Delayed detyrosination of alpha-tubulin from parallel fibre axons and its correlation with impaired synaptogenesis in hypothyroid rat cerebellum

Tubulin post-translational modifications control neuronal development and functions

Microtubules (MTs) are an essential component of the neuronal cytoskeleton; they are involved in various aspects of neuron development, maintenance, and functions including polarization, synaptic plasticity, and transport. Neuronal MTs are highly heterogeneous due to the presence of multiple tubulin isotypes and extensive post‐translational modifications (PTMs). These PTMs—most notably detyrosination, acetylation, and polyglutamylation—have emerged as important regulators of the neuronal microtubule cytoskeleton. With this review, we summarize what is currently known about the impact of tubulin PTMs on microtubule dynamics, neuronal differentiation, plasticity, and transport as well as on brain function in normal and pathological conditions, in particular during neuro‐degeneration. The main therapeutic approaches to neuro‐diseases based on the modulation of tubulin PTMs are also summarized. Overall, the review indicates how tubulin PTMs can generate a large number of functionally specialized microtubule sub‐networks, each of which is crucial to specific neuronal features.

Congenital hypothyroidism is associated with intermediate filament misregulation, glutamate transporters down-regulation and MAPK activation in developing rat brain

Developmental thyroid hormone (TH) deficiency leads to mental retardation and neurological deficits in humans. In this study, congenital hypothyroidism was induced in rats by adding 0.05% 6-propyl-2-thiouracil in the drinking water during gestation and suckling period. This treatment induced hyperphosphorylation of neurofilaments, the neuronal intermediate filament (IF) proteins, of heavy, medium and low molecular weight (NF-H, NF-M and NF-L, respectively) without altering the phosphorylation level of astrocyte IF proteins, glial fibrillary acidic protein (GFAP) and vimentin in cerebral cortex of rats. NF-H was hyperphosphorylated on KSP repeats in the carboxy-terminal tail domain. Furthermore, the immunocontent of GFAP and NF subunits was down-regulated, while vimentin was unaltered both in tissue homogenate and in cytoskeletal fraction of hypothyroid animals. Moreover, we verified the immunocontent of astrocyte glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) as well as activation of mitogen-activated protein kinases (MAPKs) in hypothyroid rats. Results showed that hypothyroidism is associated with decreased GLAST and GLT-1 immunocontent. Additionally, we demonstrated increased extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation without altering Jun N-terminal kinase (JNK) and p38(MAPK) phosphorylation. However, total JNK levels were down-regulated. Taken together, these results suggest that the thyroid status could modulate the integrity of neuronal cytoskeleton acting on the endogenous NF-associated phosphorylating system and that such effect could be related to glutamate-induced excitotoxicity, as well as ERK1/2 and JNK modulation. These events could be somehow related to the neurological dysfunction described in hypothyroidism.