MAP2c prevents arachidonic acid-induced fibril formation of tau: Role of chaperone activity and phosphorylation

Deciphering the alteration of MAP2 interactome caused by a schizophrenia-associated phosphorylation

Microtubule-associated protein 2 (MAP2) is a crucial regulator of dendritic structure and neuronal function, orchestrating diverse protein interactions within the microtubule network. We have shown MAP2 is hyperphosphorylated at serine 1782 (S1782) in schizophrenia and phosphomimetic mutation of S1782 in mice (MAP2S1782E) is sufficient to impair dendritic architecture. We sought to determine how this hyperphosphorylation affects the MAP2 interactome to provide insights into the disorder's mechanisms. We investigated the MAP2 interactome using co-immunoprecipitation and mass spectrometry in MAP2S1782E and MAP2WT mice. We found that S1782E MAP2 led to a substantial disruption of protein-protein interactions relative to WT MAP2. Reduced interactions with PDZ domain-containing proteins, calmodulin-binding proteins, ribosome proteins, and kinesin proteins may all contribute to dendritic impairments induced by S1782E, and may be linked to schizophrenia pathogenesis. Interestingly, novel gain-of-function interactions with PPM1L and KLHL8 nominated these as regulators of phosphoS1782 MAP2 abundance and potential therapeutic targets in schizophrenia.

Involvement of protein L-isoaspartyl methyltransferase in the physiopathology of neurodegenerative diseases: Possible substrates associated with synaptic function

Synaptic dysfunction is a typical pathophysiologic change in neurodegenerative diseases (NDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Hintington's disease (HD) and amyotrophic lateral sclerosis (ALS), which involves protein post-translational modifications (PTMs) including L-isoaspartate (L-isoAsp) formed by isomerization of aspartate or deamidation of asparagine. The formation of L-isoAsp could be repaired by protein L-isoaspartyl methyltransferase (PIMT). Some synaptic proteins have been identified as PIMT potential substrates and play an essential role in ensuring synaptic function. In this review, we discuss the role of certain synaptic proteins as PIMT substrates in neurodegenerative disease, thus providing therapeutic synapse-centered targets for the treatment of NDs.

More than a marker: potential pathogenic functions of MAP2

Microtubule-associated protein 2 (MAP2) is the predominant cytoskeletal regulator within neuronal dendrites, abundant and specific enough to serve as a robust somatodendritic marker. It influences microtubule dynamics and microtubule/actin interactions to control neurite outgrowth and synaptic functions, similarly to the closely related MAP Tau. Though pathology of Tau has been well appreciated in the context of neurodegenerative disorders, the consequences of pathologically dysregulated MAP2 have been little explored, despite alterations in its immunoreactivity, expression, splicing and/or stability being observed in a variety of neurodegenerative and neuropsychiatric disorders including Huntington’s disease, prion disease, schizophrenia, autism, major depression and bipolar disorder. Here we review the understood structure and functions of MAP2, including in neurite outgrowth, synaptic plasticity, and regulation of protein folding/transport. We also describe known and potential mechanisms by which MAP2 can be regulated via post-translational modification. Then, we assess existing evidence of its dysregulation in various brain disorders, including from immunohistochemical and (phospho) proteomic data. We propose pathways by which MAP2 pathology could contribute to endophenotypes which characterize these disorders, giving rise to the concept of a “MAP2opathy”—a series of disorders characterized by alterations in MAP2 function.

ATP Kinetically Modulates Pathogenic Tau Fibrillations

Advanced understanding of Alzheimer's disease (AD) and several tauopathies over the past decades indicates the pathological importance of tau aggregation in these diseases. Herein, we demonstrated that adenosine triphosphate (ATP), a highly charged anionic molecule found abundantly in the cytosol of cells, catalyzes fibrillation of tau as well as human islet amyloid polypeptide, a representative of basic intrinsically disordered proteins. Our results showed that ATP attracts multiple lysine residues of the four-repeat domain of tau (K18) via supramolecular complexation, thereby forming dimers that are converted to nuclei and accelerate fibril elongation. However, ATP was not directly incorporated into the K18 fibrils, suggesting that ATP plays the role of a catalyst, rather than a reactant, during K18 fibrillation. We also characterized the correlation between ATP dyshomeostasis and tau aggregation in the cellular environment. Our multiple biophysical approaches, including native mass spectrometry (MS), small-angle X-ray scattering (SAXS), and molecular dynamics (MD) simulation, provided insights into the molecular-level influence of ATP on the structural changes and fibrillation of tau.

Extracellular Nanomatrix-Induced Self-Organization of Neural Stem Cells into Miniature Substantia Nigra-Like Structures with Therapeutic Effects on Parkinsonian Rats

Substantia nigra (SN) is a complex and critical region of the brain wherein Parkinson's disease (PD) arises from the degeneration of dopaminergic neurons. Miniature SN-like structures (mini-SNLSs) constructed from novel combination of nanomaterials and cell technologies exhibit promise as potentially curative cell therapies for PD. In this work, a rapid self-organization of mini-SNLS, with an organizational structure and neuronal identities similar to those of the SN in vivo, is achieved by differentiating neural stem cells in vitro on biocompatible silica nanozigzags (NZs) sculptured by glancing angle deposition, without traditional chemical growth factors. The differentiated neurons exhibit electrophysiological activity in vitro. Diverse physical cues and signaling pathways that are determined by the nanomatrices and lead to the self-organization of the mini-SNLSs are clarified and elucidated. In vivo, transplantation of the neurons from a mini-SNLS results in an early and progressive amelioration of PD in rats. The sculptured medical device reported here enables the rapid and specific self-organization of region-specific and functional brain-like structures without an undesirable prognosis. This development provides promising and significant insights into the screening of potentially curative drugs and cell therapies for PD.

M1 muscarinic receptor is a key target of neuroprotection, neuroregeneration and memory recovery by i-Extract from Withania somnifera

Memory loss is one of the most tragic symptoms of Alzheimer's disease. Our laboratory has recently demonstrated that 'i-Extract' of Ashwagandha (Withania somnifera) restores memory loss in scopolamine (SC)-induced mice. The prime target of i-Extract is obscure. We hypothesize that i-Extract may primarily target muscarinic subtype acetylcholine receptors that regulate memory processes. The present study elucidates key target(s) of i-Extract via cellular, biochemical, and molecular techniques in a relevant amnesia mouse model and primary hippocampal neuronal cultures. Wild type Swiss albino mice were fed i-Extract, and hippocampal cells from naïve mice were treated with i-Extract, followed by muscarinic antagonist (dicyclomine) and agonist (pilocarpine) treatments. We measured dendritic formation and growth by immunocytochemistry, kallikrein 8 (KLK8) mRNA by reverse transcription polymerase chain reaction (RT-PCR), and levels of KLK8 and microtubule-associated protein 2, c isoform (MAP2c) proteins by western blotting. We performed muscarinic receptor radioligand binding. i-Extract stimulated an increase in dendrite growth markers, KLK8 and MAP2. Scopolamine-mediated reduction was significantly reversed by i-Extract in mouse cerebral cortex and hippocampus. Our study identified muscarinic receptor as a key target of i-Extract, providing mechanistic evidence for its clinical application in neurodegenerative cognitive disorders.