Neuronal protein 22 colocalises with both the microtubule and microfilament cytoskeleton in neurite-like processes

Biochemical Features and Physiological Roles of hNP22 in the Central Nervous System

hNP22, a novel neuron-specific protein that interacts with both actin filaments and microtubules, was found to be highly homologous to the smooth muscle cell cytoskeleton-associated proteins human SM22α and rat acidic calponin. In recent years, functions of hNP22 such as the promotion of neural differentiation and enhancement of neural plasticity, have been described, as well as potential roles of hNP22 in schizophrenia and alcohol-related brain damage (ARBD). Because of the potential roles of hNP22 in neuronal processes and its potential implications in diseases, hNP22 has emerged as a research target. In this paper, we review the gene structure, possible modifications, and functions of the hNP22 protein, as well as its potential clinical significance. Based on its physical structure and previous studies, we speculate that hNP22 has potential biological functions in neurological disorders, such as schizophrenia and ARBD.

The Interplay between Retinal Pathways of Cholesterol Output and Its Effects on Mouse Retina

In mammalian retina, cholesterol excess is mainly metabolized to oxysterols by cytochromes P450 27A1 (CYP27A1) and 46A1 (CYP46A1) or removed on lipoprotein particles containing apolipoprotein E (APOE). In contrast, esterification by sterol-O-acyltransferase 1 (SOAT) plays only a minor role in this process. Accordingly, retinal cholesterol levels are unchanged in Soat1^-/- mice but are increased in Cyp27a1^-/-Cyp46a1^-/- and Apoe^-/- mice. Herein, we characterized Cyp27a1^-/-Cyp46a1^-/-Soat1^-/- and Cyp27a1^-/-Cyp46a1^-/-Apoe^-/- mice. In the former, retinal cholesterol levels, anatomical gross structure, and vasculature were normal, yet the electroretinographic responses were impaired. Conversely, in Cyp27a1^-/-Cyp46a1^-/-Apoe^-/- mice, retinal cholesterol levels were increased while anatomical structure and vasculature were unaffected with only male mice showing a decrease in electroretinographic responses. Sterol profiling, qRT-PCR, proteomics, and transmission electron microscopy mapped potential compensatory mechanisms in the Cyp27a1^-/-Cyp46a1^-/-Soat1^-/- and Cyp27a1^-/-Cyp46a1^-/-Apoe^-/- retina. These included decreased cholesterol biosynthesis along with enhanced formation of intra- and extracellular vesicles, possibly a reserve mechanism for lowering retinal cholesterol. In addition, there was altered abundance of proteins in Cyp27a1^-/-Cyp46a1^-/-Soat1^-/- mice that can affect photoreceptor function, survival, and retinal energy homeostasis (glucose and fatty acid metabolism). Therefore, the levels of retinal cholesterol do not seem to predict retinal abnormalities, and it is rather the network of compensatory mechanisms that appears to determine retinal phenotype.

Identification of genome-wide SNP-SNP and SNP-clinical Boolean interactions in age-related macular degeneration

We propose here a methodology to uncover modularities in the network of SNP-SNP interactions most associated with disease. We start by computing all possible Boolean binary SNP interactions across the whole genome. By constructing a weighted graph of the most relevant interactions and via a combinatorial optimization approach, we find the most highly interconnected SNPs. We show that the method can be easily extended to find SNP/environment interactions. Using a modestly sized GWAS dataset of age-related macular degeneration (AMD), we identify a group of only 19 SNPs, which include those in previously reported regions associated to AMD. We also uncover a larger set of loci pointing to a matrix of key processes and functions that are affected. The proposed integrative methodology extends and overlaps traditional statistical analysis in a natural way. Combinatorial optimization techniques allow us to find the kernel of the most central interactions, complementing current methods of GWAS analysis and also enhancing the search for gene-environment interaction.

A proteomic analysis of the ventral hippocampus of rats subjected to maternal separation and escitalopram treatment

Early life stress is known to predispose humans to the development of depression. Developmental stress has been shown to cause various changes in neurotransmitter systems, neurotrophin expression and the hypothalamic pituitary adrenal-axis in the rat brain. The aim of this study was to identify which cytosolic proteins are altered by maternal separation, as a model for depression, as well as by chronic antidepressant treatment. Rats were maternally separated from postnatal day 2-14 for 3 h per day while control rats were normally reared. Both groups were divided and received either escitalopram or saline injections for 6 weeks starting from postnatal day 40. The ventral hippocampal tissue was fractionated and the cytosolic fraction used for 2-D-gel electrophoresis and liquid chromatography coupled to mass spectrometry analyses to identify peptides. Mascot database searches were done to identify proteins that were differentially expressed between the groups. Proteins that were significantly changed by maternal separation included amongst others: molecular chaperones and proteins related to energy metabolism; neuroplasticity; oxidative stress regulation; and protein metabolism. Treatment with escitalopram, a selective-serotonin reuptake inhibitor, induced changes in a different group of proteins, except for a few involved in energy metabolism and neuroprotective pathways. The results indicate which cytosolic proteins are changed by early life stress and may therefore be involved in the development of depression.

A function for the calponin family member NP25 in neurite outgrowth

The neuronal protein 25 (NP25), a member of the calponin (CaP) protein family, has previously been identified as neuron-specific protein in the adult rat brain. Here, we show an early onset of NP25 expression in the chick embryo neural tube. NP25 represents, together with NeuroM, one of the earliest markers for postmitotic neurons. To elucidate its function in the developing nervous system, NP25 was overexpressed in E5 and E9 sensory neurons, E7 sympathetic neurons and PC12 cells that show different endogenous NP25 expression levels. Whereas E5 and E9 sensory neurons and PC12 cells, which express low endogenous levels of NP25, responded by enhanced neurite outgrowth, a reduction of neurite length was observed in sympathetic neurons, which already express high endogenous levels of NP25. Knockdown of NP25 in sensory neurons using NP25 siRNA resulted in shorter neurites, whereas reduction of NP25 expression in sympathetic neurons led to increased neurite length. These results suggest a dynamic function for NP25 in the regulation of neurite growth, with an optimal level of NP25 required for maximal growth.

Cytoskeleton proteins are modulators of mutant tau-induced neurodegeneration in Drosophila

Tauopathies, including Alzheimer's disease and fronto-temporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), are a group of neurodegenerative disorders characterized by the presence of intraneuronal filamentous inclusions of aberrantly phosphorylated-tau. Tau is a neuronal microtubule-associated protein involved in microtubule assembly and stabilization. Currently, the molecular mechanisms underlying tau-mediated cellular toxicity remain elusive. To address the determinants of tau neurotoxicity, we first characterized the cellular alterations resulting from the over-expression of a mutant form of human tau associated with FTDP-17 (tau V337M) in Drosophila. We found that the over-expression of tau V337M, in Drosophila larval motor neurons, induced disruption of the microtubular network at presynaptic nerve terminals and changes in neuromuscular junctions morphological features. Secondly, we performed a misexpression screen to identify genetic modifiers of the tau V337M-mediated rough eye phenotype. The screening of 1250 mutant Drosophila lines allowed us to identify several components of the cytoskeleton, and particularly from the actin network, as specific modifiers of tau V337M-induced neurodegeneration. Furthermore, we found that numerous tau modulators identified in our screen were involved in the maintenance of synaptic function. Taken together, these findings suggest that disruption of the microtubule network in presynaptic nerve terminals could constitute early events in the pathological process leading to synaptic dysfunction in tau V337M pathology.