Reduced axonal transport of 10S acetylcholinesterase in dystrophic mice

On the specificity of the acetylcholinesterase defect in dystrophic mice

The tetrameric form of acetylcholinesterase (AChE) in ReJ/129 dystrophic mice was demonstrated to be absent from endplate-poor regions of skeletal muscle but present in endplate-rich regions. Skeletal muscle secreted normal amounts of this form of AChE. Visceral organs had normal amounts and distribution of the AChE molecular forms. These results suggest that the AChE defect in dystrophic mice is limited to skeletal muscle, and the defect does not reflect an abnormality of AChE synthesis but probably reflects an inability to incorporate the enzyme into skeletal muscle membranes.

Axonal transport in mdx mouse sciatic nerve

Anterograde and retrograde flows of acetylcholinesterase (AChE) in sciatic nerves of adult mdx mice were compared with those of normal mice. Specific molecular forms of AChE were resolved by high-performance liquid chromatography such that slow anterograde (G1 + G2), fast anterograde and fast retrograde (G4 and A12) flows could be simultaneously studied. Although we found no difference in the total AChE activity and the molecular forms in non-ligated nerves between mdx and the normal mice, ligated nerves showed significant differences. The total AChE activity accumulated at the proximal segment of ligated nerve was higher in mdx mice than in normal mice after 24 h ligation. The G1 + G2 molecular forms were accumulated more in the proximal segment of mdx than the normal. A12, on the other hand, was more abundant in both segments of mdx mice than the normal. No statistically significant difference in the accumulated amount of G4 molecular form was present between mdx and the normal mice at either proximal or distal segment. These results indicated that axonal flow in sciatic nerve likely plays a role in muscle regeneration, and that the transport machinery in dystrophin-deficient mdx neuron is probably normal.

Reduced axonal transport of the G4 molecular form of acetylcholinesterase in the rat sciatic nerve during aging

Aging in the sciatic nerve of the rat is characterized by various alterations, mainly cytoskeletal impairment, the presence of residual bodies and glycogen deposits, and axonal dystrophies. These alterations could form a mechanical blockade in the axoplasm and disturb the axoplasmic transports. However, morphometric studies on the fiber distribution indicate that the increase of the axoplasmic compartment during aging could obviate this mechanical blockade. Analysis of the axoplasmic transport, using acetylcholinesterase (AChE) molecular forms as markers, demonstrates a reduction in the total AChE flow rate, which is entirely accounted for by a significant bidirectional 40-60% decrease in the rapid axonal transport of the G4 molecular form. However, the slow axoplasmic flow of G1 + G2 forms, as well as the rapid transport of the A12 form of AChE, remain unchanged. Our results support the hypothesis that the alterations observed in aged nerves might be related either to the impairment in the rapid transport of specific factor(s) or to modified exchanges between rapidly transported and stationary material along the nerves, rather than to a general defect in the axonal transport mechanisms themselves.

Skeletal muscle acetylcholinesterase molecular forms in amyotrophic lateral sclerosis

Acetylcholinesterase (AChE) molecular forms in muscle biopsies from control and amyotrophic lateral sclerosis (ALS) patients were extracted under low (G: globular forms) and high (A: asymmetric forms) ionic strength conditions and were evaluated by velocity sedimentation analysis. Total AChE activity in endplate-containing ALS muscle sections was reduced by an average of 65% of control muscle levels. This decrement resulted from an almost complete disappearance of 9.5S (G4) and 8.0S (A4) AChE and significant decreases in the 3.8S (G1), 12.1S (A8), and 15.8S (A12) forms (66%, 9%, and 25% of control, respectively). In most of the ALS biopsies examined, ultrastructural-cytochemical analysis revealed large reductions in AChE reaction product of both synaptic infoldings (extracellular) and sarcoplasmic reticulum (intracellular) of the muscles' motor endplate regions. These data are compatible with the view that alterations observed in AChE forms from ALS muscles are related to disturbances in the normal "trophic" interactions between nerve and muscle.

Decreased G4 (10S) acetylcholinesterase content in motor nerves to fast muscles of dystrophic 129/ReJ mice: lack of a specific compartment of nerve acetylcholinesterase?

Acetylcholinesterase (AChE; EC 3.1.1.7) activity and the distribution of its molecular forms were studied in the nervous system of normal and dystrophic 129/ReJ mice, including the sciatic-tibial nerve trunk and motor nerves to slow- and fast-twitch muscles. In normal mice, motor nerves to the slow-twitch soleus exhibited a low AChE activity together with a low level of G4 (10S form) as compared with nerves of the predominantly fast-twitch plantaris and extensor digitorum longus. In contrast, in dystrophic mice, the AChE activity as well as the G4 content of nerves to the fast-twitch muscles were low, displaying an AChE content similar to that of the nerve of the soleus muscle. In the sciatic-tibial nerve trunk, the AChE activity decreased along the nerve in an exponential mode, at rates that were similar in both conditions. However, in dystrophic mice, the AChE activity was reduced throughout the nerve length by a constant value of approximately 180 nmol/h/mg protein. Further analyses indicated that AChE in this nerve trunk was distributed among two compartments, a decaying and a constant one. The decay involved exclusively the globular forms. The activity of A12 (16S form) remained constant along the nerve and was similar in both normal and dystrophic mice. In addition, according to the equation describing the decay of AChE, the reduction in enzymatic activity observed in the dystrophic mice affected mainly G4 in the constant compartment. Brain, spinal cord, sympathetic ganglia, and serum, which were also examined, showed no remarkable differences between the two conditions in their G4 content. The AChE abnormalities that we found in nervous tissues of 129/ReJ dystrophic mice were confined to the motor system.

The acetylcholinesterase abnormality in dystrophic mice is a reflection of a maturational defect

Juvenile mice of the ReJ/129 strain exhibit a distribution of acetylcholinesterase molecular forms that is similar to the pattern previously observed in dystrophic mice. The change to an adult distribution of the enzyme occurs at about 3 weeks of age which is also when dystrophic signs first become evident. It is suggested that dystrophic mouse muscle fails to mature with respect to the molecular forms of acetylcholinesterase.

Axonal transport of acetylcholinesterase in the diabetic mutant mouse

During the development of diabetic neuropathy in the mouse C57BL/Ks (db/db), the axonal transport of AChE molecular forms was tested in the sciatic nerve, by measuring the accumulation of enzyme activity in front of a nerve transection. No alteration of the fast flow rate of G4 and A12 molecular forms was found until 220 days of age. On the other hand, a reduced flow rate of G1 and G2 molecular forms, probably conveyed by slow axoplasmic flow, was noticed in the late phase of diabetic neuropathy. This result is consistent with the view that axonal dwindling could be related to disturbances of slow axonal transport and that the reduction in conduction velocity, observed at an earlier stage, may be due to other causes.

Asymmetric and globular forms of AChE in slow and fast muscles of 129/ReJ normal and dystrophic mice

Acetylcholinesterase activities and molecular forms were studied in normal and dystrophic 129/ReJ mice, focusing on four predominantly fast-twitch muscles and the slow-twitch soleus. The asymmetric and globular forms were analyzed separately so that the effect of dystrophy on each form could be determined. This comparative study showed the following. (1) In the normal condition, each muscle exhibited a distinct distribution of the molecular forms. (2) The diversity among the fast muscles resulted mainly from variations in the proportions of the three globular forms; in contrast, these muscles showed a constant and precise A12/A8/A4 ratio. (3) The slow-twitch soleus clearly differed from the other muscles in its low acetylcholinesterase activity and distinct distribution of the molecular forms, characterized by a low level of G4 and a peculiar ratio among its asymmetric forms, resulting from a relative increase of the A8 and A4 forms. (4) In dystrophic mice, the diversity of the acetylcholinesterase distribution was lost; all the fast muscles displayed profiles exhibiting the characteristics typical of the soleus. The fast-twitch extensor digitorum longus, sternomastoid, and plantaris converged towards an identical set of acetylcholinesterase molecules. (5) In contrast, the acetylcholinesterase activity and molecular forms of the soleus were only slightly affected by the disease. These results reveal that the dystrophy modifies both categories of molecular forms of acetylcholinesterase in a very precise manner. Such complex changes, which are highly reproducible in a variety of different muscles, are unlikely to result from nonspecific reactions secondary to the disease.

Thermal inactivation of the molecular forms of acetylcholinesterase and butyrylcholinesterase

To compare acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) and butyrylcholinesterase (acylcholine acylhydrolase, EC 3.1.1.8), we utilized the physical parameter of thermolability. In serum or muscle extracts from mouse and rat, butyrylcholinesterase was inactivated as a unimodal function of temperature. Inactivation began at 51 degrees C and was complete at 54-57 degrees C (depending upon time of incubation). Acetylcholinesterase was inactivated in two stages. A 60% decrease in activity from 42 to 48 degrees C was followed by a plateau. The second stage of inactivation began at 51 degrees C and was complete at 57-60 degrees C (depending upon time of incubation). Sucrose density gradients revealed that the partial loss of acetylcholinesterase activity at 48 degrees C was due to inactivation of the monomeric 4 S enzyme, which was the most thermolabile molecular form in each tissue examined. When heated after isolation on density gradients, most of the forms of acetylcholinesterase and butyrylcholinesterase lost activity as a single exponential function of time. The monomers of both enzymes were inactivated fastest. Inactivation of the larger froms was slower and required higher temperatures. Tetrameric 10 S acetylcholinesterase was unique in following a time course that could only be fitted by a double exponential equation (i.e., when this form was heated to 55 degrees C, almost 60% of the activity showed a short half-life while the remainder showed a long half-life). This behavior did not reflect differences in the thermolability of soluble and membrane-derived tetramers.

Axonal transport dysfunction in dystrophia myotonica

Axonal transport of acetylcholinesterase (AChE) was measured in the median and sural nerves of a subject who suffered from dystrophia myotonica and in a control subject. It was found that the basal activity of AChE was increased in myotonic nerves while its proximodistal transport was inhibited.