Experimental diabetic neuropathy: impairment of slow transport with changes in axon cross-sectional area.

Abstract

Analysis of slow axonal transport in the sciatic and primary visual systems of rats with streptozotocininduced diabetes of 4-6 weeks duration showed impairment of the transport of neurofilament subunits, tubulin, actin, and a 30-and a 60-kDa polypeptide in both systems. The degree of impairment was not uniform. Transport of polypeptide constituents of the slow component b, such as the 30-and 60-kDa polypeptides, appeared to be more severely affected than the transport of constituents of the slow component a, such as neurorflaments. Morphometric analysis of sciatic axons revealed a proximal increase and a distal decrease of axonal cross-sectional area. It is proposed that impairment of axoplasmic transport and changes of axonal size are related. Transport impairment results in a larger number of neurofilaments, microtubules, and other polypeptides in the proximal region of the axon, which increases in size, whereas fewer neurofilaments, microtubules, and other polypeptides reach the distal axons that show a size decrease. Such changes in axonal transport and area are likely to occur in other diabetic animal models and in human diabetes.Peripheral nerve dysfunction is a common complication of human diabetes mellitus (1,2 (26, 27). Animals were sacrificed 25 days after labeling by intra-aortic perfusion of saline, and the primary visual and sciatic systems were dissected out. Optic nerves and tracts were cut into 3-mm segments; the chiasma, which measured approximately 2 mm, and the superior colliculus were also obtained. The sciatic system from the spinal motor roots to the tibial nerve was cut in 3-mm segments. Individual nerve segments were processed for electrophoresis and fluorography as previously described (27,28). Before electrophoresis, the total radioactivity of each segment was determined. The distribution of the radioactivity related to selected polypeptides of the slow transport was assessed either by determining the radioactivity in the appropriate gel bands or by scanning the fluorogram (28)(29)(30)

Morphometry of Dorsal Root Ganglion in Chronic Experimental Diabetic Neuropathy

“…Scott et al (33) examined neurofilament and tubulin mRNA expression and demonstrated that a time-dependent decrease in mRNA expression of cytoskeletal proteins in sensory neurons accompanies a reduction in their incorporation into distal axons. These abnormalities build on the observation by Medori et al (34), who demonstrated axonal dwindling secondary to alterations in the axonal transport of structural proteins, with enlargement proximally and atrophy distally.…”

Axon Transport and Neuropathy

“…Indeed, for >30 years axon transport abnormalities were recognized to have a role in PN caused by DM. 19 DM may lead to alterations in cytoskeletal components, such as actin, neurofilament, and tubulin that are essential for normal intracellular (axon) transport, either by direct glycation in the context of hyperglycemia or as a consequence of impaired gene expression. 20e23 For example, tubulin glycosylation in DM impairs polymerization and alters microtubule dynamics which is essential for trafficking intracellular macromolecules and organelles 24 along microtubule networks.…”

Intermediate Filaments in Neurodegenerative Diseases

“…In agreement with this, multiple abnormalities of NF biology were identified in models of diabetes. An impairment of the axonal transport of NFs, actin and tubulin concomitant with a proximal increase and a distal decrease of axonal calibers were observed in rats with streptozotocin-induced diabetes and in BioBreeding rats (a model of spontaneous type I diabetes) [131,132]. The distal axonal atrophy is accompanied by a concomitant NF loss in this region [133], and accumulations of highly phosphorylated NF epitopes are present in proximal axonal segments of dorsal root ganglia sensory neurons from diabetic patients [134].…”