Special Issue Editorial: "Infections, Inflammation and Neurodegeneration in Alzheimer Disease" Infections, Neuronal Senescence, and Dementia.

Alzheimer's disease (AD) is a complex chronic disease of the brain characterized by several neurodegenerative mechanisms and is responsible for most dementia cases in the elderly. Declining immunity during ageing is often associated with peripheral chronic inflammation, and chronic neuroinflammation is a constant component of AD brain pathology. In the Special Issue published in 2021 eight papers were collected regarding different aspects of neurodegeneration associated with AD. Five papers presented and discussed infectious agents involved in brain AD pathology and three discussed data regarding receptors regulation and possible treatment of the disease. Below I will discuss and further elaborate on topics related to infections, inflammation, and neurodegenerative pathways in AD and brain senescence. The topic presented here may contribute to early intervention protocols for preventing or slowing the progression of cognitive deterioration in the elderly.

Activation of Endogenous Retrovirus, Brain Infections and Environmental Insults in Neurodegeneration and Alzheimer's Disease.

Chronic neurodegenerative diseases are complex, and their pathogenesis is uncertain. Alzheimer's disease (AD) is a neurodegenerative brain alteration that is responsible for most dementia cases in the elderly. AD etiology is still uncertain; however, chronic neuroinflammation is a constant component of brain pathology. Infections have been associated with several neurological diseases and viruses of the Herpes family appear to be a probable cause of AD neurodegenerative alterations. Several different factors may contribute to the AD clinical progression. Exogeneous viruses or other microbes and environmental pollutants may directly induce neurodegeneration by activating brain inflammation. In this paper, we suggest that exogeneous brain insults may also activate retrotransposons and silent human endogenous retroviruses (HERVs). The initial inflammation of small brain areas induced by virus infections or other brain insults may activate HERV dis-regulation that contributes to neurodegenerative mechanisms. Chronic HERV activation in turn may cause progressive neurodegeneration that thereafter merges in cognitive impairment and dementia in genetically susceptible people. Specific treatment for exogenous end endogenous pathogens and decreasing pollutant exposure may show beneficial effect in early intervention protocol to prevent the progression of cognitive deterioration in the elderly.

Impaired Innate Immunity Mechanisms in the Brain of Alzheimer's Disease.

Among environmental factors likely associated with Alzheimer's disease (AD), persistent virus infections, and age-related progressive decline of immune competence might play a pivotal role. However, AD antimicrobial brain immune responses are poorly investigated. The present study focused on genes involved in antimicrobial defenses, especially against virus infections, in the AD brain. In particular, mRNA levels of IRF7, MED23, IL28B, and IFN-α genes were analyzed in hippocampus and temporal cortex brain samples from AD and non-demented controls. All subjects were also genotyped for APOE ε, IRF7, MED23, and IL28B gene polymorphisms. Most AD patients showed decreased mRNA levels of all investigated genes in the hippocampus and temporal cortex. However, a small group of AD patients showed increased hippocampal mRNA expression of MED23, IL28B, and IFN-α. mRNA levels of MED23, IL28B, IFN-α from the hippocampus and those of MED23 from the temporal cortex were further decreased in APOE ε4 allele AD carriers. Moreover, rs6598008 polymorphism of IRF7 was significantly associated with decreased hippocampal expression of IRF7, MED23, IL28B, and IFN-α. These findings suggest that AD brains show impaired innate antimicrobial gene expression profiles, and individual genetic makeup, such as positivity for the APOE ε4 and IRF7 A alleles, might affect brain immune efficiency.

Peripheral Inflammatory Markers and Antioxidant Response during the Post-Acute and Chronic Phase after Severe Traumatic Brain Injury.

Traumatic brain injury (TBI) is a mechanical insult to the brain caused by external forces and associated with inflammation and oxidative stress. The patients may show different profiles of neurological recovery and a combination of oxidative damage and inflammatory processes can affect their courses. It is known that an overexpression of cytokines can be seen in peripheral blood in the early hours/days after the injury, but little is known about the weeks and months encompassing the post-acute and chronic phases. In addition, no information is available about the antioxidant responses mediated by the major enzymes that regulate reactive oxygen species levels: superoxide dismutase, catalase, peroxidases, and GSH-related enzymes. This study investigates the 6-month trends of inflammatory markers and antioxidant responses in 22 severe TBI patients with prolonged disorders of consciousness, consecutively recruited in a dedicated neurorehabilitation facility. Patients with a high degree of neurological impairment often show an uncertain outcome. In addition, the profiles of plasma activities were related to the neurological recovery after 12 months. Venous peripheral blood samples were taken blindly as soon as clinical signs and laboratory markers confirmed the absence of infections, 3 and 6 months later. The clinical and neuropsychological assessment continued up to 12 months. Nineteen patients completed the follow-up. In the chronic phase, persistent high plasma levels of cytokines can interfere with cognitive functioning and higher post-acute levels of cytokines [interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL1b, IL6] are associated with poorer cognitive recoveries 12 months later. Moreover, higher IFN-γ, higher TNF-α, and lower glutathione peroxidase activity are associated with greater disability. The results add evidence of persistent inflammatory response, provide information about long-term imbalance of antioxidant activity, and suggest that the over-production of cytokines and the alteration of the redox homeostasis in the post-acute phase might adversely affect the neurological and functional recovery. Inflammatory and antioxidant activity markers might offer a feasible way to highlight some of the processes opposing recovery after a severe TBI.

Persistent infections, immune-senescence and Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia. Classical hallmarks of AD such as amyloid deposition and neurofibrillary tangles do not completely explain AD pathogenesis. Recent investigations proposed Aß peptide as an anti-microbial factor. Our previous works suggested that the concomitant presence of single nucleotide polymorphisms (SNPs) from AD genetic studies might impair antiviral defenses and increase the individual susceptibility to herpes virus infection. Viruses of herpes family by inducing frequent cycles of reactivation and latency constantly challenge the immune response and drive the accumulation of memory T cells. However, the immune system is not able to completely eradicate these viruses. The continuous antigen stimulation activates chronic inflammatory responses that may progressively induce neurodegenerative mechanisms in genetically susceptible elderly. The aim of this paper is to suggest new perspectives in clinical pathogenesis of AD with potential prevention and new medical treatment of the age associated cognitive decline.

Peripheral leukocyte expression of the potential biomarker proteins Bdnf, Sirt1, and Psen1 is not regulated by promoter methylation in Alzheimer's disease patients.

The identification of Alzheimer's disease (AD) biomarkers is crucial to support drug discovery. Within putative biomarkers, peripheral Bdnf levels correlate with cognitive decline and AD, although conflicting findings are reported. Sirtuin 1 (Sirt1) serum levels are lower in AD patients and Presenilin 1 (Psen1) is expressed by blood cells. DNA methylation is altered in AD patients, suggesting that epigenetic mechanisms play a role in AD pathophysiology. The objective of this study was to investigate promoter methylation levels of potential biomarkers in AD cases and controls. Peripheral blood DNA methylation levels were analysed by methylation-specific primer real-time PCR. Bdnf promoter methylation levels did not differ between AD patients and controls. Similarly, Sirt1 promoter revealed minimal levels of methylation which did not display significant differences between groups. No significant difference was revealed between AD patients and controls also in Psen1 methylation, showing a large variability of values among subjects. Although peripheral Bdnf expression is associated with differential promoter methylation in psychiatric and neurological disorders, our results suggest that different mechanisms take place in AD. The finding that the control of Sirt1 protein levels in blood is not exerted through the repression of mRNA expression by promoter hypermethylation is in agreement with previous data. In contrast, other studies reported that Psen1 methylation may be increased or decreased in AD patients, suggesting that additional studies are required. In conclusion, this study shows that peripheral levels of the potential AD biomarker proteins Bdnf, Sirt1, and Psen1 are not regulated by different promoter methylation.

Variants in Antiviral Genes are Risk Factors for Cognitive Decline and Dementia.

A gene association study of factors regulating antiviral response such as interferon (IFN)-λ3, also known as IL-28B, mediator complex (Med) 23, and interferon regulatory factor (IRF) 7 with cognitive deterioration and Alzheimer's disease (AD) was performed. Differences in the TT genotype distribution of IL-28B single nucleotide polymorphism (SNP) between AD patients and controls were found. The GG genotype of Med23 gene appeared to influence the progression of the disease, being more frequent in the APOE ɛ4 negative elderly that developed AD during the five year follow-up. Leukocyte positivity for Epstein Barr virus (EBV) and human herpes virus (HHV)-6 DNA was analyzed. Med23 GG genotype correlated with the positivity to HHV-6 DNA. EBV and HHV-6 plasma IgG levels were also investigated and EBV IgG levels were increased in AD with the IRF7 GG genotype. A differential genetic background in genes regulating anti-virus responses was associated with an increased risk of cognitive decline and AD. EBV and HHV-6 appeared to be risk factors for AD in genetically susceptible elderly.

The 21st century epidemic: infections as inductors of neuro-degeneration associated with Alzheimer's Disease.

Alzheimer's disease (AD) is a complex disease resulting in neurodegeneration and cognitive impairment. Investigations on environmental factors implicated in AD are scarce and the etiology of the disease remains up to now obscure. The disease's pathogenesis may be multi-factorial and different etiological factors may converge during aging and induce an activation of brain microglia and macrophages. This microglia priming will result in chronic neuro-inflammation under chronic antigen activation. Infective agents may prime and drive iper-activation of microglia and be partially responsible of the induction of brain inflammation and decline of cognitive performances. Age-associated immune dis-functions induced by chronic sub-clinical infections appear to substantially contribute to the appearance of neuro-inflammation in the elderly. Individual predisposition to less efficient immune responses is another relevant factor contributing to impaired regulation of inflammatory responses and accelerated cognitive decline. Life-long virus infection may play a pivotal role in activating peripheral and central inflammatory responses and in turn contributing to increased cognitive impairment in preclinical and clinical AD.

SHIP2: a "new" insulin pathway target for aging research.

Strong evidence suggests that systemic inflammation and central adiposity contribute to and perpetuate metabolic syndrome. All of these alterations predispose individuals to type 2 diabetes mellitus (T2DM), cardiovascular disease, as well as Alzheimer's disease (AD), all characterized by chronic inflammatory status. On the other hand, extensive abnormalities in insulin and insulin-like growth factor I (IGF-I) and IGF-II signaling mechanisms in brains with AD have been demonstrated, suggesting that AD could be a third form of diabetes. The Src homology domain-containing inositol 5-phosphatase 2 (SHIP2) has an important role in the insulin pathway because its over-expression causes impairment of insulin/IGF-1 signaling. Because some single-nucleotide polymorphisms (SNP) of the gene encoding SHIP2 were significantly associated in T2DM patients with metabolic syndrome and some related conditions, we decided to conduct a case-control study on this gene, analyzing AD and T2DM subjects as cases and young, old, and centenarians as controls. Our results suggest a putative correlation between the the rs144989913 SNP and aging, both successful and unsuccessful, rather than age-related diseases. Because this SNP is an insertion/deletion of 28 bp, it might cause an alteration in SHIP2 expression. It is noteworthy that SHIP2 has been demonstrated to be a potent negative regulator of insulin signaling and insulin sensitivity. Many studies demonstrated the association of the insulin/IGF1 pathway with aging and longevity, so it is tempting to speculate that the found association with SHIP2 and aging might depend on its effect on the insulin/IGF-1 pathway.

Herpes virus in Alzheimer's disease: relation to progression of the disease.

Studies regarding different viruses of the herpes family, such as cytomegalovirus (CMV), Epstein-Barr virus (EBV), or human herpes virus 6 (HHV-6) in Alzheimer's disease (AD) are scarce. DNA from peripheral blood leukocytes (PBL) and brain samples were analyzed for the presence of CMV, EBV, or HHV-6. All samples were negative for CMV. EBV positivity was 6% in AD brains, whereas 45% of PBL samples from AD patients and 31% from controls were positive for EBV (p = 0.05). HHV-6 showed a 23% positivity in PBL samples from AD and 4% from controls (p = 0.002). 17% of AD brains were HHV-6 positive. Within a group of elderly individuals, followed up for 5 years, EBV-positive or HHV-6-positive PBL increased in those who developed clinical AD. Virus serological positivity was also investigated, and IgG levels for CMV and EBV antigens were also increased in those subjects who developed AD during the follow-up. Our findings suggest that EBV and HHV-6 may be environmental risk factors for cognitive deterioration and progression to AD in elderly persons.

Variations in inflammatory genes are associated with periodontitis.

BACKGROUND: Periodontitis is a multi-factorial disease and several risk-factors such as infections, inflammatory responses, oral hygiene, smoke, aging and individual predisposition are involved in the disease. Pathogens trigger chronic inflammation with cytokines release which in turn leads to the destruction of the connective and the teeth supporting bone. The identification of genetic factors controlling oral inflammation may increase our understanding of genetic predisposition to periodontitis.Single nucleotide polymorphisms in the promoter region of Vascular Endothelial Growth Factor, Alpha-1-Antichymotripsin, hydroxy-methyl-glutaryl CoA reductase, Interferon alpha, Interleukin-1 Beta, Interleukin 10, Interleukin 6 and Tumor Necrosis Factor- alpha genes from a case/control study were investigated. RESULTS: The C allele of Vascular Endothelial Growth Factor, A allele of Interleukin 10 and GG genotype of Tumor Necrosis Factor-α were individually associated with chronic periodontitis. However, the concomitant presence of the three genetic markers in the same subjects appeared to play a synergistic role and increased several folds the risk of the disease. CONCLUSIONS: Our findings offer new tools to implement the screening of unaffected subjects with an increased susceptibility of periodontitis and increase our understanding regarding the genetic inflammatory background related to familiarity of the disease.

Monocyte chemoattractant protein-1 promoter polymorphism and plasma levels in alzheimer's disease.

BACKGROUND: Neurodegenerative disorders such Alzheimer's disease (AD) are often characterized by senile plaques and neurofibrillary tangle. In addition, reactive astrogliosis, microglia activation and a chronic inflammation are found in AD brain. Activated microglia has been reported to express a large number of beta chemokines including monocyte chemoattractant protein-1 (MCP-1). The potential role of MCP-1 in AD pathogenesis is supported by the over expression of MCP-1 associated with an increase of amyloid deposition in transgenic mice. MCP-1 protein may be regulated by a single nucleotide polymorphism (SNP) occurring at position -2518 of the MCP-1 gene promoter. In this paper we correlated the A-2518G MCP-1 SNP distribution in three different populations: AD, control and MCI (mild cognitive impairment) population to evaluate whether this SNP might be a risk factor for AD or for MCI-AD conversion. MCP-1 plasma levels were also measured and correlated to the cognitive impairment (CIND) and AD risk. RESULTS: No differences in genotype distribution and allele frequencies of A-2518G MCP-1 SNP among AD patients, MCI subjects and controls were observed even after APOEe4 variation adjustment with logistic regression. However in MCI subjects, followed up for two years, this SNP appears to influence the progression of the disease; being the G allele slightly more frequent in MCI patients that developed AD. MCP-1 plasma levels were different among CIND (cognitive impairment but no dementia), AD and controls. The MCP-1 A-2518G promoter polymorphism did not affect MCP-1 plasma levels within the three populations. CONCLUSIONS: MCP-1 G allele did not affect the risk of AD, but slightly influenced MCI conversion to AD and MCP-1 plasma levels were increased in subjects with preclinical AD.

Haplotype of single nucleotide polymorphisms in exon 6 of the MZF-1 gene and Alzheimer's disease.

Our previous works showed that single nucleotide polymorphisms (SNPs) in genes with regulatory function upon inflammatory response and cholesterol metabolism were associated with Alzheimer's disease (AD) risk. The list comprises SNPs located on the promoters of alpha 1 antichymotrypsin (rs1884082), hydroxy methyl glutaryl coenzime A reductase (rs376140), tumor necrosis factor alpha (rs1800629), and interleukin 10 (rs1800869). Here we investigated the effect of these SNPs on the binding for transcription factors. We computationally detected putative binding sites for transcription factors located in the SNP regions. To this aim, the TESS program for scanning the promoter sequences against the binding-site models available at TRANSFACT and JASPAR databases was adopted. All the analyzed SNPs appeared to affect the binding of myeloid zinc finger protein 1 (MZF-1) to the promoter sequence of the above reported genes. Therefore 16 SNPs in MZF-1 gene were tested in 120 AD cases and 88 controls to asses a possible association between MZF-1 and AD. 14 SNPs showed no variability in AD and control populations, while two SNPs rs4756 and rs2228162 showed the three genotypes. Genotype distributions and allele frequencies of these two SNPs were comparable between AD and controls. On the other hand, the haplotype distribution of rs4756 and rs2228162 was different between AD and controls; being the AG haplotype associated with a decreased AD risk. In conclusion, selected SNPs in MZF-1 gene exert a minor effect on AD risk.

Pro-inflammatory genetic profile and familiarity of acute myocardial infarction.

BACKGROUND: Acute myocardial infarction (AMI) is a multifactorial disease with a complex pathogenesis where lifestyle, individual genetic background and environmental risk factors are involved. Altered inflammatory responses are implicated in the pathogenesis of atherosclerosis and a premature AMI of parents is associated with an increased risk of the disease in their offspring (Offs). However, the genetic background of familiarity for AMI is still largely unknown. To understand which genes may predispose to increased risk of cardiovascular disease gene polymorphism of immune regulatory genes, and clinical events from the Offs of parents with an early AMI were investigated. Genetics data from Offs were compared with those obtained from healthy subjects and an independent cohort of patients with clinical sporadic AMI. Rates of clinical events during a 24 years follow up from Offs and from an independent Italian population survey were also evaluated. RESULTS: This study showed that a genetic signature consisting of the concomitant presence of the CC genotype of VEGF, the A allele of IL-10 and the A allele of IFN-γ was indeed present in the Offs population. In fact, the above genetic markers were more frequent in unaffected Offs (46.4%) and patients with sporadic AMI (31.8%) than in the CTR (17.3%) and the differences were highly statistically significant (Offs vs CTR: p = 0.0001, OR = 4.129; AMI vs CTR: p = 0.0001, OR = 2.224). During the 24-year follow-up, Offs with a positive familiarity in spite of a relatively young age showed an increased prevalence of diabetes, ischemic heart disease and stroke. These findings reinforce the notion that subjects with a familial history of AMI are at risk of an accelerated aging of cardiovascular system resulting in cardiovascular events. CONCLUSION: Our data suggest that selected genes with immune regulatory functions are part of the complex genetic background contributing to familiarity for cardiovascular diseases. This inflammatory genetic profile, along with classical cardiovascular risk factors, may be used for better defining individual risk of AMI in unaffected subjects.

Gene signature in Alzheimer's disease and environmental factors: the virus chronicle.

Genome wide association investigations from large cohorts of patients with Alzheimer's disease (AD) and non demented controls (CTR) showed that a limited set of genes were associated (p > 10-5) with the disease. A very recent study from our group showed that an additional limited group of SNP in selected genes were associated with AD. In this report we argue that the association of these genes with AD is suggestive of a pivotal role of environmental factors in the pathogenesis of the disease and one of these factors is virus infection. In other words, the genetic signature revealed by genome wide association (GWA) studies discloses a network of genes that might influence the ability of the central nervous system to cope with and fight against the invasion by virus of the herpes family. In fact, Nectin-2 (NC-2); apolipoprotein E (APOE); glycoprotein carcinoembryonic antigen related cell adhesion molecule-16 (CEACAM-16); B-cell lymphoma-3 (Bcl-3); translocase of outer mitochondrial membrane 40 homolog (T0MM-40); complement receptor-1 (CR-l); APOJ or clusterin and C-type lectin domain A family-16 member (CLEC-16A); Phosphatidyl inositol- binding clathrin assembly protein gene (PICALM); ATP-bonding cassette, sub family A, member 7 (ABCA7); membrane spanning A4 (MSA4); CD2 associated protein (CD2AP); cluster of differentiation 33 (CD33); and ephrin receptor A1 (EPHA1) result in a genetic signature that might affect individual brain susceptibility to infection by the herpes virus family during aging, leading to neuronal loss, inflammation, and amyloid deposition.

Analysis of polymorphisms Leiden Factor V G1691A and prothrombin G20210A as risk factors for acute myocardial infarction.

Thrombotic risk increases in elderly, therefore, the understanding of the genetic predisposition of hypercoagulability could make the difference in the prevention of venous and/or arterial thrombotic events. Laboratory evaluation of hyperfibrinogenemia, increased Factor VII levels, antiphospholipid antibodies presence and hyperhomocysteinemia are considered to have a consistent high predictivity for arterial thrombophilic diseases. Anyway, a large debate exists on the validity of testing Leiden Factor V (FV) G1691A and/or prothrombin (FII) G20210A polymorphisms in patients affected by arterial thrombotic diseases, despite of the several observations described. Here we report data strongly suggesting that at least the FII G20210A polymorphism might be considered an important risk factor for acute myocardial infarction in aged patients (55-80 years old). On the other hand, in spite of a not different genotypic and allelic distribution for the Leiden FV G1691A mutation, the presence of one or both the two polymorphisms is significantly higher among cases than in controls. In conclusion, our data suggest that FII G20210A and/or Leiden FV might be involved as risk factor for arterial disorders in about 5% of old subjects, justifying the opportunity of a genetic screening and an eventual preventive treatment, in particular in old subjects in which other and major risk factors, as hypertension and atherosclerosis, are detected.

Reduced plasma levels of P-selectin and L-selectin in a pilot study from Alzheimer disease: relationship with neuro-degeneration.

Neurodegenerative processes associated with Alzheimer's disease (AD) are accompanied by reactive astrogliosis and microglia activation and a role for chronic inflammation in the brain degeneration of these patients has been suggested. Moreover impaired immune functions in AD brains might also influence the disease's progression. Therefore, it is of interest to further characterized inflammatory molecules in the peripheral blood of patients with AD and its relationship with cognitive decline. A complex picture emerged in this pilot study and IL-8, IFN-gamma, MCP-1 and VEGF levels were increased in AD. Levels of P-selectin and L-selectin were decreased in AD and lowest in AD patients with highest cognitive decline. Our findings suggest that these molecules may induce alterations of endothelial regulation and influence neurodegenerative processes of AD.

Role of prothrombotic polymorphisms in successful or unsuccessful aging.

The study of the genetic profile of centenarians aims to identify the genes and allelic variants which may influence a greater life expectancy and that can be considered as predisposing factors associated to the aging diseases, such as Alzheimer. Centenarians, that represent a cohort of selected survivors, show an hypercoagulability state characterised by striking signs of high coagulation enzyme activity, as directly assessed by the tested higher plasma level of some important factors involved in the haemostasis balance. Anyway, these individuals seem to have a reduced susceptibility to dementia, as well as to cardiovascular events. In this study we analyze the frequencies of Leiden Factor V polymorphism (G1691A), and G20210A of prothrombin (FII) in three cohorts of subjects: patients with Alzheimer's disease (unsuccessful aging), nonagenarians (successful aging) and young healthy controls, to assess whether allelic variants associated to the modification of haemostatic system function, may play a role in the protection or susceptibility to Alzheimer disease, as well as to reach a successful aging. No significant differences were observed in the frequencies of the three groups studied. These results indicate that the presence or absence of the gene variants examined did not influence the achievement of advanced age and are not risk factors for Alzheimer's disease. The state of hypercoagulability and the possession of these risk alleles appear to be compatible with the achievement of longevity and are not implied as risk factors in Alzheimer disease development.

Evidence of the association of BIN1 and PICALM with the AD risk in contrasting European populations.

Recent genome-wide association studies have identified 5 loci (BIN1, CLU, CR1, EXOC3L2, and PICALM) as genetic determinants of Alzheimer's disease (AD). We attempted to confirm the association between these genes and the AD risk in 3 contrasting European populations (from Finland, Italy, and Spain). Because CLU and CR1 had already been analyzed in these populations, we restricted our investigation to BIN1, EXO2CL3, and PICALM. In a total of 2816 AD cases and 2706 controls, we unambiguously replicated the association of rs744373 (for BIN1) and rs541458 (for PICALM) polymorphisms with the AD risk (odds ratio [OR] = 1.26, 95% confidence interval [CI] [1.15-1.38], p = 2.9 × 10(-7), and OR = 0.80, 95% CI [0.74-0.88], p = 4.6 × 10(-7), respectively). In a meta-analysis, rs597668 (EXOC3L2) was also associated with the AD risk, albeit to a lesser extent (OR = 1.19, 95% CI [1.06-1.32], p = 2.0 × 10(-3)). However, this signal did not appear to be independent of APOE. In conclusion, we confirmed that BIN1 and PICALM are genetic determinants of AD, whereas the potential involvement of EXOC3L2 requires further investigation.