An Insertion Within SIRPβ1 Shows a Dual Effect Over Alzheimer's Disease Cognitive Decline Altering the Microglial Response

Background

Microglial dysfunction plays a causative role in Alzheimer's disease (AD) pathogenesis. Here we focus on a germline insertion/deletion variant mapping SIRPβ1, a surface receptor that triggers amyloid-β(Aβ) phagocytosis via TYROBP.

Objective

To analyze the impact of this copy-number variant in SIRPβ1 expression and how it affects AD molecular etiology.

Methods

Copy-number variant proxy rs2209313 was evaluated in GERALD and GR@ACE longitudinal series. Hippocampal specimens of genotyped AD patients were also examined. SIRPβ1 isoform-specific phagocytosis assays were performed in HEK393T cells.

Results

The insertion alters the SIRPβ1 protein isoform landscape compromising its ability to bind oligomeric Aβ and its affinity for TYROBP. SIRPβ1 Dup/Dup patients with mild cognitive impairment show an increased cerebrospinal fluid t-Tau/Aβ ratio (p = 0.018) and a higher risk to develop AD (OR = 1.678, p = 0.018). MRIs showed that Dup/Dup patients exhibited a worse initial response to AD. At the moment of diagnosis, all patients showed equivalent Mini-Mental State Examination scores. However, AD patients with the duplication had less hippocampal degeneration (p < 0.001) and fewer white matter hyperintensities. In contrast, longitudinal studies indicate that patients bearing the duplication allele show a slower cognitive decline (p = 0.013). Transcriptional analysis also shows that the SIRPβ1 duplication allele correlates with higher TREM2 expression and an increased microglial activation.

Conclusions

The SIRPβ1 internal duplication has opposite effects over MCI-to-Dementia conversion risk and AD progression, affecting microglial response to Aβ. Given the pharmacological approaches focused on the TREM2-TYROBP axis, we believe that SIRPβ1 structural variant might be considered as a potential modulator of this causative pathway.

The female upper reproductive tract harbors endogenous microbial profiles

Introduction

The female reproductive tract harbours unique microbial communities (known as microbiota) which have been associated with reproductive functions in health and disease. While endometrial microbiome studies have shown that the uterus possesses higher bacterial diversity and richness compared to the vagina, the knowledge regarding the composition of the Fallopian tubes (FT) is lacking, especially in fertile women without any underlying conditions.

Methods

To address this gap, our study included 19 patients who underwent abdominal hysterectomy for benign uterine pathology, and 5 women who underwent tubal ligation as a permanent contraceptive method at Hospital Clínico Universitario Virgen de la Arrixaca (HCUVA). We analyzed the microbiome of samples collected from the FT and endometrium using 16S rRNA gene sequencing.

Results

Our findings revealed distinct microbiome profiles in the endometrial and FT samples, indicating that the upper reproductive tract harbors an endogenous microbiome. However, these two sites also shared some similarities, with 69% of the detected taxa Being common to both. Interestingly, we identified seventeen bacterial taxa exclusively present in the FT samples, including the genera Enhydrobacter, Granulicatella, Haemophilus, Rhizobium, Alistipes, and Paracoccus, among others. On the other hand, 10 bacterial taxa were only found in the endometrium, including the genera Klebsiella, Olsenella, Oscillibacter and Veillonella (FDR <0.05). Furthermore, our study highlighted the influence of the endometrial collection method on the findings. Samples obtained transcervically showed a dominance of the genus Lactobacillus, which may indicate potential vaginal contamination. In contrast, uterine samples obtained through hysterescopy revealed higher abundance of the genera Acinetobacter, Arthrobacter, Coprococcus, Methylobacterium, Prevotella, Roseburia, Staphylococcus, and Streptococcus.

Discussion

Although the upper reproductive tract appears to have a low microbial biomass, our results suggest that the endometrial and FT microbiome is unique to each individual. In fact, samples obtained from the same individual showed more microbial similarity between the endometrium and FT compared to samples from different women. Understanding the composition of the female upper reproductive microbiome provides valuable insights into the natural microenvironment where processes such as oocyte fertilization, embryo development and implantation occur. This knowledge can improve in vitro fertilization and embryo culture conditions for the treatment of infertility.

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele.

Genomic Characterization of Host Factors Related to SARS-CoV-2 Infection in People with Dementia and Control Populations: The GR@ACE/DEGESCO Study

Emerging studies have suggested several chromosomal regions as potential host genetic factors involved in the susceptibility to SARS-CoV-2 infection and disease outcome. We nested a COVID-19 genome-wide association study using the GR@ACE/DEGESCO study, searching for susceptibility factors associated with COVID-19 disease. To this end, we compared 221 COVID-19 confirmed cases with 17,035 individuals in whom the COVID-19 disease status was unknown. Then, we performed a meta-analysis with the publicly available data from the COVID-19 Host Genetics Initiative. Because the APOE locus has been suggested as a potential modifier of COVID-19 disease, we added sensitivity analyses stratifying by dementia status or by disease severity. We confirmed the existence of the 3p21.31 region (LZTFL1, SLC6A20) implicated in the susceptibility to SARS-CoV-2 infection and TYK2 gene might be involved in COVID-19 severity. Nevertheless, no statistically significant association was observed in the COVID-19 fatal outcome or in the stratified analyses (dementia-only and non-dementia strata) for the APOE locus not supporting its involvement in SARS-CoV-2 pathobiology or COVID-19 prognosis.

Common variants in Alzheimer's disease and risk stratification by polygenic risk scores

Genetic discoveries of Alzheimer's disease are the drivers of our understanding, and together with polygenetic risk stratification can contribute towards planning of feasible and efficient preventive and curative clinical trials. We first perform a large genetic association study by merging all available case-control datasets and by-proxy study results (discovery n = 409,435 and validation size n = 58,190). Here, we add six variants associated with Alzheimer's disease risk (near APP, CHRNE, PRKD3/NDUFAF7, PLCG2 and two exonic variants in the SHARPIN gene). Assessment of the polygenic risk score and stratifying by APOE reveal a 4 to 5.5 years difference in median age at onset of Alzheimer's disease patients in APOE ɛ4 carriers. Because of this study, the underlying mechanisms of APP can be studied to refine the amyloid cascade and the polygenic risk score provides a tool to select individuals at high risk of Alzheimer's disease.

First Report of Xylella fastidiosa in Nerium oleander in Costa Rica

Oleander (Nerium oleander L.) shrubs presenting mottling, leaf tip and margin scorch, short internodes, defoliation, and branch dieback were observed at different localities in the Central Valley in Costa Rica. Severity of the symptoms ranged widely, and most plants showed both diseased and healthy branches. In severe cases, entire sections of the plant were defoliated. Symptoms resembled those described for oleander leaf scorch (OLS) caused by the bacterium Xylella fastidiosa in the United States (3). This bacterium has been reported in coffee and citrus plants in Costa Rica. Sixty plants from five different places were sampled and tested using ELISA (Agdia Inc., Elkhart, IN) against X. fastidiosa. Thirty-five plants showed absorbance mean value of duplicate wells greater than the mean of control wells plus three times the standard deviation, and therefore were considered positive. Thirty-three of the sixty samples were processed for an immunofluorescence assay modified from Carbajal et al. (1) with antibody to X. fastidiosa (Agdia Inc.). Thirteen samples showed fluorescent rod-shaped bacilli with morphology similar to those observed from a pure culture of X. fastidiosa obtained from coffee. Ten of these thirteen samples were positive by ELISA. DNA extracts (2) from three of the oleander plants with high ELISA absorbance values were tested by nested PCR with primer pair 272-1/272-2 followed by the pair 272-1 int/272-2 int (4). Two of the samples were positive for the bacterium and one of the PCR products was cloned and sequenced in both directions (GenBank Accession No. EU009615). The negative (PCR mix) and positive (pure culture of X. fastidiosa isolated from grapevine) controls for nested-PCR were indeed negative and positive, respectively. The BLAST program was used to compare the sequence to the nucleotide collection (nr/nt) and Microbe Assembled Genomes databases in GenBank. All matches corresponded to X. fastidiosa sequences. The sequence showed 97% similarity with strains Found-4 (coffee strain from Brazil) and Found-5 (citrus strain from Brazil) and 96% similarity with strain Ann-1 from oleander in California. On the basis of serological, microscopic, and molecular detection of X. fastidiosa from oleander exhibiting symptoms of OLS similar to those reported in the literature, this pathogen likely is causing the symptoms we observed in Costa Rica. References: (1) D. Carbajal et al. Curr. Microbiol. 49:372, 2004. (2) M. J. Green et al. Plant Dis. 83:482, 1999. (3) Q. Huang et al. Plant Dis. 88:1049, 2004. (4) M. R. Pooler and J. S. Hartung. Curr. Microbiol. 31:377, 1995.

Liver transduction with a simian virus 40 vector encoding insulin-like growth factor I reduces hepatic damage and the development of liver cirrhosis

Liver transplantation is the only treatment for advanced liver cirrhosis. Therapies halting the progression of the disease are urgently needed. Administration of recombinant insulin-like growth factor-I (rIGF-I) induces hepatoprotective effects in experimental cirrhosis. Therefore, we analyzed the efficacy of a recombinant simian virus 40 vector (rSV40) encoding IGF-I (rSVIGF-I) to prevent cirrhosis progression. First, transgene expression was evaluated in mice injected with rSV40 encoding luciferase, which showed long-term hepatic expression of the transgene. Interestingly, luciferase expression increased significantly in CCl(4)-damaged livers and upon IGF-I administration, thus liver injury and IGF-I expression from rSVIGF-I should favor transgene expression. rSVIGF-I therapeutic efficacy was studied in rats where liver cirrhosis was induced by CCl(4) inhalation during 36 weeks. At the end of the study, the hepatic levels of IGF-I and IGF-binding protein 3 were higher in rSVIGF-I-treated rats than in control cirrhotic animals. Cirrhotic rats treated with rSVIGF-I had reduced serum bilirubin, transaminases and liver fibrosis scores and increased hepatic expression of hepatocyte growth factor and STAT3alpha as compared to cirrhotic animals. Furthermore, cirrhotic animals showed testis atrophy and altered spermatogenesis, whereas testicular size and histology were normal in cirrhotic rats that received rSVIGF-I. Therefore, rSV40-mediated sustained expression of IGF-I in the liver slowed cirrhosis progression.

First Report of Xylella fastidiosa Infecting Citrus in Costa Rica

Citrus variegated chlorosis (CVC) is an important disease mainly of sweet orange (Citrus sinensis (L.) Osbeck) cultivars. It was first described in Brazil in the state of Sā Paulo in 1987 (4). The disease has spread to all Brazilian states that grow citrus and is affecting more than one-third of the orange trees grown in Brazil. CVC is caused by Xylella fastidiousa, a xylem-limited, gram-negative bacterium. During the last 4 years, symptoms including leaf interveinal chlorosis, stunting, canopy dieback, and hard and undersized fruits, similar to those caused by CVC (3), appeared in sweet orange trees used as shade plants for coffee plantations and as fence posts in Costa Rica. Necrotic lesions on the abaxial side of the leaves as reported in Brazil were rarely observed. Leaf petiole samples from 25 symptomatic sweet orange trees reacted positively with a X fastidiosa-specific antiserum (AGDIA Inc., Elkart, IN) in a double-sandwich antibody enzyme-linked immunosorbent assay (DAS-ELISA). A fastidious, gram-negative bacterium identified as X. fastidiosa using DAS-ELISA was isolated on perwinkle wilt (PW) medium plates (1) from citrus stems showing CVC symptoms, but not from asymptomatic trees. The isolated colonies were circular and opalescent with diameters of 2 to 3 mm and were clearly visible within 6 to 7 days after streaking. Petiole sections from symptomatic plants observed with scanning electron microscopy showed rod-shaped bacteria with rippled cell walls tightly packed in xylem vessels, as described for X. fastidiosa previously (2), and with transmission electron microscopy, the bacteria were morphologically similar to those reported previously for CVC (2). To our knowledge, this is the first report of X. fastidiosa associated with citrus in Costa Rica. References: (1) M. J. Davis et al. Curr. Microbiol. 6:309, 1981. (2) J. S. Hartung et al. Phytopathology 84:591, 1994. (3) R. F. Lee et al. Summa Phytopathol. 19:123, 1993. (4) V. Rossetti et al. 1990, C.R. Acad. Sci. (Paris) 310:345-349.

First Report of Xylella fastidiosa Infecting Coffee in Costa Rica

In 1995, severe symptoms were observed on 'Caturra' and 'Catuaí' coffee (Coffea arabica L.) varieties in farms in the southern part of the Central Valley in Costa Rica. Symptoms were reduced leaf size, malformation of leaves, curling of leaf edges, shortening of internodes, and severe leaf chlorotic mosaic, which sometimes became necrotic. Abortion of flowers and young beans was also observed, with a reduction in yield. Plants also showed irregular growth with an atypical curling appearance that gave rise to the Spanish name "crespera." Ten and three healthy plants were inoculated by grafting in the greenhouse, using infected and healthy budwoods, respectively. Approximately 6 months after inoculation, 3 of 10 grafted plants with infected budwoods showed symptoms of leaf chlorosis, curling, and malformation of leaves and bunched new flushes. Samples of 39 symptomatic plants collected from the field and samples of 3 healthy plants maintained in the greenhouse were tested by enzyme-linked immunosorbent assay (ELISA). All (100%) analyzed symptomatic samples were positive for X. fastidiosa, and all healthy controls were negative. The symptoms observed in Costa Rica are different from those described for coffee leaf scorch in Brazil (1,2), but the climatological conditions and soil type present in Costa Rica are also very different from the areas where X. fastidiosa occurs in Brazil. Leafhoppers were collected randomly in one of the most affected regions. Graphocephala permagna and Erythrogonia sonora were the most frequent insect species found associated with coffee. In ELISA, 34.5% (10 of 29) and 23.8% (5 of 21) of the collected specimens belonging to G. permagna and E. sonora, respectively, tested positive for X. fastidiosa. These positive ELISAs do not necessarily mean that the insect is a vector. The results presented here extend the known geographic distribution of X. fastidiosa. To our knowledge, this is the first report of X. fastidiosa in coffee in Costa Rica. References: (1) M. J. G. Beretta et al. Plant Dis. 80:821, 1996. (2) de Lima et al. Plant Dis. 82:94, 1998.

Regulation of gene transcription in the epididymis

The epididymis exhibits region-specific as well as cell-specific patterns of gene expression within the epithelium. The spatial and temporal patterns of gene expression originate during development and are critical to the formation and maintenance of a fully functional epididymis. Despite the number of mechanisms reported to contribute to the regulation of eukaryotic gene expression, little is known about the specific mechanisms involved in the control of epididymal gene expression. This review will outline some of the cis-DNA elements and associated transcription factors that have been identified in the epididymis, in addition to discussing the potential role of co-regulator molecules and changes in chromatin structure as critical control points of gene expression. Although gene expression can be controlled at several points, discussion will focus on gene regulation at the transcriptional level. The role of post-transcriptional control, with particular attention to mRNA stability, will also be discussed.

Expression of the lipocalin-type prostaglandin D synthase gene in the reproductive tracts of Holstein bulls

The aim of this study was to localize expression of the prostaglandin D synthase gene in the reproductive tracts of Holstein bulls using northern blotting and in situ hybridization. For northern blotting, a digoxigenin-labelled prostaglandin D synthase cDNA probe was used to probe blots containing RNA isolated from the testes, epididymides, vas deferens, ampullae, seminal vesicles, prostate and bulbourethral glands of bulls. The digoxigenin-labelled cDNA for the bovine homologue of prostaglandin D synthase hybridized to a single band (approximately 0.9 kb) to RNA samples from the caput, corpus and cauda epididymides, as well as RNA samples from the vas deferens and the ampulla. The probe also detected a single band in testis samples, although the transcript size was slightly larger (approximately 1.0 kb) than the transcript found in the other tissues. The highest expression of prostaglandin D synthase was observed in the testes and caput epididymides. Prostaglandin D synthase transcripts were not found in the seminal vesicles or the prostate or bulbourethral glands using northern blotting. For in situ hybridization, antisense and sense riboprobes were synthesized and used to hybridize to cryosections obtained from the reproductive tissues of bulls. In situ hybridization of bull testes showed that prostaglandin D synthase transcripts were present within the germ cells in the adluminal compartment of the seminiferous tubules containing round and elongated spermatids, indicating that expression varied with stage of development of the seminiferous tubules. Prostaglandin D synthase expression was observed in the epithelial cells of the epididymides with greatest expression occurring in the caput epididymidis. Some expression was also observed in the epithelial cells of the vas deferens and a few cells of some lobules in the prostate and bulbourethral glands. Expression of the prostaglandin D synthase gene was not detected in ampullae or seminal vesicles by in situ hybridization.

Osteopontin gene expression in the Holstein bull reproductive tract

The objective of this study was to localize gene expression of osteopontin in the Holstein bull reproductive tract using Northern blot analysis and in situ hybridization. For Northern blot analysis, a digoxigenin-labeled osteopontin complementary deoxyribonucleic acid (cDNA) was used to probe blots containing total ribonucleic acid (RNA) isolated from the testis, epididymis, vas deferens, ampulla, seminal vesicle, prostate, and bulbourethral glands. The digoxigenin-labeled cDNA for the bovine homologue of osteopontin was hybridized to a single band at approximately 1.6 kb to RNA samples from the ampulla and seminal vesicle. For in situ hybridization studies, antisense and sense riboprobes were synthesized and used to hybridize cryosections that had been obtained from bull reproductive tissues. In situ hybridization of the bull testis detected osteopontin messenger RNA in the developing germ cells. Osteopontin gene expression was detected only in seminiferous tubules that contained elongated spermatids, which suggests that expression varies with the stage of the seminiferous epithelium. Within the epididymis, silver grains were distributed over the sperm that were located within the lumen of the caput, corpus, and cauda epididymis. Osteopontin expression was primarily observed in the epithelial cells of the ampulla. Antisense riboprobes also hybridized to sperm that were located within the lumen of the ampulla, confirming the presence of osteopontin transcripts in the haploid male gamete.