Tau haploinsufficiency causes prenatal loss of dopaminergic neurons in the ventral tegmental area and reduction of transcription factor orthodenticle homeobox 2 expression

The six brain-specific TAU isoforms and their role in Alzheimer's disease and related neurodegenerative dementia syndromes

INTRODUCTION

Alternative splicing of the human MAPT gene generates six brain-specific TAU isoforms. Imbalances in the TAU isoform ratio can lead to neurodegenerative diseases, underscoring the need for precise control over TAU isoform balance. Tauopathies, characterized by intracellular aggregates of hyperphosphorylated TAU, exhibit extensive neurodegeneration and can be classified by the TAU isoforms present in pathological accumulations.

METHODS

A comprehensive review of TAU and related dementia syndromes literature was conducted using PubMed, Google Scholar, and preprint server.

RESULTS

While TAU is recognized as key driver of neurodegeneration in specific tauopathies, the contribution of the isoforms to neuronal function and disease development remains largely elusive.

DISCUSSION

In this review we describe the role of TAU isoforms in health and disease, and stress the importance of comprehending and studying TAU isoforms in both, physiological and pathological context, in order to develop targeted therapeutic interventions for TAU-associated diseases.

HIGHLIGHTS

MAPT splicing is tightly regulated during neuronal maturation and throughout life. TAU isoform expression is development-, cell-type and brain region specific. The contribution of TAU to neurodegeneration might be isoform-specific. Ineffective TAU-based therapies highlight the need for specific targeting strategies.

Roles of Transcription Factors in the Development and Reprogramming of the Dopaminergic Neurons

The meso-diencephalic dopaminergic (mdDA) neurons regulate various critical processes in the mammalian nervous system, including voluntary movement and a wide range of behaviors such as mood, reward, addiction, and stress. mdDA neuronal loss is linked with one of the most prominent human movement neurological disorders, Parkinson’s disease (PD). How these cells die and regenerate are two of the most hotly debated PD research topics. As for the latter, it has been long known that a series of transcription factors (TFs) involves the development of mdDA neurons, specifying cell types and controlling developmental patterns. In vitro and in vivo, TFs regulate the expression of tyrosine hydroxylase, a dopamine transporter, vesicular monoamine transporter 2, and L-aromatic amino acid decarboxylase, all of which are critical for dopamine synthesis and transport in dopaminergic neurons (DA neurons). In this review, we encapsulate the molecular mechanism of TFs underlying embryonic growth and maturation of mdDA neurons and update achievements on dopaminergic cell therapy dependent on knowledge of TFs in mdDA neuronal development. We believe that a deeper understanding of the extrinsic and intrinsic factors that influence DA neurons’ fate and development in the midbrain could lead to a better strategy for PD cell therapy.

Much More Than a Cytoskeletal Protein: Physiological and Pathological Functions of the Non-microtubule Binding Region of Tau

Tau protein (MAPT) is classified as a microtubule-associated protein (MAP) and is believed to regulate the axonal microtubule arrangement. It belongs to the tau/MAP2/MAP4 family of MAPs that have a similar microtubule binding region at their carboxy-terminal half. In tauopathies, such as Alzheimer's disease, tau is distributed more in the somatodendritic compartment, where it aggregates into filamentous structures, the formation of which correlates with cognitive impairments in patients. While microtubules are the dominant interaction partners of tau under physiological conditions, tau has many additional interaction partners that can contribute to its physiological and pathological role. In particular, the amino-terminal non-microtubule binding domain (N-terminal projection region, NTR) of tau interacts with many partners that are involved in membrane organization. The NTR contains intrinsically disordered regions (IDRs) that show a strong evolutionary increase in the disorder and may have been the basis for the development of new, tau-specific interactions. In this review we discuss the functional organization of the tau protein and the special features of the tau non-microtubule binding region also in the connection with the results of Tau KO models. We consider possible physiological and pathological functions of tau's non-microtubule interactions, which could indicate that interactions mediated by tau's NTR and regulated by far-reaching functional interactions of the PRR and the extreme C-terminus of tau contribute to the pathological processes.

Tau knockout exacerbates degeneration of parvalbumin-positive neurons in substantia nigra pars reticulata in Parkinson's disease-related α-synuclein A53T mice

α-Synuclein (α-syn)-induced neurotoxicity has been generally accepted as a key step in the pathogenesis of Parkinson's disease (PD). Microtubule-associated protein tau, which is considered second only to α-syn, has been repeatedly linked with PD in association studies. However, the underlying interaction between these two PD-related proteins in vivo remains unclear. To investigate how the expression of tau affects α-syn-induced neurodegeneration in vivo, we generated triple transgenic mice that overexpressed α-syn A53T mutation in the midbrain dopaminergic neurons (mDANs) with different expression levels of tau. Here, we found that tau had no significant effect on the A53T α-syn-mediated mDANs degeneration. However, tau knockout could modestly promote the formation of α-syn aggregates, accelerate the severe and progressive degeneration of parvalbumin-positive (PV⁺) neurons in substantia nigra pars reticulata (SNR), accompanied with anxiety-like behavior in aged PD-related α-syn A53T mice. The mechanisms may be associated with A53T α-syn-mediated specifically successive impairment of N-methyl-d-aspartate receptor subunit 2B (NR2B), postsynaptic density-95 (PSD-95) and microtubule-associated protein 1A (MAP1A) in PV⁺ neurons. Our study indicates that MAP1A may play a beneficial role in preserving the survival of PV⁺ neurons, and that inhibition of the impairment of NR2B/PSD-95/MAP1A pathway, may be a novel and preferential option to ameliorate α-syn-induced neurodegeneration.

The loss of dopaminergic neurons in DEC1 deficient mice potentially involves the decrease of PI3K/Akt/GSK3β signaling

Here we study the effects of differentiated embryonic chondrocyte gene 1(DEC1) deficiency on midbrain dopaminergic(DA) neurons in the substantia nigra pars compacta(SNpc) through behavioral, histological and molecular analysis. We have found that compared to the age-matched WT mice, DEC1 deficient mice show a decrease in locomotor activity and motor coordination, which shows the main features of Parkinson's disease(PD). But there is no significant difference in spatial learning and memory skills between WT and DEC1 KO mice. Compared to the age-matched WT mice, DEC1 deficient mice exhibit the loss of DA neurons in the SNpc and reduction of dopamine and its metabolites in the striatum. The activated caspase-3 and TH/TUNEL⁺ cells increase in the SNpc of 6- and 12-month-old DEC1 KO mice compared to those of the age-matched WT mice. But we haven't found any NeuN/TUNEL⁺ cell increase in the hippocampus of the above two types of mice at the age of 6 months. Furthermore, DEC1 deficiency leads to a significant inhibition of PI3K/Akt/GSK3β signaling pathway. Additionally, LiCl could rescue the DA neuron loss of midbrain in the 6-month-old DEC1 KO mice. Taken together, the loss of DA neurons in the DEC1 deficient mice potentially involves the downregulation of PI3K/Akt/GSK3β signaling.

Hydrophobic tagging-mediated degradation of Alzheimer's disease related Tau

HyT-Tau-CPP reduced Tau levels in Alzheimer's disease (AD) mouse model, and appeared to be a promising candidate for AD treatment.