The Type 2 Diabetes Factor Methylglyoxal Mediates Axon Initial Segment Shortening and Alters Neuronal Function at the Cellular and Network Levels

Abstract

Recent evidence suggests that alteration of axon initial segment (AIS) geometry (i.e., length or location along the axon) contributes to CNS dysfunction in neurological diseases. For example, AIS length is shorter in the prefrontal cortex of type 2 diabetic mice with cognitive impairment.To determine the key type 2 diabetes-related factor that produces AIS shortening we modified levels of insulin, glucose, or the reactive glucose metabolite methylglyoxal in cultures of dissociated cortices from male and female mice and quantified AIS geometry using immunofluorescent imaging of the AIS proteins AnkyrinG and βIV spectrin. Neither insulin nor glucose modification altered AIS length.Exposure to 100 but not 1 or 10 µM methylglyoxal for 24 h resulted in accumulation of the methylglyoxal-derived advanced glycation end-product hydroimidazolone and produced reversible AIS shortening without cell death. Methylglyoxal-evoked AIS shortening occurred in both excitatory and putative inhibitory neuron populations and in the presence of TTX. In single-cell recordings resting membrane potential was depolarized at 0.5-3 h and returned to normal at 24 h. In multi-electrode array recordings methylglyoxal produced an immediate ~300% increase in spiking and bursting rates that returned to normal within 2 min, followed by a ~20% reduction of network activity at 0.5-3 h and restoration of activity to baseline levels at 24 h. AIS length was unchanged at 0.5-3 h despite the presence of depolarization and network activity reduction. Nevertheless, these results suggest that methylglyoxal could be a key mediator of AIS shortening and disruptor of neuronal function during type 2 diabetes. Significance StatementSmall changes in the structure of the axon initial segment affect neuronal function and may be a key mediator of neurological complications in various disease states. However, the specific disease factors that mediate structural changes at the axon initial segment are relatively unknown. This is the first study to show that increase of methylglyoxal is sufficient to reduce axon initial segment length and modulate neuronal function at the cellular and network levels. Methylglyoxal is a disease factor implicated in a wide variety of conditions including type 2 diabetes, Alzheimer's disease, and aging. Thus, these findings could significantly impact the understanding of neurological complications in several disease states and are of broad pathophysiological relevance.

O-GlcNAcylation is crucial for sympathetic neuron development, maintenance, functionality and contributes to peripheral neuropathy

“…T2D is a complication that involves hyperglycemia and hyperinsulinemia ( Thomas et al, 2019 ). Previous studies have established in vitro T2D models using heart organoids and primary neurons by culturing the cells in high glucose combined with high insulin [1.14 nM ( Lewis-Israeli et al, 2021 ) to 700 nM ( Griggs et al, 2021 )] conditions. The B27 supplement contains about 60 nM insulin, which is higher than the average level in the body [about 170 pM ( Lewis-Israeli et al, 2021 )].…”

On the effects of diabetes mellitus on the mechanical properties of DRG sensory neurons and their possible relation with diabetic neuropathy

“…However, in hyperglycemic conditions, in which sorbitol accumulates, gene response is not activated, and osmotic disorder continues [10]. Also, the production of methylglyoxal, a highly reactive compound resulting from glycolysis and related to the development of type 2 diabetes, affects the cellular function of neurons by shortening and changing the geometry of the axon initial segment [11]. In addition, excess reactive oxygen species (ROS) production causes oxidation of membrane lipids, affecting its integrity [12].…”

“…It can be hypothesized from this that DM-induced alterations of molecule interactions in the plasma membrane modify its mechanical properties, lead to mechanotransducer-molecule malfunction, and/or impair action-potential generation and propagation. Although it cannot be ruled out that the actin and myosin network that forms part of the cytoskeleton that underlies the plasma membrane, which participates in the control of the cell shape and allows them to resist mechanical stress and exert forces on neighboring cells [11], could also be altered. The present work is aimed at tackling this question by investigating whether the mechanical properties of DRG sensory-neuron membranes are altered by the induction of DN in a murine model, as well as the possible correlation between membrane modifications and neuron responsiveness to stimuli.…”