Atherosclerotic cardiovascular disease is a major cause of death among humans. Animal models have shown that cholesterol and inflammation are causatively involved in the disease process. ...Apolipoprotein B-containing lipoproteins elicit immune reactions and instigate inflammation in the vessel wall. Still, a treatment that is specific to vascular inflammation is lacking, which motivates continued in vivo investigations of the immune-vascular interactions that drive the disease. In this review, we distill old notions with emerging concepts into a contemporary understanding of vascular disease models. Pros and cons of different models are listed and the complex integrative interplay between cholesterol homeostasis, immune activation, and adaptations of the vascular system is discussed. Key limitations with atherosclerosis models are highlighted, and we suggest improvements that could accelerate progress in the field. However, excessively rigid experimental guidelines or limiting usage to certain animal models can be counterproductive. Continued work in improved models, as well as the development of new models, should be of great value in research and could aid the development of cardiovascular disease diagnostics and therapeutics of the future.
Nonresolving inflammation underlies a range of chronic inflammatory diseases, and therapeutic acceleration of resolution of inflammation may improve outcomes. Neural reflexes regulate the intensity ...of inflammation (for example, through signals in the vagus nerve), but whether activation of the vagus nerve promotes the resolution of inflammation in vivo has been unknown. To investigate this, mice were subjected to electrical vagus nerve stimulation (VNS) or sham surgery at the cervical level followed by zymosan-induced peritonitis. The duration of inflammation resolution was significantly reduced and efferocytosis was significantly increased in mice treated with VNS as compared with sham. Lipid mediator (LM) metabololipidomics revealed that mice treated with VNS had higher levels of specialized proresolving mediators (SPMs), particularly from the omega-3 docosahexaenoic (DHA) and docosapentaenoic (n-3 DPA) metabolomes, in peritoneal exudates. VNS also shifted the ratio between proinflammatory and proresolving LMs toward a proresolving profile, but this effect by VNS was inverted in mice deficient in 12/15-lipoxgenase (Alox15), a key enzyme in this SPM biosynthesis. The significant VNS-mediated reduction of neutrophil numbers in peritoneal exudates was absent in mice deficient in the cholinergic α7-nicotinic acetylcholine receptor subunit (α7nAChR), an essential component of the inflammatory reflex. Thus, VNS increased local levels of SPM and accelerated resolution of inflammation in zymosan-induced peritonitis by a mechanism that involves Alox15 and requires the α7nAChR.
Endothelial dysfunction and impaired vasodilation are linked with adverse cardiovascular events. T lymphocytes expressing choline acetyltransferase (ChAT), the enzyme catalyzing biosynthesis of the ...vasorelaxant acetylcholine (ACh), regulate vasodilation and are integral to the cholinergic antiinflammatory pathway in an inflammatory reflex in mice. Here, we found that human T cell ChAT mRNA expression was induced by T cell activation involving the PI3K signaling cascade. Mechanistically, we identified that ChAT mRNA expression was induced following the attenuation of RE-1 Silencing Transcription factor REST-mediated methylation of the ChAT promoter, and that ChAT mRNA expression levels were up-regulated by GATA3 in human T cells. In functional experiments, T cell-derived ACh increased endothelial nitric oxide-synthase activity, promoted vasorelaxation, and reduced vascular endothelial activation and promoted barrier integrity by a cholinergic mechanism. Further, we observed that survival in a cohort of patients with severe circulatory failure correlated with their relative frequency of
T cells in blood. These findings on ChAT
human T cells provide a mechanism for cholinergic immune regulation of vascular endothelial function in human inflammation.
•Cholinergic signals regulate inflammation and vascular function.•ChAT+ T and B cells have the capacity to biosynthesize and release acetylcholine.•ChAT+ T cells regulate immune responses and viral ...clearance.
Recent advances in neuroscience and immunology have shown that cholinergic signals are vital in the regulation of inflammation and immunity. Choline acetyltransferase+ (ChAT+) lymphocytes have the capacity to biosynthesize and release acetylcholine, the cognate ligand for cholinergic receptors. Acetylcholine-producing T cells relay neural signals in the ‘inflammatory reflex’ that regulate cytokine release in spleen. Mice deficient in acetylcholine-producing T cells have increased blood pressure, show reduced local vasodilatation and viral control in lymphocytic choriomeningitis virus infection, and display changes in gut microbiota compared with littermates. These observations indicate that ChAT+ lymphocytes play physiologically important roles in regulation of inflammation and anti-microbial defense. However, the full scope and importance of ChAT+ lymphocytes in immunity and vascular biology remains to be elucidated. Here, we review key findings in this emerging area.
While PAX5 is an important tumor suppressor gene in B‐cell acute lymphoblastic leukemia (B‐ALL), it is also involved in oncogenic translocations coding for diverse PAX5 fusion proteins. PAX5‐JAK2 ...encodes a protein consisting of the PAX5 DNA‐binding region fused to the constitutively active JAK2 kinase domain. Here, we studied the oncogenic function of the PAX5‐JAK2 fusion protein in a mouse model expressing it from the endogenous Pax5 locus, resulting in inactivation of one of the two Pax5 alleles. Pax5Jak2/+ mice rapidly developed an aggressive B‐ALL in the absence of another cooperating exogenous gene mutation. The DNA‐binding function and kinase activity of Pax5‐Jak2 as well as IL‐7 signaling contributed to leukemia development. Interestingly, all Pax5Jak2/+ tumors lost the remaining wild‐type Pax5 allele, allowing efficient DNA‐binding of Pax5‐Jak2. While we could not find evidence for a nuclear role of Pax5‐Jak2 as an epigenetic regulator, high levels of active phosphorylated STAT5 and increased expression of STAT5 target genes were seen in Pax5Jak2/+ B‐ALL tumors, implying that nuclear Pax5‐Jak2 phosphorylates STAT5. Together, these data reveal Pax5‐Jak2 as an important nuclear driver of leukemogenesis by maintaining phosphorylated STAT5 levels in the nucleus.
Synopsis
The oncogenic human PAX5‐JAK2 translocation encodes a protein consisting of the PAX5 DNA‐binding region fused to the constitutively active JAK2 kinase domain. A mouse model shows how this translocation promotes rapid development of aggressive B‐cell acute lymphoblastic leukemia (B‐ALL) in the absence of other exogenous mutations.
Leukemogenesis in Pax5Jak2/+ mice depends on the DNA‐binding function and kinase activity of PAX5‐JAK2 and on IL‐7 signaling.
Rapid tumorigenesis onset correlates with, and is accelerated by, loss of the wild‐type Pax5 allele.
Loss of Pax5 facilitates DNA binding of PAX5‐JAK2.
PAX5‐JAK2 does not act as a transcriptional or epigenetic regulator in the nucleus.
PAX5‐JAK2 is a constitutively‐active nuclear kinase maintaining activation of the transcriptional leukemogenesis driver STAT5.
A mouse model of the oncogenic PAX5‐JAK2 translocation reveals promotion of aggressive B‐ALL not via transcriptional or epigenetic alterations, but via increased phosphorylation and activation of the JAK2 target STAT5.
B cell and plasma cell fates are controlled by different transcriptional networks, as exemplified by the mutually exclusive expression and cross-antagonism of the B cell identity factor Pax5 and the ...plasma cell regulator Blimp1. It has been postulated that repression of Pax5 by Blimp1 is essential for plasma cell development. Here, we challenged this hypothesis by analyzing the IghPax5/+ mouse, which expressed a Pax5 minigene from the immunoglobulin heavy-chain locus. Despite high Pax5 expression, plasma cells efficiently developed in young IghPax5/+ mice at steady state and upon immunization, while their number moderately declined in older mice. Although Pax5 significantly deregulated the plasma cell expression program, key plasma cell regulators were normally expressed in IghPax5/+ plasma cells. While IgM and IgA secretion by IghPax5/+ plasma cells was normal, IgG secretion was modestly decreased. Hence, Pax5 repression is not essential for robust plasma cell development and antibody secretion, although it is required for optimal IgG production and accumulation of long-lived plasma cells.
The transcription factor E2A controls the initiation of B lymphopoiesis, which is arrested at the pre-pro-B cell stage in E2A-deficient mice. Here, we demonstrate by conditional mutagenesis that E2A ...is essential for the development of pro-B, pre-B, and immature B cells in the bone marrow. E2A is, however, dispensable for the generation of mature B cells and plasma cells in peripheral lymphoid organs. In contrast, germinal center B cell development is impaired in the absence of E2A despite normal AID expression and class-switch recombination. Molecular analysis revealed that E2A is required not only for initiating but also for maintaining the expression of
Ebf1,
Pax5, and the B cell gene program in pro-B cells. Notably, precocious
Pax5 transcription from the
Ikzf1 locus promotes pro-B cell development in E2A-deficient mice, demonstrating that ectopic
Pax5 expression is sufficient to activate the B lymphoid transcription program in vivo in the absence of E2A.
Objective
Rheumatoid arthritis (RA) is considered to be a prototypical autoimmune disorder. Several mechanisms have been proposed for the known pathologic function of B cells in RA, including antigen ...presentation, cytokine secretion, and humoral immunity. The aim of this study was to address the function of B lymphocytes in experimental arthritis.
Methods
We mapped the adaptive immune response following collagen‐induced arthritis (CIA). We subsequently monitored these responses and disease outcomes in genetically modified mouse strains that lack mature B cell or germinal center (GC) functionality in a B cell–intrinsic manner.
Results
Following primary immunization, the draining lymph nodes broadly reacted against type II collagen (CII) with the formation of GCs and T cell activation. Mice that lacked mature B cell function were fully protected against CIA and had a severely attenuated ability to mount isotype‐switched humoral immune responses against CII. Almost identical results were observed in mice that were selectively deficient in GC responses. Importantly, GC‐deficient mice were fully susceptible to collagen antibody–induced arthritis.
Conclusion
We identified GC formation and anticollagen antibody production as the key pathogenic functions of B cells in CIA. The role of B cells in RA is likely to be more complex. However, targeting the GC reaction could allow for therapeutic interventions that are more refined than general B cell depletion.
Atherosclerosis progression is modulated by interactions with the adaptive immune system. Humoral immunity can help protect against atherosclerosis formation; however, the existence, origin, and ...function of putative atherogenic antibodies are controversial. How such atherosclerosis-promoting antibodies could affect the specific composition and stability of plaques, as well as the vasculature generally, remains unknown.
We addressed the overall contribution of antibodies to atherosclerosis plaque formation, composition, and stability in vivo (1) with mice that displayed a general loss of antibodies, (2) with mice that had selectively ablated germinal center-derived IgG production, or (3) through interruption of T-B-cell interactions and further studied the effects of antibody deficiency on the aorta by transcriptomics.
Here, we demonstrate that atherosclerosis-prone mice with attenuated plasma cell function manifest reduced plaque burden, indicating that antibodies promote atherosclerotic lesion size. However, the composition of the plaque was altered in antibody-deficient mice, with an increase in lipid content and decreases in smooth muscle cells and macrophages, resulting in an experimentally validated vulnerable plaque phenotype. Furthermore, IgG antibodies enhanced smooth muscle cell proliferation in vitro in an Fc receptor-dependent manner, and antibody-deficient mice had decreased neointimal hyperplasia formation in vivo. These IgG antibodies were shown to be derived from germinal centers, and mice genetically deficient for germinal center formation had strongly reduced atherosclerosis plaque formation. mRNA sequencing of aortas revealed that antibodies are required for the sufficient expression of multiple signal-induced and growth-promoting transcription factors and that aortas undergo large-scale metabolic reprograming in their absence. Using an elastase model, we demonstrated that absence of IgG results in an increased severity of aneurysm formation.
We propose that germinal center-derived IgG antibodies promote the size and stability of atherosclerosis plaques, through promoting arterial smooth muscle cell proliferation and maintaining the molecular identity of the aorta. These results could have implications for therapies that target B cells or B-T-cell interactions because the loss of humoral immunity leads to a smaller but less stable plaque phenotype.
H4K20 methylation is a broad chromatin modification that has been linked with diverse epigenetic functions. Several enzymes target H4K20 methylation, consistent with distinct mono-, di-, and ...trimethylation states controlling different biological outputs. To analyze the roles of H4K20 methylation states, we generated conditional null alleles for the two Suv4-20h histone methyltransferase (HMTase) genes in the mouse. Suv4-20h-double-null (dn) mice are perinatally lethal and have lost nearly all H4K20me3 and H4K20me2 states. The genome-wide transition to an H4K20me1 state results in increased sensitivity to damaging stress, since Suv4-20h-dn chromatin is less efficient for DNA double-strand break (DSB) repair and prone to chromosomal aberrations. Notably, Suv4-20h-dn B cells are defective in immunoglobulin class-switch recombination, and Suv4-20h-dn deficiency impairs the stem cell pool of lymphoid progenitors. Thus, conversion to an H4K20me1 state results in compromised chromatin that is insufficient to protect genome integrity and to process a DNA-rearranging differentiation program in the mouse.
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