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Effect of experimental colchicine encephalopathy on brain protein synthesis and tubulin metabolism
Abstract:
Colchicine blocks axoplasmic flow and produces neurofibrillary degeneration. Brain slices from mice injected intracerebrally with colchicine incorporated more [14C]leucine into protein and had a decreased uptake of [14C]leucine into the perchloric acid-soluble pool than did their controls. Brain RNA content was decreased and free leucine increased by colchicine-induced encephalopathy. The specific activities of proteins from subcellular fractions of colchicine-injected brain were increased in the nuclear fraction, the 100,000-g supernatant, and its vinblastine-precipitable tubulin. The ratio of the specific activity of the crude mitochondrial fraction to that of the total homogenate was decreased, as would be consistent with impaired movement of newly labeled protein into synaptosomes. Colchicine-injected brain extracts contained one or more cytosol fractions that stimulated ribosomal incorporation of [14C]leucine into protein in a cell-free system. Colchicine-binding-activity measurements indicated loss of soluble and particulate tubulin in colchicine-injected brains; the decrease of soluble tubulin was verified by its selective precipitation with vinblastine. Colchicine encephalopathy did not affect the rate of spontaneous breakdown of in vitro colchicine binding activity. Similarities of colchicine encephalopathy to the neuron's response to axonal damage suggest that colchicine-induced increase in protein synthesis may, in part, reflect a neuronal response to blockage of neuroplasmic transport.
Insights
Colchicine disrupts axoplasmic transport, leading to increased protein synthesis in neurons. This suggests a cellular response to blocked neuroplasmic transport, impacting brain function and potentially causing neurofibrillary degeneration.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Colchicine is known to interfere with microtubule assembly.
- Axoplasmic transport is crucial for neuronal function and integrity.
- Neurofibrillary degeneration is a hallmark of various neurological disorders.
Purpose of the Study:
- To investigate the effects of colchicine on protein synthesis and transport in the brain.
- To elucidate the molecular mechanisms underlying colchicine-induced neurotoxicity.
- To explore the relationship between impaired axoplasmic flow and neuronal protein metabolism.
Main Methods:
- Intracerebral injection of colchicine in mice.
- Measurement of [14C]leucine incorporation into brain proteins.
- Analysis of RNA and free amino acid content in brain tissue.
- Subcellular fractionation and analysis of protein specific activity.
- Assessment of tubulin levels and colchicine-binding activity.
Main Results:
- Colchicine injection increased [14C]leucine incorporation into proteins, particularly in nuclear and supernatant fractions.
- Decreased uptake of [14C]leucine into the soluble pool and reduced brain RNA content were observed.
- Impaired movement of newly synthesized proteins into synaptosomes was indicated by altered specific activity ratios.
- Colchicine treatment led to a loss of both soluble and particulate tubulin.
Conclusions:
- Colchicine-induced encephalopathy alters neuronal protein synthesis and transport.
- The observed increase in protein synthesis may represent a compensatory response to blocked axoplasmic flow.
- Colchicine's effects on tubulin and protein metabolism contribute to neurofibrillary degeneration.