Amyloid-β-stimulated plasminogen activation by tissue-type plasminogen activator results in processing of neuroendocrine factors

Upregulation of Proteolytic Pathways and Altered Protein Biosynthesis Underlie Retinal Pathology in a Mouse Model of Alzheimer's Disease

Increased amyloid β (Aβ) aggregation is a hallmark feature of Alzheimer's disease (AD) pathology. The APP/PS1 mouse model of AD exhibits accumulation of Aβ in the retina and demonstrates reduced retinal function and other degenerative changes. The overall molecular effects of AD pathology on the retina remain undetermined. Using a proteomics approach, this study assessed the molecular effects of Aβ accumulation and progression of AD pathology on the retina. Retinal tissues from younger (2.5 months) and older 8-month APP/PS1 mice were analysed for protein expression changes. A multiplexed proteomics approach using chemical isobaric tandem mass tags was applied followed by functional and protein-protein interaction analyses using Ingenuity pathway (IPA) and STRING computational tools. We identified approximately 2000 proteins each in the younger (upregulated 50; downregulated 36) and older set of APP/PS1 (upregulated 85; downregulated 79) mice retinas. Amyloid precursor protein (APP) was consistently upregulated two to threefold in both younger and older retinas (p < 0.0001). Mass spectrometry data further revealed that older APP/PS1 mice retinas had elevated levels of proteolytic enzymes cathepsin D, presenilin 2 and nicastrin that are associated with APP processing. Increased levels of proteasomal proteins Psma5, Psmd3 and Psmb2 were also observed in the older AD retinas. In contrast to the younger animals, significant downregulation of protein synthesis and elongation associated proteins such as Eef1a1, Rpl35a, Mrpl2 and Eef1e1 (p < 0.04) was identified in the older mice retinas. This study reports for the first time that not only old but also young APP/PS1 animals demonstrate increased amyloid protein levels in their retinas. Quantitative proteomics reveals new molecular insights which may represent a cellular response to clear amyloid build-up. Further, downregulation of ribosomal proteins involved in protein biosynthesis was observed which might be considered a toxicity effect.

What drives “fibrinolysis”?

The timely removal of blood clots and fibrin deposits is essential in the regulation of haemostasis. This is achieved by the fibrinolytic system, an enzymatic process that regulates the activation of plasminogen into its proteolytic form, plasmin. This is a self-regulated event as the very presence of fibrin initiates plasminogen activation on the fibrin surface due to the presentation of exposed C-terminal lysine residues in fibrin that allow plasminogen to position itself via its lysine binding sites and to be more efficiently cleaved by tissue-type plasminogen activator (t-PA). Hence fibrin, the ultimate substrate of plasmin during fibrinolysis, is indeed an essential cofactor in the cascade. What has now come to light is that the fibrinolytic system is not solely designed to eliminate fibrin. Indeed, it is a broad acting system that processes a variety of proteins, including many in the brain where there is no fibrin. So what drives t-PA-mediated plasminogen activation when fibrin is not available?

This review will describe the broadening role of the fibrinolytic system highlighting the importance of fibrin and other key proteins as facilitators during t-PA-mediated plasminogen activation.

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

Neuropeptides in depression: role of VGF

The monoamine hypothesis of depression is increasingly called into question by newer theories that revolve around changes in neuronal plasticity, primarily in the hippocampus, at both the structural and the functional levels. Chronic stress negatively regulates hippocampal function while antidepressants ameliorate the effects of stress on neuronal morphology and activity. Both stress and antidepressants have been shown to affect levels of brain-derived neurotrophic factor (BDNF) whose transcription is dependent on cAMP response element binding protein (CREB). BDNF itself has antidepressant-like actions and can induce transcription of a number of molecules. One class of genes regulated by both BDNF and serotonin (5-HT) are neuropeptides including VGF (non-acryonimic) which has a novel role in depression. Neuropeptides are important modulators of neuronal function but their role in affective disorders is just emerging. Recent studies demonstrate that VGF, which is also a CREB-dependent gene, is upregulated by antidepressant drugs and voluntary exercise and is reduced in animal models of depression. VGF enhances hippocampal synaptic plasticity as well as neurogenesis in the dentate gyrus but the mechanisms of antidepressant-like actions of VGF in behavioral paradigms are not known. We summarize experimental data describing the roles of BDNF, VGF and other neuropeptides in depression and how they may be acting through the generation of new neurons and altered synaptic activity. Understanding the molecular and cellular changes that underlie the actions of neuropeptides and how these adaptations result in antidepressant-like effects will aid in developing drugs that target novel pathways for major depressive disorders.

Molecular and cellular aspects of protein misfolding and disease

Proteins are essential elements for life. They are building blocks of all organisms and the operators of cellular functions. Humans produce a repertoire of at least 30,000 different proteins, each with a different role. Each protein has its own unique sequence and shape (native conformation) to fulfill its specific function. The appearance of incorrectly shaped (misfolded) proteins occurs on exposure to environmental changes. Protein misfolding and the subsequent aggregation is associated with various, often highly debilitating, diseases for which no sufficient cure is available yet. In the first part of this review we summarize the structural composition of proteins and the current knowledge of underlying forces that lead proteins to lose their native structure. In the second and third parts we describe the molecular and cellular mechanisms that are associated with protein misfolding in disease. Finally, in the last part we portray recent efforts to develop treatments for protein misfolding diseases.

The role of the vgf gene and VGF-derived peptides in nutrition and metabolism

Energy homeostasis is a complex physiological function coordinated at multiple levels. The issue of genetic regulation of nutrition and metabolism is attracting increasing interest and new energy homeostasis-regulatory genes are continuously identified. Among these genes, vgf is gaining increasing interest following two observations: (1) VGF-/- mice have a lean and hypermetabolic phenotype; (2) the first VGF-derived peptide involved in energy homeostasis, named TLQP-21, has been identified. The aim of this review will be to discuss the role of the vgf gene and VGF derived peptides in metabolic and nutritional functions. In particular we will: (1) provide a brief overview on the central systems regulating energy homeostasis and nutrition particularly focusing on the melanocortin system; (2) introduce the structure and molecular characteristic of vgf; (3) describe the phenotype of VGF deficient mice; (4) present recent data on the metabolic role of VGF-derived peptides, particularly focusing on one peptide named TLQP-21.

The urokinase-type plasminogen activator polymorphism PLAU_1 is a risk factor for APOE-ε4 non-carriers in the Italian Alzheimer’s disease population and does not affect the plasma Aβ(1–42) level

Sporadic Alzheimer's disease (AD) is the most frequent form of dementia in the elderly. A non-conservative polymorphism in the urokinase-type plasminogen activator gene (PLAU_1=RS2227564) has been analyzed, but data are conflicting on whether it is a risk factor for AD. To clarify whether this genetic variant modifies AD risk in the Italian population, we ran a case-control association study on 192 AD and 126 age-matched controls. We did not find any association between PLAU_1 genotype and AD in the whole AD population, but when we stratified our sample by APOE-epsilon4 status, we found a significant association between PLAU_1 genotype (C/T+T/T) and APOE-epsilon4 negative AD subjects (p=0.02, chi(2)-test). The PLAU_1 genotype did not appear to affect the plasma Abeta42 concentration. Our data support a role for PLAU_1 as an independent genetic risk factor for AD in the Italian population for those subjects who do not have the APOE-epsilon4 allele.