Meox2 haploinsufficiency increases neuronal cell loss in a mouse model of Alzheimer\u27s disease

Evidence suggests that multiple genetic and environmental factors conspire together to increase susceptibility to Alzheimer\u27s disease (AD). The amyloid cascade hypothesis states that deposition of the amyloid-β (Aβ) peptide is central to AD; however, evidence in humans and animals suggests that Aβ buildup alone is not sufficient to cause neuronal cell loss and cognitive decline. Mouse models that express high levels of mutant forms of amyloid precursor protein and/or cleaving enzymes deposit amyloid but do not show neuron loss. Therefore, a double-hit hypothesis for AD has been proposed whereby vascular dysfunction precedes and promotes Aβ toxicity. In support of this, copy number variations in mesenchyme homeobox 2 (MEOX2), a gene involved in vascular development, are associated with severe forms of AD. However, the role of MEOX2 in AD has not been studied. Here, we tested Meox2 haploinsufficiency in B6.APP/PS1 (B6.APBTg) mice, a mouse model of AD. Despite no overt differences in plaque deposition or glial activation, B6.APBTg mice that carry only one copy of Meox2 (B6.APBTg.Mx−/+) show increased neuronal cell loss, particularly in regions containing plaques, compared with B6.APBTgmice. Neuronal cell loss corresponds with a significant decrease in plaque-associated microvessels, further supporting a synergistic effect of vascular compromise and amyloid deposition on neuronal cell dysfunction in AD

Meox2 haploinsufficiency increases neuronal cell loss in a mouse model of Alzheimer\u27s disease

Evidence suggests that multiple genetic and environmental factors conspire together to increase susceptibility to Alzheimer\u27s disease (AD). The amyloid cascade hypothesis states that deposition of the amyloid-β (Aβ) peptide is central to AD; however, evidence in humans and animals suggests that Aβ buildup alone is not sufficient to cause neuronal cell loss and cognitive decline. Mouse models that express high levels of mutant forms of amyloid precursor protein and/or cleaving enzymes deposit amyloid but do not show neuron loss. Therefore, a double-hit hypothesis for AD has been proposed whereby vascular dysfunction precedes and promotes Aβ toxicity. In support of this, copy number variations in mesenchyme homeobox 2 (MEOX2), a gene involved in vascular development, are associated with severe forms of AD. However, the role of MEOX2 in AD has not been studied. Here, we tested Meox2 haploinsufficiency in B6.APP/PS1 (B6.APBTg) mice, a mouse model of AD. Despite no overt differences in plaque deposition or glial activation, B6.APBTg mice that carry only one copy of Meox2 (B6.APBTg.Mx−/+) show increased neuronal cell loss, particularly in regions containing plaques, compared with B6.APBTgmice. Neuronal cell loss corresponds with a significant decrease in plaque-associated microvessels, further supporting a synergistic effect of vascular compromise and amyloid deposition on neuronal cell dysfunction in AD

Intracellular bacillary burden reflects a burst size for Mycobacterium tuberculosis in vivo

We previously reported that Mycobacterium tuberculosis triggers macrophage necrosis in vitro at a threshold intracellular load of ~25 bacilli. This suggests a model for tuberculosis where bacilli invading lung macrophages at low multiplicity of infection proliferate to burst size and spread to naïve phagocytes for repeated cycles of replication and cytolysis. The current study evaluated that model in vivo, an environment significantly more complex than in vitro culture. In the lungs of mice infected with M. tuberculosis by aerosol we observed three distinct mononuclear leukocyte populations (CD11b(-) CD11c(+/hi), CD11b(+/lo) CD11c(lo/-), CD11b(+/hi) CD11c(+/hi)) and neutrophils hosting bacilli. Four weeks after aerosol challenge, CD11b(+/hi) CD11c(+/hi) mononuclear cells and neutrophils were the predominant hosts for M. tuberculosis while CD11b(+/lo) CD11c(lo/-) cells assumed that role by ten weeks. Alveolar macrophages (CD11b(-) CD11c(+/hi)) were a minority infected cell type at both time points. The burst size model predicts that individual lung phagocytes would harbor a range of bacillary loads with most containing few bacilli, a smaller proportion containing many bacilli, and few or none exceeding a burst size load. Bacterial load per cell was enumerated in lung monocytic cells and neutrophils at time points after aerosol challenge of wild type and interferon-γ null mice. The resulting data fulfilled those predictions, suggesting a median in vivo burst size in the range of 20 to 40 bacilli for monocytic cells. Most heavily burdened monocytic cells were nonviable, with morphological features similar to those observed after high multiplicity challenge in vitro: nuclear condensation without fragmentation and disintegration of cell membranes without apoptotic vesicle formation. Neutrophils had a narrow range and lower peak bacillary burden than monocytic cells and some exhibited cell death with release of extracellular neutrophil traps. Our studies suggest that burst size cytolysis is a major cause of infection-induced mononuclear cell death in tuberculosis

The Genome of a Pathogenic Rhodococcus: Cooptive Virulence Underpinned by Key Gene Acquisitions

We report the genome of the facultative intracellular parasite Rhodococcus equi, the only animal pathogen within the biotechnologically important actinobacterial genus Rhodococcus. The 5.0-Mb R. equi 103S genome is significantly smaller than those of environmental rhodococci. This is due to genome expansion in nonpathogenic species, via a linear gain of paralogous genes and an accelerated genetic flux, rather than reductive evolution in R. equi. The 103S genome lacks the extensive catabolic and secondary metabolic complement of environmental rhodococci, and it displays unique adaptations for host colonization and competition in the short-chain fatty acid–rich intestine and manure of herbivores—two main R. equi reservoirs. Except for a few horizontally acquired (HGT) pathogenicity loci, including a cytoadhesive pilus determinant (rpl) and the virulence plasmid vap pathogenicity island (PAI) required for intramacrophage survival, most of the potential virulence-associated genes identified in R. equi are conserved in environmental rhodococci or have homologs in nonpathogenic Actinobacteria. This suggests a mechanism of virulence evolution based on the cooption of existing core actinobacterial traits, triggered by key host niche–adaptive HGT events. We tested this hypothesis by investigating R. equi virulence plasmid-chromosome crosstalk, by global transcription profiling and expression network analysis. Two chromosomal genes conserved in environmental rhodococci, encoding putative chorismate mutase and anthranilate synthase enzymes involved in aromatic amino acid biosynthesis, were strongly coregulated with vap PAI virulence genes and required for optimal proliferation in macrophages. The regulatory integration of chromosomal metabolic genes under the control of the HGT–acquired plasmid PAI is thus an important element in the cooptive virulence of R. equi

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

APOE Stabilization by Exercise Prevents Aging Neurovascular Dysfunction and Complement Induction.

Aging is the major risk factor for neurodegenerative diseases such as Alzheimer\u27s disease, but little is known about the processes that lead to age-related decline of brain structures and function. Here we use RNA-seq in combination with high resolution histological analyses to show that aging leads to a significant deterioration of neurovascular structures including basement membrane reduction, pericyte loss, and astrocyte dysfunction. Neurovascular decline was sufficient to cause vascular leakage and correlated strongly with an increase in neuroinflammation including up-regulation of complement component C1QA in microglia/monocytes. Importantly, long-term aerobic exercise from midlife to old age prevented this age-related neurovascular decline, reduced C1QA+ microglia/monocytes, and increased synaptic plasticity and overall behavioral capabilities of aged mice. Concomitant with age-related neurovascular decline and complement activation, astrocytic Apoe dramatically decreased in aged mice, a decrease that was prevented by exercise. Given the role of APOE in maintaining the neurovascular unit and as an anti-inflammatory molecule, this suggests a possible link between astrocytic Apoe, age-related neurovascular dysfunction and microglia/monocyte activation. To test this, Apoe-deficient mice were exercised from midlife to old age and in contrast to wild-type (Apoe-sufficient) mice, exercise had little to no effect on age-related neurovascular decline or microglia/monocyte activation in the absence of APOE. Collectively, our data shows that neurovascular structures decline with age, a process that we propose to be intimately linked to complement activation in microglia/monocytes. Exercise prevents these changes, but not in the absence of APOE, opening up new avenues for understanding the complex interactions between neurovascular and neuroinflammatory responses in aging and neurodegenerative diseases such as Alzheimer\u27s disease. PLoS Biol 2015 Oct 29; 13(10):e1002279

Distribution of Mtb infection within monocytic cell populations in the lung.

<p>Whole lung leukocytes were harvested from groups of mice with TB (4 and 10 weeks p.i.) and compared to uninfected controls. Monocytic cells were sorted into AM, RM and mDC as described in <i>Materials and Methods</i>. Ziehl-Neelsen staining was performed on cytospin preparations of sorted populations. (A) The proportion of AM, RM and mDC within the total lung monocytic cell population of uninfected mice and mice with pulmonary TB. (B) The proportion of AM, RM and mDC containing any AFB in mice with pulmonary TB. (C) The proportion of GFP-labeled lung leukocytes, GFP⁺ AM, RM and mDC, in uninfected mice and mice with TB. Lung leukocytes within the airspace were transduced by tracheal instillation of WT mice with CMV-GFP-W. After 8 weeks, one group of GFP-transduced mice was challenged by aerosol with 300 CFU of Mtb Erdman delivered to the lung. The category <i>Other</i> comprised cells that could not be categorized as AM, RM or mDC based on light scatter characteristics and CD11b/CD11c staining. By light microscopy, cells in the <i>Other</i> category included a small number of neutrophils that may have acquired GFP by efferocytosis, as well of cells with monocytic appearance that had very high intracellular Mtb burden and features of cell death. Monocytic cell subsets were classified by surface immunostaining as alveolar macrophages (AM; CD11b⁻ CD11c^+/hi), recruited monocyte/macrophages (RM; CD11b^+/lo CD11c^lo/−) and myeloid dendritic cells (mDC; CD11b^+/hi CD11c^+/hi).</p

Distribution of AFB loads in lung monocytic cells and neutrophils from WT and GKO mice with TB.

<p>GKO and WT mice were challenged by aerosol with 100 CFU of Mtb Erdman delivered to the lung. BAL was performed 7, 11, 14, 18 and 21 days p.i. A total of 4.8×10⁶ Ziehl-Neelsen stained cells were counted. Numbers of AFB per cell were grouped into 5 bins as indicated and counted separately in monocytic cells (A) and neutrophils (B) from GKO and WT mice. Results are presented as mean log₁₀ AFB⁺ cells in each bin ± SD. GKO mice had a greater number of AFB⁺ monocytic cells in all bins at 7 days p.i. and a significantly higher proportion of cells with ≥11 AFB compared to WT mice at that time point. The proportion of cells within each bin was similar between WT and GKO mice on days 11–18 p.i. but by day 21 p.i. the proportion of cells with ≥11 AFB fell significantly in WT compared to GKO mice. On day 21 p.i. the number of AFB⁺ neutrophils from GKO mice was significantly higher than earlier time points. In contrast, the number of AFB⁺ neutrophils from WT mice was significantly lower on day 21 than day 18 p.i.</p

Enumeration of intracellular Mtb in lung phagocytes.

<p>BAL cells and whole lung leukocytes were isolated from C57BL/6 mice 2 weeks after aerosol challenge with Mtb Erdman. Ziehl-Neelsen stained cytospin preparations were used to visualize and count intracellular AFB by light microscopy. Representative photomicrographs show examples of infected cells along with AFB counts as indicated (magnification, 400×).</p

Kinetics of intracellular Mtb growth in vivo.

<p>BAL cells and whole lung leukocytes were harvested at 1, 2, 3 and 8 weeks after aerosol infection of mice with 300 CFU Mtb Erdman delivered to the lung. Cells from both sources were counted and cytospin preparations were made for Ziehl-Neelsen staining. (A) The total number of Mtb-infected (AFB⁺) cells was derived by multiplying the % AFB⁺ cells by the total number of cells in each sample. Results for individual mice are presented as log₁₀ total AFB⁺ cells, with the line representing the mean. (B) The proportion of Mtb-infected phagocytes within the total sample was counted at each time point and expressed as % AFB⁺ cells. (C) Neutrophils infected with Mtb were identified by their typical nuclear morphology on Ziehl-Neelsen stained cytospin slides of BAL cells and whole lung leukocytes. The relative proportion of AFB in neutrophils versus monocytic phagocytes (AM, RM and mDC) is expressed as mean % AFB⁺ leukocytes ± SD from one representative experiment. All in vivo experiments were repeated twice.</p