Ca2-activated proteinases, protein degradation and muscular dystrophy

The role of magnetosomes in cellular homeostasis disorder and development of pathology

Literature data on magnitosomes, the nanocrystals formed during natural biomineralization have been summarized. Special attention is paid to magnitosome effect on physiological and biochemical processes, impairments of cell homeostasis and development of various pathologies. It is suggested that the increase in quantity and sizes of magnetosomes, spatial rearrangement, and modification of their crystalline substance exert substantial effect on development of pathological processes.

Active oxygen in neuromuscular disorders

Although muscle and nerve are reasonably well protected against active oxygen and related free radicals, environmental or inherited malfunctions can overpower their defences. Active oxygen is involved in many neuropathies and myopathies. In every case the damage is caused by agents which exert effects disproportionately greater than the quantities encountered, through a variety of amplification mechanisms. We can categorize these amplification mechanisms as follows: (a) non-replacement of targets (e.g. loss of genetic information, ataxia telangectasia being an hereditary ataxia in which an oxygen mediated chromosomal instability is apparent), (b) non-removal of unwanted materials (e.g. lipofuscin accumulation in brain and heart), (c) redox cycling, usually involving catalysis by trace-metal ions (e.g. some forms of Parkinsonism), (d) non-redox catalysis (e.g. toxicity in cardiac muscle or brain due to vanadium or aluminium respectively), (e) modification of ion transport (e.g. calcium ionophore or acrylamide induce histopathological changes in muscle, similar in some respects to those seen in Duchenne muscular dystrophy), (f) compromised defences (e.g. muscle and nerve become particularly susceptible to free radical damage after loss of the protective actions of vitamin E), and (g) amplification by inflammatory and immune responses (e.g. multiple sclerosis, reperfusion injury to brain and heart, and traumatic injury to nervous tissue). Unfortunately, a variety of therapeutic agents which might be expected to protect against almost every conceivable form of oxygen mediated damage have proved clinically ineffective in most of these disorders. The reasons for this will be explored with an emphasis on common features, differences, mechanisms, and potential therapeutic approaches.

Hypogravity-induced atrophy of rat soleus and extensor digitorum longus muscles

Prolonged exposure of humans to hypogravity causes weakening of their skeletal muscles. This problem was studied in rats exposed to hypogravity for 7 days aboard Spacelab 3. Hindlimb muscles were harvested 12-16 hours postflight for histochemical, biochemical, and ultrastructural analyses. The majority of the soleus and extensor digitorum longus fibers exhibited simple cell shrinkage. However, approximately 1% of the fibers in flight soleus muscles appeared necrotic. Flight muscle fibers showed increased glycogen, lower subsarcolemmal staining for mitochondrial enzymes, and fewer subsarcolemmal mitochondria. During atrophy, myofibrils were eroded by multiple focal losses of myofilaments; lysosomal autophagy was not evident. Tripeptidylaminopeptidase and calcium-activated protease activities of flight soleus fibers were significantly increased, implying a role in myofibril breakdown. Simple fiber atrophy appears to account for muscle weakening during spaceflight, but fiber necrosis is also a contributing factor.

Gene structure of calcium-dependent protease retains the ancestral organization of the calcium-binding protein gene

The gene structure of calcium-dependent protease (Ca2+-protease) was determined. It comprises at least 21 exons, and these were assigned to the 4 functional domains of the protease. The protease domain does not show clear correlation between exons and functional units, but the calmodulin-like calcium-binding domain shows strong correlation. Each of the 4 consecutive calcium-binding regions in the C-terminal part of Ca2+-protease is encoded by one exon. This gene structure supports the idea that the 4 calcium-binding regions of calcium-binding proteins such as calmodulin arose by 2 steps of gene duplication.