Residue Interaction Network Analysis Predicts a Val24-Ile31 Interaction May be Involved in Preventing Amyloid-Beta (1-42) Primary Nucleation.

Alzheimer's disease (AD) patients could benefit from a more effective treatment than the current FDA-approved options. Because amyloid-beta (Aß) is thought to play a central role in AD pathogenesis, many experimental drugs attempt to reduce Aß-induced pathology. Preventing amyloid accumulation may be a more effective strategy than clearing Aß plaques after they form. If preventing Aß accumulation can treat or prevent AD, then understanding Aß primary nucleation may aid rational drug design. This study examines Aß residue interaction networks and reports network and structural observations that may provide insight into primary nucleation. While many studies identify structural features of Aß that promote aggregation, this study reports features that may resist primary nucleation by examining Aß42 studies in more and less polar solvents. In Aß42 in a less polar solvent (PDB ID: 1IYT), Val24 and Ile31 have higher betweenness and residue centrality values. This may be due to a predicted interaction between Val24 and Ile31. Residues in the central hydrophobic cluster (CHC) of Aß40 and Aß42 had significantly higher betweenness values compared to the average betweenness of the structures, highlighting the CHC's reported role in oligomerization. The predicted interaction between Val24 and Ile31 may reduce the likelihood of primary nucleation of Aß.

SARS-CoV and SARS-CoV-2 main protease residue interaction networks change when bound to inhibitor N3.

COVID-19 is a respiratory disease caused by the coronavirus SARS-CoV-2. SARS-CoV-2 has many similarities with SARS-CoV. Both viruses rely on a protease called the main protease, or Mpro, for replication. Therefore, inhibiting Mpro may be a successful strategy for treating COVID-19. Structures of the main proteases of SARS-CoV and SARS-CoV-2 with and without inhibitor N3 are available in the Protein Data Bank. Comparing these structures revealed residue interaction network changes associated with N3 inhibition. Comparing network clustering with and without inhibitor N3 identified the formation of a cluster of residues 17, 18, 30-33, 70, 95, 98, 103, 117, 122, and 177 as a network change in both viral proteases when bound to inhibitor N3. Betweenness and stress centrality differences as well as differences in bond energies and relative B-factors when comparing free Mpro to inhibitor-bound Mpro identified residues 131, 175, 182, and 185 as possibly conformationally relevant when bound to the inhibitor N3. Taken together, these results provide insight into conformational changes of betacoronavirus Mpros when bound to an inhibitor.

Effects of a high protein diet and liver disease in an in silico model of human ammonia metabolism.

BACKGROUND: After proteolysis, the majority of released amino acids from dietary protein are transported to the liver for gluconeogenesis or to peripheral tissues where they are used for protein synthesis and eventually catabolized, producing ammonia as a byproduct. High ammonia levels in the brain are a major contributor to the decreased neural function that occurs in several pathological conditions such as hepatic encephalopathy when liver urea cycle function is compromised. Therefore, it is important to gain a deeper understanding of human ammonia metabolism. The objective of this study was to predict changes in blood ammonia levels resulting from alterations in dietary protein intake, from liver disease, or from partial loss of urea cycle function. METHODS: A simple mathematical model was created using MATLAB SimBiology and data from published studies. Simulations were performed and results analyzed to determine steady state changes in ammonia levels resulting from varying dietary protein intake and varying liver enzyme activity levels to simulate liver disease. As a toxicity reference, viability was measured in SH-SY5Y neuroblastoma cells following differentiation and ammonium chloride treatment. RESULTS: Results from control simulations yielded steady state blood ammonia levels within normal physiological limits. Increasing dietary protein intake by 72% resulted in a 59% increase in blood ammonia levels. Simulations of liver cirrhosis increased blood ammonia levels by 41 to 130% depending upon the level of dietary protein intake. Simulations of heterozygous individuals carrying a loss of function allele of the urea cycle carbamoyl phosphate synthetase I (CPS1) gene resulted in more than a tripling of blood ammonia levels (from roughly 18 to 60 µM depending on dietary protein intake). The viability of differentiated SH-SY5Y cells was decreased by 14% by the addition of a slightly higher amount of ammonium chloride (90 µM). CONCLUSIONS: Data from the model suggest decreasing protein consumption may be one simple strategy to decrease blood ammonia levels and minimize the risk of developing hepatic encephalopathy for many liver disease patients. In addition, the model suggests subjects who are known carriers of disease-causing CPS1 alleles may benefit from monitoring blood ammonia levels and limiting the level of protein intake if ammonia levels are high.

In silico prediction of novel residues involved in amyloid primary nucleation of human I56T and D67H lysozyme.

BACKGROUND: Amyloidogenic proteins are most often associated with neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, but there are more than two dozen human proteins known to form amyloid fibrils associated with disease. Lysozyme is an antimicrobial protein that is used as a general model to study amyloid fibril formation. Studies aimed at elucidating the process of amyloid formation of lysozyme tend to focus on partial unfolding of the native state due to the relative instability of mutant amyloidogenic variants. While this is well supported, the data presented here suggest the native structure of the variants may also play a role in primary nucleation. RESULTS: Three-dimensional structural analysis identified lysozyme residues 21, 62, 104, and 122 as displaced in both amyloidogenic variants compared to wild type lysozyme. Residue interaction network (RIN) analysis found greater clustering of residues 112-117 in amyloidogenic variants of lysozyme compared to wild type. An analysis of the most energetically favored predicted dimers and trimers provided further evidence for a role for residues 21, 62, 104, 122, and 112-117 in amyloid formation. CONCLUSIONS: This study used lysozyme as a model to demonstrate the utility of combining 3D structural analysis with RIN analysis for studying the general process of amyloidogenesis. Results indicated that binding of two or more amyloidogenic lysozyme mutants may be involved in amyloid nucleation by placing key residues (21, 62, 104, 122, and 112-117) in proximity before partial unfolding occurs. Identifying residues in the native state that may be involved in amyloid formation could provide novel drug targets to prevent a range of amyloidoses.

In Silico Preliminary Association of Ammonia Metabolism Genes GLS, CPS1, and GLUL with Risk of Alzheimer's Disease, Major Depressive Disorder, and Type 2 Diabetes.

Ammonia is a toxic by-product of protein catabolism and is involved in changes in glutamate metabolism. Therefore, ammonia metabolism genes may link a range of diseases involving glutamate signaling such as Alzheimer's disease (AD), major depressive disorder (MDD), and type 2 diabetes (T2D). We analyzed data from a National Institute on Aging study with a family-based design to determine if 45 single nucleotide polymorphisms (SNPs) in glutaminase (GLS), carbamoyl phosphate synthetase 1 (CPS1), or glutamate-ammonia ligase (GLUL) genes were associated with AD, MDD, or T2D using PLINK software. HAPLOVIEW software was used to calculate linkage disequilibrium measures for the SNPs. Next, we analyzed the associated variations for potential effects on transcriptional control sites to identify possible functional effects of the SNPs. Of the SNPs that passed the quality control tests, four SNPs in the GLS gene were significantly associated with AD, two SNPs in the GLS gene were associated with T2D, and one SNP in the GLUL gene and three SNPs in the CPS1 gene were associated with MDD before Bonferroni correction. The in silico bioinformatic analysis suggested probable functional roles for six associated SNPs. Glutamate signaling pathways have been implicated in all these diseases, and other studies have detected similar brain pathologies such as cortical thinning in AD, MDD, and T2D. Taken together, these data potentially link GLS with AD, GLS with T2D, and CPS1 and GLUL with MDD and stimulate the generation of testable hypotheses that may help explain the molecular basis of pathologies shared by these disorders.

Individual Amino Acid Supplementation Can Improve Energy Metabolism and Decrease ROS Production in Neuronal Cells Overexpressing Alpha-Synuclein.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by alpha-synuclein accumulation and loss of dopaminergic neurons in the substantia nigra (SN) region of the brain. Increased levels of alpha-synuclein have been shown to result in loss of mitochondrial electron transport chain complex I activity leading to increased reactive oxygen species (ROS) production. WT alpha-synuclein was stably overexpressed in human BE(2)-M17 neuroblastoma cells resulting in increased levels of an alpha-synuclein multimer, but no increase in alpha-synuclein monomer levels. Oxygen consumption was decreased by alpha-synuclein overexpression, but ATP levels did not decrease and ROS levels did not increase. Treatment with ferrous sulfate, a ROS generator, resulted in decreased oxygen consumption in both control and alpha-synuclein overexpressing cells. However, this treatment only decreased ATP levels and increased ROS production in the cells overexpressing alpha-synuclein. Similarly, paraquat, another ROS generator, decreased ATP levels in the alpha-synuclein overexpressing cells, but not in the control cells, further demonstrating how alpha-synuclein sensitized the cells to oxidative insult. Proteomic analysis yielded molecular insights into the cellular adaptations to alpha-synuclein overexpression, such as the increased abundance of many mitochondrial proteins. Many amino acids and citric acid cycle intermediates and their ester forms were individually supplemented to the cells with L-serine, L-proline, L-aspartate, or L-glutamine decreasing ROS production in oxidatively stressed alpha-synuclein overexpressing cells, while diethyl oxaloacetate or L-valine supplementation increased ATP levels. These results suggest that dietary supplementation with individual metabolites could yield bioenergetic improvements in PD patients to delay loss of dopaminergic neurons.

Amino Acid Catabolism in Alzheimer's Disease Brain: Friend or Foe?

There is a dire need to discover new targets for Alzheimer's disease (AD) drug development. Decreased neuronal glucose metabolism that occurs in AD brain could play a central role in disease progression. Little is known about the compensatory neuronal changes that occur to attempt to maintain energy homeostasis. In this review using the PubMed literature database, we summarize evidence that amino acid oxidation can temporarily compensate for the decreased glucose metabolism, but eventually altered amino acid and amino acid catabolite levels likely lead to toxicities contributing to AD progression. Because amino acids are involved in so many cellular metabolic and signaling pathways, the effects of altered amino acid metabolism in AD brain are far-reaching. Possible pathological results from changes in the levels of several important amino acids are discussed. Urea cycle function may be induced in endothelial cells of AD patient brains, possibly to remove excess ammonia produced from increased amino acid catabolism. Studying AD from a metabolic perspective provides new insights into AD pathogenesis and may lead to the discovery of dietary metabolite supplements that can partially compensate for alterations of enzymatic function to delay AD or alleviate some of the suffering caused by the disease.

Hepatitis C virus-induced myeloid-derived suppressor cells regulate T-cell differentiation and function via the signal transducer and activator of transcription 3 pathway.

T cells play a pivotal role in controlling viral infection; however, the precise mechanisms responsible for regulating T-cell differentiation and function during infections are incompletely understood. In this study, we demonstrated an expansion of myeloid-derived suppressor cells (MDSCs), in particular the monocytic MDSCs (M-MDSCs; CD14(+) CD33(+) CD11b(+) HLA-DR(-/low) ), in patients with chronic hepatitis C virus (HCV) infection. Notably, HCV-induced M-MDSCs express high levels of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) and interleukin-10 (IL-10) compared with healthy subjects. Blocking STAT3 signalling reduced HCV-mediated M-MDSC expansion and decreased IL-10 expression. Importantly, we observed a significant increase in the numbers of CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells following incubation of healthy peripheral blood mononuclear cells (PBMCs) with MDSCs derived from HCV-infected patients or treated with HCV core protein. In addition, depletion of MDSCs from PBMCs led to a significant reduction of Foxp3(+) Treg cells developed during chronic HCV infection. Moreover, depletion of MDSCs from PBMCs significantly increased interferon-γ production by CD4(+) T effector (Teff) cells derived from HCV patients. These results suggest that HCV-induced MDSCs promote Treg cell development and inhibit Teff cell function, suggesting a novel mechanism for T-cell regulation and a new strategy for immunotherapy against human viral diseases.

Hepatitis C virus-induced reduction in miR-181a impairs CD4(+) T-cell responses through overexpression of DUSP6.

UNLABELLED: T cells play a crucial role in viral clearance or persistence; however, the precise mechanisms that control their responses during viral infection remain incompletely understood. MicroRNA (miR) has been implicated as a key regulator controlling diverse biological processes through posttranscriptional repression. Here, we demonstrate that hepatitis C virus (HCV)-mediated decline of miR-181a expression impairs CD4(+) T-cell responses through overexpression of dual specific phosphatase 6 (DUSP6). Specifically, a significant decline of miR-181a expression along with overexpression of DUSP6 was observed in CD4(+) T cells from chronically HCV-infected individuals compared to healthy subjects, and the levels of miR-181a loss were found to be negatively associated with the levels of DUSP6 overexpression in these cells. Importantly, reconstitution of miR-181a or blockade of DUSP6 expression in CD4(+) T cells led to improved T-cell responses including enhanced CD25 and CD69 expression, increased interleukin-2 expression, and improved proliferation of CD4(+) T cells derived from chronically HCV-infected individuals. CONCLUSION: Since a decline of miR-181a concomitant with DUSP6 overexpression is the signature marker for age-associated T-cell senescence, these findings provide novel mechanistic insights into HCV-mediated premature T-cell aging through miR-181a-regulated DUSP6 signaling and reveal new targets for therapeutic rejuvenation of impaired T-cell responses during chronic viral infection.

KLRG1 impairs CD4+ T cell responses via p16ink4a and p27kip1 pathways: role in hepatitis B vaccine failure in individuals with hepatitis C virus infection.

Coinfection of hepatitis B virus (HBV) with hepatitis C virus (HCV) is quite common, leading to an increase in morbidity and mortality. As such, HBV vaccination is recommended in HCV-infected individuals. However, HBV vaccine responses in HCV-infected individuals are often blunted compared with uninfected populations. The mechanism for this failure of vaccine response in HCV-infected subjects remains unclear. In this study, we investigated the expression and function of an inhibitory receptor, killer cell lectin-like receptor subfamily G member 1 (KLRG1), in the regulation of CD4(+) T cells and HBV vaccine responses during HCV infection. We demonstrated that KLRG1 was overexpressed on CD4(+) T cells from HCV-infected, HBV vaccine nonresponders compared with HBV vaccine responders. The capacity of CD4(+) T cells to proliferate and secrete IL-2 cytokine was inversely associated with the level of KLRG1 expression. Importantly, blocking KLRG1 signaling resulted in a significant improvement in CD4(+) T cell proliferation and IL-2 production in HCV-infected, HBV vaccine nonresponders in response to TCR stimulation. Moreover, blockade of KLRG1 increased the phosphorylation of Akt (Ser(473)) and decreased the expression of cell cycle inhibitors p16(ink4a) and p27(kip1), which subsequently enhanced the expression of cyclin-dependent kinase 2 and cyclin E. These results suggest that the KLRG1 pathway impairs CD4(+) T cell responses to neoantigen and induces a state of immune senescence in individuals with HCV infection, raising the possibility that blocking this negative-signaling pathway might improve HBV vaccine responses in the setting of chronic viral infection.