Brain, Vol. 122, No. 11, 2109-2118,
November 1999
© 1999 Oxford University Press
Invited review |
Neurofilament and tubulin gene expression in progressive experimental diabetes
Failure of synthesis and export by sensory neurons
1 Department of Clinical Neurosciences and Neuroscience Research Group and 2 Departments of Pathology and Clinical Neurosciences, and Neuroscience Research Group, The University of Calgary
Correspondence to:
Dr D. W. Zochodne, University of Calgary, 182a Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1 E-mail: dzochodn{at}ucalgary.ca
In human and experimental diabetes, the relationship between molecular abnormalities in perikarya of sensory neurons and structural abnormalities in their distal axons is largely unexplored. In this study we examined neurofilament (Nf) and tubulin messenger RNA (mRNA) expression and their incorporation into distal sensory axons during progressive streptozotocin-induced diabetes in rats. After 2 and 6 months of diabetes, we measured mRNA levels of all three Nf subunits, B50 [growth associated protein-43 (GAP-43)] and 
-tubulin in L4–L6 dorsal root ganglia using Northern analysis. The same animals underwent morphometric studies of myelinated fibres by light microscopy and quantitative analysis of Nf and microtubule numbers and density within sural myelinated and unmyelinated axons. Multifibre in vivo sensory and motor conduction nerve recordings confirmed slowing of conduction velocities in diabetic rats indicating experimental neuropathy. mRNA levels for the three Nf subunits, B50 (GAP-43) and -tubulin were unchanged from controls at 2 months, but were decreased by 26–46% at 6 months. These changes accompanied declines in Nf numbers and densities within large myelinated sensory axons, and Nf numbers in unmyelinated fibres by 6 months. Microtubule numbers and densities were similarly reduced in large myelinated axons, and microtubule numbers reduced in small myelinated and unmyelinated axons in diabetes at 6, but not 2 months. Axonal atrophy was observed in unmyelinated fibres at 6 months. Our findings indicate that decreased mRNA expression of cytoskeletal proteins in sensory neurons accompanies a reduction in their incorporation into distal axons. These changes imply that there is a direct link between pathological changes in the sensory neuron and alterations of its distal branches from experimental diabetes. The changes in gene expression in diabetes are unique and differ from those that develop after axotomy.
diabetic neuropathy; dorsal root ganglia; conduction velocity; streptozotocin
GAP-43 = growth associated protein-43 (B50); mRNA = messenger RNA; Nf = neurofilament; Nf-H = Nf-heavy subunit; Nf-L = Nf-light subunit; Nf-M = Nf-medium subunit; STZ = streptozotocin
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