environmental conditions. This neuron culture model indicates that susceptibility to death by apoptosis and consequences of the inflammatory response from beta-amyloid are age-related and an inherent characteristic of the neurons. Further mechanistic investigations are possible. New therapeutic approaches are suggested that combine inhibition of calcium overloads (calcium channel blockers), reduced ROS damage (melatonin, N-acetyl-cysteine), and bolstered mitochondrial function and energy generation (creatine). Together with newly demonstrated capabilities for adult and aged neuron regeneration and multiplication, i.e. plasticity, these approaches offer new hope toward reversing age-related decrements and damage from neurodegenerative disease.

Divergent enzyme kinetics and structural properties of the two human mitochondrial creatine kinase isoenzymes

The mitochondrial isoenzymes of creatine kinase (MtCK), ubiquitous uMtCK and sarcomeric sMtCK, are key enzymes of oxidative cellular energy metabolism and play an important role in human health and disease. Very little is known about uMtCK in general, or about sMtCK of human origin. Here we have heterologously expressed and purified both human MtCK isoenzymes to perform a biochemical, kinetic and structural characterization. Both isoenzymes occurred as octamers, which can dissociate into dimers. Distinct Stokes' radii of uMtCK and sMtCK in solution were indicative for conformational differences between these equally sized proteins. Both human MtCKs formed 2D-crystals on cardiolipin layers, which revealed further subtle differences in octamer structure and stability. Octameric human sMtCK displayed p4 symmetry with lattice parameters of 145 A, indicating a 'flattening' of the octamer on the phospholipid layer. pH optima and enzyme kinetic constants of the two human isoenzymes were significantly different. A pronounced substrate binding synergism (Kd > Km) was observed for all substrates, but was most pronounced in the forward reaction (PCr production) of uMtCK and led to a significantly lower Km for creatine (1.01 mM) and ATP (0.11 mM) as compared to sMtCK (creatine, 7.31 mM; ATP, 0.68 mM).

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Cloning, Escherichia coli expression, and phase-transition chromatography-based purification of recombinant rabbit heart mitochondrial creatine kinase

A cDNA clone of the mitochondrial sarcomeric creatine kinase cDNA was obtained by screening a rabbit heart library. This cDNA is characterized by a 1257-nucleotide open reading frame encoding a 419-amino-acid protein with a cleavable 39-amino-acid mitochondrial presequence (Accession No. AJ011334). This new member of the guanidino kinase family shows a high degree of sequence similarity with the other phosphagen kinases sequenced so far. The mature enzyme was efficiently expressed in Escherichia coli BL21(DE3) cells as a soluble octameric protein using the pET21 plasmid and purified by a three-step improved method including a final phase-transition chromatography.

Some new aspects of creatine kinase (CK): compartmentation, structure, function and regulation for cellular and mitochondrial bioenergetics and physiology

Creatine kinase (CK) isoenzymes, specifically located at places of energy demand and energy production, are linked by a phosphocreatine/creatine (PCr/Cr) circuit, found in cells with intermittently high energy demands. Cytosolic CKs, in close conjunction with Ca(2+)-pumps, play a crucial role for the energetics of Ca(2+)-homeostasis. Mitochondrial Mi-CK, a cuboidal-shaped octamer with a central channel, binds and crosslinks mitochondrial membranes and forms a functionally coupled microcompartment with porin and adenine nucleotide translocase for vectorial export of PCr into the cytosol. The CK system is regulated by AMP-activated protein kinase via PCr/Cr and ATP/AMP ratios. Mi-CK stabilizes and cross-links cristae- or inner/outer membranes to form parallel membrane stacks and, if overexpressed due to creatine depletion or cellular energy stress, forms those crystalline intramitochondrial inclusions seen in some mitochondrial cytopathy patients. Mi-CK is a prime target for free radical damage by peroxynitrite. Mi-CK octamers, together with CK substrates have a marked stabilizing and protective effect against mitochondrial permeability transition pore opening, thus providing a rationale for creatine supplementation of patients with neuromuscular and neurodegenerative diseases.

The role of creatine kinase in inhibition of mitochondrial permeability transition

Cyclosporin A sensitive swelling of mitochondria isolated from control mouse livers and from the livers of transgenic mice expressing human ubiquitous mitochondrial creatine kinase occurred in the presence of both 40 microM calcium and 5 microM atractyloside which was accompanied by a 2.5-fold increase over state 4 respiration rates. Creatine and cyclocreatine inhibited the latter only in transgenic liver mitochondria. Protein complexes isolated from detergent solubilised rat brain extracts, containing octameric mitochondrial creatine kinase, porin and the adenine nucleotide translocator, were reconstituted into malate loaded lipid vesicles. Dimerisation of creatine kinase in the complexes and exposure of the reconstituted complexes to >200 microM calcium induced a cyclosporin A sensitive malate release. No malate release occurred with complexes containing octameric creatine kinase under the same conditions.