Fibronectin-integrin signaling regulates PLVAP localization at endothelial fenestrae by microtubule stabilization.

Endothelial fenestrae are the transcellular pores existing on the capillary walls which are organized in clusters referred to as sieve plates. They are also divided by a diaphragm consisting of plasmalemma vesicle-associated protein (PLVAP). In this study, we examined the involvement of fibronectin signaling in the formation of fenestra and diaphragm in endothelial cells. Results showed that Itga5 and Itgb1 were expressed in PECAM1-positive endothelial cells isolated from the anterior lobe (AL) of the rat pituitary, and integrin α5 was localized at the fenestrated capillaries of the rat pituitary and cultured PECAM1-positive endothelial cells isolated from AL (CECAL). Inhibition of both integrin α5ß1 and FAK, a key molecule for integrin-microtubule signaling, respectively, by ATN-161 and FAK inhibitor 14, caused the delocalization of PLVAP at the sieve plates and depolymerization of microtubules in CECAL. Paclitaxel prevented the delocalization of PLVAP by the inhibition of integrin α5ß1. Microtubule depolymerization induced by colcemid also caused the delocalization of PLVAP. Treatment of CECAL with ATN-161 and colcemid caused PLVAP localization at the Golgi apparatus. The localization of PLVAP at the sieve plates was inhibited by BFA treatment in a time-dependent manner and spread diffusely to the cytoplasm. These results indicate that a constant supply of PLVAP proteins by the endomembrane system via the Golgi apparatus is essential for the localization of PLVAP at sieve plates. In conclusion, the endomembrane transport pathway from the Golgi apparatus to sieve plates requires microtubule cytoskeletons, which are regulated by fibronectin-integrin α5ß1 signaling.

Fibronectin is essential for formation of fenestrae in endothelial cells of the fenestrated capillary.

Endothelial fenestrae are transcellular pores that pierce the capillary walls in endocrine glands such as the pituitary. The fenestrae are covered with a thin fibrous diaphragm consisting of the plasmalemma vesicle-associated protein (PLVAP) that clusters to form sieve plates. The basal surface of the vascular wall is lined by basement membrane (BM) composed of various extracellular matrices (ECMs). However, the relationship between the ECMs and the endothelial fenestrae is still unknown. In this study, we isolated fenestrated endothelial cells from the anterior lobe of the rat pituitary, using a dynabeads-labeled antibody against platelet endothelial cell adhesion molecule 1 (PECAM1). We then analyzed the gene expression levels of several endothelial marker genes and genes for integrin α subunits, which function as the receptors for ECMs, by real-time polymerase chain reaction (PCR). The results showed that the genes for the integrin α subunit, which binds to collagen IV, fibronectin, laminin-411, or laminin-511, were highly expressed. When the PECAM1-positive cells were cultured for 7 days on collagen IV-, fibronectin-, laminins-411-, or laminins-511-coated coverslips, the sieve plate structures equipped with probably functional fenestrae were maintained only when the cells were cultured on fibronectin. Additionally, real-time PCR analysis showed that the fibronectin coating was effective in maintaining the expression pattern of several endothelial marker genes that were preferentially expressed in the endothelial cells of the fenestrated capillaries. These results indicate that fibronectin functions as the principal factor in the maintenance of the sieve plate structures in the endothelial cells of the fenestrated capillary.

Role of tubulin acetylation in cellular functions and diseases.

Acetylation is a well-studied post-translational modification (PTM) of tubulin. Acetylated tubulin is present in the centrioles, primary cilia, and flagella, which contain long-lived stable microtubules. Tubulin acetylation plays an important role in cellular activities including cell polarity, cell migration, vesicle transport, and cell development. Cryo-electron microscopy reconstructions have revealed conformational changes in acetylated tubulin, revealing a reduction in intermonomer interactions among tubulins and an increase in microtubule elasticity. The kinetics of conformational changes in acetylated tubulin may elucidate microtubule functions in these cellular activities. Abnormal tubulin acetylation has been implicated in neurodegenerative disorders, ciliopathies, and cancers. Thus, it is important to elucidate the mechanisms underlying tubulin acetylation and its effects on cellular activity to understand these diseases and to design potential therapeutic strategies. This review discusses the cellular distribution and dynamics of acetylated tubulin and its role in regulating cellular activities.

GABARAPs dysfunction by autophagy deficiency in adolescent brain impairs GABAA receptor trafficking and social behavior.

Dysfunctional mTOR signaling is associated with the pathogenesis of neurodevelopmental and neuropsychiatric disorders. However, it is unclear what molecular mechanisms and pathogenic mediators are involved and whether mTOR-regulated autophagy continues to be crucial beyond neurodevelopment. Here, we selectively deleted Atg7 in forebrain GABAergic interneurons in adolescent mice and unexpectedly found that these mice showed a set of behavioral deficits similar to Atg7 deletion in forebrain excitatory neurons. By unbiased quantitative proteomic analysis, we identified γ-aminobutyric acid receptor-associated protein-like 2 (GABARAPL2) to differentially form high-molecular weight species in autophagy-deficient brains. Further functional analyses revealed a novel pathogenic mechanism involving the p62-dependent sequestration of GABARAP family proteins, leading to the reduction of surface GABAA receptor levels. Our work demonstrates a novel physiological role for autophagy in regulating GABA signaling beyond postnatal neurodevelopment, providing a potential mechanism for the reduced inhibitory inputs observed in neurodevelopmental and neuropsychiatric disorders with mTOR hyperactivation.

Dynamic localization of α-tubulin acetyltransferase ATAT1 through the cell cycle in human fibroblastic KD cells.

Acetylation of α-tubulin is a well-studied posttranscriptional modification, which is mostly catalyzed by α-tubulin N-acetyltransferase (ATAT1). ATAT1 possibly affects various cellular functions related with microtubules, such as intracellular transport, cell motility, cilia formation, and neuronal signaling. Here, we analyzed the subcellular localization of immunolabeled ATAT1 in human fibroblast KD cells through the cell cycle using confocal laser scanning microscopy. ATAT1 dramatically changed its localization through the cell cycle, depending on the mitotic phase. In interphase, immunolabeled ATAT1 was observed in centrioles, nuclei, and basal bodies if the cells projected primary cilia. ATAT1 was intensely detected as clusters in the nuclei in the G1-G2 phase. In telophase, ATAT1 colocalized with chromatids and spindle poles, and ultimately migrated to the daughter nucleus, newly synthesized centrioles, and midbody. The nucleolus is a core region of ribosomal RNA transcription, and the midbody is associated with severing and depolymerizing of microtubules in the stembody. The specific distributions of ATAT1 through the cell cycle suggest multiple functions of ATAT1, which could include acetylation of microtubules, RNA transcription activity, severing microtubules, and completion of cytokinesis.

TAR DNA-Binding Protein 43 and Disrupted in Schizophrenia 1 Coaggregation Disrupts Dendritic Local Translation and Mental Function in Frontotemporal Lobar Degeneration.

BACKGROUND: Neurodegenerative diseases involving protein aggregation often accompany psychiatric symptoms. Frontotemporal lobar degeneration (FTLD) associated with TAR DNA-binding protein 43 (TDP-43) aggregation is characterized by progressive neuronal atrophy in frontal and temporal lobes of cerebral cortex. Furthermore, patients with FTLD display mental dysfunction in multiple behavioral dimensions. Nevertheless, their molecular origin for psychiatric symptoms remains unclear. METHODS: In FTLD neurons and mouse models with TDP-43 aggregates, we examined coaggregation between TDP-43 and disrupted in schizophrenia 1 (DISC1), a key player in the pathology of mental conditions and its effects on local translation in dendrites and psychiatric behaviors. The protein coaggregation and the expression level of synaptic proteins were also investigated with postmortem brains from patients with FTLD (n = 6). RESULTS: We found cytosolic TDP-43/DISC1 coaggregates in brains of both FTLD mouse model and patients with FTLD. At the mechanistic levels, the TDP-43/DISC1 coaggregates disrupted the activity-dependent dendritic local translation through impairment of translation initiation and, in turn, reduced synaptic protein expression. Behavioral deficits detected in FTLD model mice were ameliorated by exogenous DISC1 expression. CONCLUSIONS: Our findings reveal a novel role of the aggregate-prone TDP-43/DISC1 protein complex in regulating local translation, which affects aberrant behaviors relevant to multiple psychiatric dimensions.

ATAT1 is essential for regulation of homeostasis-retaining cellular responses in corticotrophs along hypothalamic-pituitary-adrenal axis.

The production and secretion of adrenocorticotropin, a proopiomelanocortin (POMC)-derived hormone, by corticotrophs in the anterior pituitary, is regulated by corticotrophin-releasing hormone (CRH) and glucocorticoids. We have previously demonstrated that adrenalectomy induces α-tubulin N-acetyltransferase 1 (ATAT1) expression and α-tubulin acetylation in corticotrophs. However, the regulatory mechanism of ATAT1 expression and the function of acetylated microtubules in corticotrophs are unclear. Here, we analyze the effect of CRH or dexamethasone on Atat1 expression in the mouse corticotroph AtT20 cell line. The expression of Atat1 was increased by CRH and decreased by dexamethasone in AtT20 cells. We examined the effect of Atat1 knockdown on the expression of POMC-associated genes and the dexamethasone-induced nuclear translocation of glucocorticoid receptor (GR) by real-time polymerase chain reaction and Western blot analysis, respectively. Atat1 knockdown resulted in a significant increase in the expression of ACTH-producing genes and decreased the dexamethasone-induced nuclear translocation of GR accompanied with a reduction in α-tubulin acetylation. Atat1 overexpression resulted in a significant increase in α-tubulin acetylation and the dexamethasone-induced nuclear translocation of GR. These results suggest that the acetylated microtubules function as the rail-line for the transportation of GR into the nucleus. We conclude that ATAT1 finely tunes the cellular responses of corticotrophs to hormonal stimulation through an intracellular feedback circuit.

Aggregation of scaffolding protein DISC1 dysregulates phosphodiesterase 4 in Huntington's disease.

Huntington's disease (HD) is a polyglutamine (polyQ) disease caused by aberrant expansion of the polyQ tract in Huntingtin (HTT). While motor impairment mediated by polyQ-expanded HTT has been intensively studied, molecular mechanisms for nonmotor symptoms in HD, such as psychiatric manifestations, remain elusive. Here we have demonstrated that HTT forms a ternary protein complex with the scaffolding protein DISC1 and cAMP-degrading phosphodiesterase 4 (PDE4) to regulate PDE4 activity. We observed pathological cross-seeding between DISC1 and mutant HTT aggregates in the brains of HD patients as well as in a murine model that recapitulates the polyQ pathology of HD (R6/2 mice). In R6/2 mice, consequent reductions in soluble DISC1 led to dysregulation of DISC1-PDE4 complexes, aberrantly increasing the activity of PDE4. Importantly, exogenous expression of a modified DISC1, which binds to PDE4 but not mutant HTT, normalized PDE4 activity and ameliorated anhedonia in the R6/2 mice. We propose that cross-seeding of mutant HTT and DISC1 and the resultant changes in PDE4 activity may underlie the pathology of a specific subset of mental manifestations of HD, which may provide an insight into molecular signaling in mental illness in general.

Expression and localization of forkhead box protein FOXJ1 in S100ß-positive multiciliated cells of the rat pituitary.

S100ß-positive cells exist in the marginal cell layer (MCL) of the adenohypophysis and follicle structure in the parenchyma of anterior lobe (ALFS) in pituitary. They have multiple functions as phagocytes or cells that regulate hormone secretion. Majority of S100ß-positive cells in the adenohypophysis express sex determining region Y-box 2 protein (SOX2), a stem cell marker; therefore, S100ß/SOX2 double positive cells are also considered as one type of stem/progenitor cells. MCL and ALFS are consisting of morphologically two types of cells, i.e., multiciliated cells and non-ciliated cells. However, the relationship between the S100ß-positive cells and multiciliated cells in the pituitary is largely unknown. In the present study, we first immunohistochemically verified the feature of multiciliated cells in MCL and ALFS. We then examined the expression patterns of FOXJ1, an essential expression factor for multiciliated cell-differentiation, and SOX2 in the S100ß-positive multiciliated cells by in situ hybridization and immunohistochemistry. We identified anew the S100ß/SOX2/FOXJ1 triple positive multiciliated cells, and revealed that they were dispersed throughout the MCL and ALFS. These results indicate that the MCL and ALFS are consisting of morphologically and functionally distinct two types of cells, i.e., S100ß/SOX2 double positive non-ciliated cells and S100ß/SOX2/FOXJ1 triple positive multiciliated cells.

Aging causes distinct characteristics of polyglutamine amyloids in vivo.

Polyglutamine diseases, including Machado-Joseph disease and Huntington's disease, typically appear in midlife and are characterized by amyloid accumulations of abnormally expanded polyglutamine proteins. Although there is growing evidence that aging has an important role in the occurrence of such diseases, the role of aging in the late onset of these diseases is not well understood. Recent studies showed that differences in amyloid conformation from different brain regions lead to differing toxicity. We hypothesized that higher amyloid toxicity at later ages might cause the late onset of polyglutamine diseases. Using a method for temporal and regional gene expression targeting (TARGET) in Drosophila, we showed that transient polyglutamine expression caused more severe neurodegeneration in older flies than in younger flies. Moreover, the polyglutamine amyloids themselves showed distinct characteristics in relation to age; those from older flies were less resistant to SDS and more effective at seeding polymerization than those from younger flies, suggesting that the polyglutamine amyloids in aged individuals may have higher toxicity. These findings show that age-related changes in amyloid characteristics may be a trigger for late-onset polyglutamine diseases.

Distinct conformations of in vitro and in vivo amyloids of huntingtin-exon1 show different cytotoxicity.

A hallmark of polyglutamine diseases, including Huntington disease (HD), is the formation of beta-sheet-rich aggregates, called amyloid, of causative proteins with expanded polyglutamines. However, it has remained unclear whether the polyglutamine amyloid is a direct cause or simply a secondary manifestation of the pathology. Here we show that huntingtin-exon1 (thtt) with expanded polyglutamines remarkably misfolds into distinct amyloid conformations under different temperatures, such as 4 degrees C and 37 degrees C. The 4 degrees C amyloid has loop/turn structures together with mostly beta-sheets, including exposed polyglutamines, whereas the 37 degrees C amyloid has more extended and buried beta-sheets. By developing a method to efficiently introduce amyloid into mammalian cells, we found that the formation of the 4 degrees C amyloid led to substantial toxicity, whereas the toxic effects of the 37 degrees C amyloid were very small. Importantly, thtt amyloids in different brain regions of HD mice also had distinct conformations. The thermolabile thtt amyloid with loop/turn structures in the striatum showed higher toxicity, whereas the rigid thtt amyloid with more extended beta-sheets in the hippocampus and cerebellum had only mild toxic effects. These studies show that the thtt protein with expanded polyglutamines can misfold into distinct amyloid conformations and, depending on the conformations, the amyloids can be either toxic or nontoxic. Thus, the amyloid conformation of thtt may be a critical determinant of cytotoxicity in HD.