Role of Class III phosphoinositide 3-kinase in the brain development: possible involvement in specific learning disorders

Targeting VPS34 in autophagy: An update on pharmacological small-molecule compounds

VPS34 is well-known to be the unique member of the class III phosphoinositide 3-kinase (PI3K) family, forming VPS34 complex 1 and complex 2, which are involved in several key physiological processes. Of note, VPS34 complex 1 is an important node of autophagosome generation, which controls T cell metabolism and maintains cellular homeostasis through the autophagic pathway. And, VPS34 complex 2 is involved in endocytosis as well as vesicular transport, and is closely related to neurotransmission, antigen presentation and brain development. Due to the two important biological functions of VPS34, its dysregulation can lead to the development of cardiovascular disease, cancer, neurological disorders, and many types of human diseases by altering normal human physiology. Thus, in this review, we not only summarize the molecular structure and function of VPS34, but demonstrate the relationships between VPS34 and human diseases. Moreover, we further discuss the current small molecule inhibitors targeting VPS34 based upon the structure and function of VPS34, which may provide an insight into the future targeted drug development.

Beclin1-mediated interplay between autophagy and apoptosis: New understanding

The definition for autophagy holds a 'single' meaning as a conserved cellular process that constitutes a recycling pathway for damaged organelles and long-lived proteins to maintain nutrient homeostasis and mediate quality control within the cell. But this process of autophagy may behave ambiguously depending on the physiological stress as the stress progresses in the cellular microenvironment; the 'single' meaning of the autophagy changes from the 'cytoplasmic turnover process' to 'tumor suppressive' and a farther extent, 'tumor promoter' process. In a tumorigenic state, the chemotherapy-mediated resistance and intolerance due to upregulated autophagy in cancer cells have become a significant concern. This concern has provided insight to the scientific community to enter into the arena of cross-talk between autophagy and apoptosis. Recent findings and ongoing research have provided insights on some of the key regulators of this cross-talk; one of them is Beclin1 and their involvement in the physiological and the pathophysiological processes; however, reconciliation of these two forms of death remains an arena to be explored extensively. This review sheds light on the interplay between autophagy and apoptosis, emphasizing one of the key players, Beclin1, and its importance in health and diseases.

Genetic Variation in PADI6-PADI4 on 1p36.13 Is Associated with Common Forms of Human Generalized Epilepsy

We performed a genome-wide association study (GWAS) to identify genetic variation associated with common forms of idiopathic generalized epilepsy (GE) and focal epilepsy (FE). Using a cohort of 2220 patients and 14,448 controls, we searched for single nucleotide polymorphisms (SNPs) associated with GE, FE and both forms combined. We did not find any SNPs that reached genome-wide statistical significance (p ≤ 5 × 10⁻⁸) when comparing all cases to all controls, and few SNPs of interest comparing FE cases to controls. However, we document multiple linked SNPs in the PADI6-PADI4 genes that reach genome-wide significance and are associated with disease when comparing GE cases alone to controls. PADI genes encode enzymes that deiminate arginine to citrulline in molecular pathways related to epigenetic regulation of histones and autoantibody formation. Although epilepsy genetics and treatment are focused strongly on ion channel and neurotransmitter mechanisms, these results suggest that epigenetic control of gene expression and the formation of autoantibodies may also play roles in epileptogenesis.

Nyap1 Regulates Multipolar-Bipolar Transition and Morphology of Migrating Neurons by Fyn Phosphorylation during Corticogenesis

The coordination of cytoskeletal regulation is a prerequisite for proper neuronal migration during mammalian corticogenesis. Neuronal tyrosine-phosphorylated adaptor for the phosphoinositide 3-kinase 1 (Nyap1) is a member of the Nyap family of phosphoproteins, which has been studied in neuronal morphogenesis and is involved in remodeling of the actin cytoskeleton. However, the precise role of Nyap1 in neuronal migration remains unknown. Here, overexpression and knockdown of Nyap1 in the embryonic neocortex of mouse by in utero electroporation-induced abnormal morphologies and multipolar-bipolar transitions of migrating neurons. The level of phosphorylated Nyap1 was crucial for neuronal migration and morphogenesis in neurons. Furthermore, Nyap1 regulated neuronal migration as a downstream target of Fyn, a nonreceptor protein-tyrosine kinase that is a member of the Src family of kinases. Importantly, Nyap1 mediated the role of Fyn in the multipolar-bipolar transition of migrating neurons. Taken together, these results suggest that cortical radial migration is regulated by a molecular hierarchy of Fyn via Nyap1.

An Autism-Related, Nonsense Foxp1 Mutant Induces Autophagy and Delays Radial Migration of the Cortical Neurons

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that has a strong genetic component. Disruptions of FOXP1, a transcription factor expressed in the developing cerebral cortex, were associated with ASD. FOXP1(R525X) is a de novo heterozygous mutation found in patients with autism and severe mental retardation. To explore the neuronal basis of FOXP1(R525X) in ASD, we created Foxp1(R521X), a mouse homolog of the human variant. Ectopic expression of Foxp1(R521X) led to cytoplasmic aggregates and activated macroautophagy in neuroblastoma N2a cells and the developing neuronal cells. Cortical neurons expressing Foxp1(R521X) exhibited delayed migration and altered dendritic morphology. As a control, mutant Y435X that was expressed diffusively in the cytoplasm did not induce autophagy and migration delay in the cortex. The embryonic cortical cells had a minimal activity of nonsense-mediated mRNA decay (NMD) as assayed by a splicing-dependent NMD reporter. We hypothesize that the developing neuronal cells use autophagy but not NMD as a safeguard mechanism against nonsense mutant aggregates, resulting in impairment of the cortical development. This study suggests a novel mechanism other than heterozygous loss of FOXP1 for the development of ASD and may advance our understanding of the complex relationships between gene mutation and the related psychiatric disorders.

Ubiquitination status does not affect Vps34 degradation

Vps34 (vacuolar protein-sorting 34) plays important role in autophagy and endosomal trafficking. These processes are closely associated protein ubiquitination and degradation. We have hypothesized that Vps34 ubiquitination status would also control its degradation. Here, we report that our results did not support this assumption. In cells transiently transfected with ubiquitin (UB) constructs contained different lysine residues (Ks), Vps34 ubiquitination could occur regardless of the presence of any Ks in UB. However, Vps34 protein levels were not significantly altered in cells transiently transfected with these UB mutants. We further found that Vps34 protein was altered by pharmacological manipulation of E2/E3 activity; yet this effect was not significantly affected by UB overexpression. In vivo experiments revealed that in APP/PS1 mice, an animal model of Alzheimer's disease (AD), although ubiquitination of Vps34 was significantly reduced, Vps34 protein levels remained unchanged. Vps34 indeed was subjected to proteasomal or lysosomal degradation, as prolonged treatment of proteasomal inhibitor MG132 or lysosomal inhibitor chloroquine elevated Vps34 protein levels. We conclude that unlike most of other proteins, Vps34 ubiquitination is not closely associated with its degradation.

On the Role of Basal Autophagy in Adult Neural Stem Cells and Neurogenesis

Adult neurogenesis persists in the adult mammalian brain due to the existence of neural stem cell (NSC) reservoirs in defined niches, where they give rise to new neurons throughout life. Recent research has begun to address the implication of constitutive (basal) autophagy in the regulation of neurogenesis in the mature brain. This review summarizes the current knowledge on the role of autophagy-related genes in modulating adult NSCs, progenitor cells and their differentiation into neurons. The general function of autophagy in neurogenesis in several areas of the embryonic forebrain is also revisited. During development, basal autophagy regulates Wnt and Notch signaling and is mainly required for adequate neuronal differentiation. The available data in the adult indicate that the autophagy-lysosomal pathway regulates adult NSC maintenance, the activation of quiescent NSCs, the survival of the newly born neurons and the timing of their maturation. Future research is warranted to validate the results of these pioneering studies, refine the molecular mechanisms underlying the regulation of NSCs and newborn neurons by autophagy throughout the life-span of mammals and provide significance to the autophagic process in adult neurogenesis-dependent behavioral tasks, in physiological and pathological conditions. These lines of research may have important consequences for our understanding of stem cell dysfunction and neurogenic decline during healthy aging and neurodegeneration.

The physiological roles of autophagy in the mammalian life cycle

Autophagy is primarily an efficient intracellular catabolic pathway used for degradation of abnormal cellular protein aggregates and damaged organelles. Although autophagy was initially proposed to be a cellular stress responder, increasing evidence suggests that it carries out normal physiological roles in multiple biological processes. To date, autophagy has been identified in most organs and at many different developmental stages, indicating that it is not only essential for cellular homeostasis and renovation, but is also important for organ development. Herein, we summarize our current understanding of the functions of autophagy (which here refers to macroautophagy) in the mammalian life cycle.