Over but not gone: lingering epigenetic effects of COVID-19

'Long COVID' affects nearly one in five adults who have had coronavirus disease 2019 (COVID-19), yet the mechanisms underlying this disorder remain poorly understood. In a new study, Cheong et al. show that the epigenetic and transcriptional state of myeloid immune cells and their progenitors are durably altered in patients following severe COVID-19.

Hematopoietic stem and progenitor cells confer cross-protective trained immunity in mouse models

Recent studies suggest that infection reprograms hematopoietic stem and progenitor cells (HSPCs) to enhance innate immune responses upon secondary infectious challenge, a process called "trained immunity." However, the specificity and cell types responsible for this response remain poorly defined. We established a model of trained immunity in mice in response to Mycobacterium avium infection. scRNA-seq analysis revealed that HSPCs activate interferon gamma-response genes heterogeneously upon primary challenge, while rare cell populations expand. Macrophages derived from trained HSPCs demonstrated enhanced bacterial killing and metabolism, and a single dose of recombinant interferon gamma exposure was sufficient to induce similar training. Mice transplanted with influenza-trained HSPCs displayed enhanced immunity against M. avium challenge and vice versa, demonstrating cross protection against antigenically distinct pathogens. Together, these results indicate that heterogeneous responses to infection by HSPCs can lead to long-term production of bone marrow derived macrophages with enhanced function and confer cross-protection against alternative pathogens.

BATF2 promotes HSC myeloid differentiation by amplifying IFN response mediators during chronic infection

Basic leucine zipper ATF-like transcription factor 2 (BATF2), an interferon-activated immune response regulator, is a key factor responsible for myeloid differentiation and depletion of HSC during chronic infection. To delineate the mechanism of BATF2 function in HSCs, we assessed Batf2 KO mice during chronic infection and found that they produced less pro-inflammatory cytokines, less immune cell recruitment to the spleen, and impaired myeloid differentiation with better preservation of HSC capacity compared to WT. Co-IP analysis revealed that BATF2 forms a complex with JUN to amplify pro-inflammatory signaling pathways including CCL5 during infection. Blockade of CCL5 receptors phenocopied Batf2 KO differentiation defects, whereas treatment with recombinant CCL5 was sufficient to rescue IFNγ-induced myeloid differentiation and recruit more immune cells to the spleen in Batf2 KO mice. By revealing the mechanism of BATF2-induced myeloid differentiation of HSCs, these studies elucidate potential therapeutic strategies to boost immunity while preserving HSC function during chronic infection.

Clonal hematopoiesis: Mutation-specific adaptation to environmental change

Clonal hematopoiesis of indeterminate potential (CHIP) describes a widespread expansion of genetically variant hematopoietic cells that increases exponentially with age and is associated with increased risks of cancers, cardiovascular disease, and other maladies. Here, we discuss how environmental contexts associated with CHIP, such as old age, infections, chemotherapy, or cigarette smoking, alter tissue microenvironments to facilitate the selection and expansion of specific CHIP mutant clones. Further, we consider major remaining gaps in knowledge, including intrinsic effects, clone size thresholds, and factors affecting clonal competition, that will determine future application of this field in transplant and preventive medicine.

Statins and risk of cancer: A meta-analysis of randomized, double-blind, placebo-controlled trials

PURPOSE

Several meta-analyses of randomized controlled trials (RCTs) reported no association between the use of statins and the risk of cancer. However, they included open-label RCTs, which did not use placebo as a control group. This study aimed to evaluate the effect of statins on cancer risk using a meta-analysis of randomized, double-blind, placebo-controlled trials (RDBPCTs).

METHODS

We searched PubMed, EMBASE, and the Cochrane Library in March 2016. Two individual authors reviewed and selected RDBPCTs based on selection criteria.

RESULTS

Out of 676 retrieved articles, a total of 21 RDBPCTs with 65,196 participants (32,618 in the statin group and 32,578 in the placebo group) were included in the meta-analysis. Overall, we found that there was no significant association between the use of statins and the risk of cancer (relative risk 0.97, 95% confidence interval 0.92-1.02, I² = 0.0%) in a fixed-effect meta-analysis. In addition, in the subgroup meta-analyses, no beneficial effect of statins was observed when analyzed by statin type, country, follow-up period, methodological quality, underlying diseases/population, and type of cancer.

CONCLUSIONS

The current meta-analysis of RDBPCTs found that there was no association between the use of statins and the risk of cancer.

Relative contribution of vasodilator prostanoids and NO to metabolic vasodilation in the human forearm

Although many factors are thought to contribute to the regulation of metabolic vasodilation in skeletal muscle vasculature, recent interest has focused on the role of the endothelium. We examined the relative roles of nitric oxide (NO) and of vasodilator prostanoids in the control of metabolically induced functional hyperemia in the forearm of humans. In 43 healthy volunteers [24 +/- 5 (SD) yr] we assessed resting and functional hyperemic blood flow (FHBF) in response to 2 min of isotonic forearm exercise before and after inhibition of NO and/or vasodilator prostanoid production with intra-arterial NG-monomethyl-L-arginine (L-NMMA, 2 mg/min) and aspirin (ASA, 3 mg/min), respectively. Blood flow was measured using venous occlusion plethysmography. L-NMMA and ASA decreased resting forearm blood flow by 42% (P < 0.0001) and 23% (P < 0.0001), respectively, whereas infusion of ASA followed by L-NMMA reduced flow by a further 24% (P < 0.05). L-NMMA reduced peak FHBF by 18% [from 13.9 +/- 1.0 to 11.4 +/- 1.1 (SE) ml. 100 ml forearm-1. min-1, P = 0.003] and the volume "repaid" after 1 and 5 min by 25% (8.9 +/- 0.7 vs. 6.7 +/- 0.7 ml/100 ml, P < 0.0001) and 37% (26.6 +/- 1.8 vs. 16.8 +/- 1.6 ml/100 ml, P < 0.0001). ASA similarly reduced peak FHBF by 19% (from 14.5 +/- 1.1 to 11.8 +/- 0.9. 100 ml forearm-1. min-1, P < 0.001) and the volume repaid after 1 and 5 min by 14% (7.5 +/- 0. 6 vs. 6.4 +/- 0.6 ml/100 ml, P = 0.0001) and 20% (21.2 +/- 1.5 vs. 16.9 +/- 1.5 ml/100 ml, P < 0.0001), respectively. The coinfusion of ASA and L-NMMA did not decrease FHBF to a greater extent than either agent alone. These data suggest that endothelium-derived NO and vasodilator prostanoids contribute to resting blood flow and metabolic vasodilation in skeletal muscle vasculature in healthy humans. Although these vasodilator mechanisms operate in parallel in exercise-induced hyperemia, they appear not to be additive. Other mechanisms must also be operative in metabolic vasodilation.

Continuous release of vasodilator prostanoids contributes to regulation of resting forearm blood flow in humans

Continuous release of nitric oxide contributes to the maintenance of resting tone in the human forearm and coronary circulations; however, evidence for a similar role of vasodilator prostanoids such as prostacyclin is lacking. We examined whether continuous release of prostacyclin contributes to basal forearm blood flow. Flow was measured using venous occlusion plethysmography in 38 healthy volunteers [mean age 21.3 +/- 2.5 yr (+/- SD); 13 female, 25 male] at rest, after administration of three incremental intra-arterial infusions of either the cyclooxygenase inhibitor aspirin or placebo, and before and after administration of the endothelium-dependent and -independent dilators acetylcholine (30 micrograms/min) and nitroprusside (1 microgram/min). To assess the effect of aspirin on the production of prostacyclin, plasma 6-keto prostaglandin F1 alpha (6-keto-PGF1 alpha; the stable metabolite of prostacyclin) was measured by simultaneous arterial and venous sampling. Aspirin produced a time- and dose-dependent reduction in forearm blood flow, resulting in a 32% decrease at the highest dose. The effect was maximal after 10 min. Flow at rest and after aspirin doses of 1, 3, and 10 mg/min was 2.6 +/- 0.2, 2.3 +/- 0.2, 2.1 +/- 0.2, and 1.8 +/- 0.2 ml.100 ml forearm tissue-1.min-1, respectively (means +/- SE, P < 0.001). Commensurate with these data, the net forearm production of 6-keto-PGF1 alpha was 52.9 +/- 16.4, 11.7 +/- 8.6, 18.7 +/- 8.5, and 12.0 +/- 12.5 pg.100 ml forearm tissue-1.min-1 for the respective doses (P = 0.04). No time-dependent reduction in flow was seen in subjects with vehicle infusion. Aspirin did not affect the responses to acetylcholine or nitroprusside. These data suggest that continuous release of prostacyclin plays a role in the maintenance of resting forearm blood flow. There appears to be a direct link between the reduction in flow with aspirin and inhibition of prostacyclin production.

Long-term estrogen therapy improves vascular function in male to female transsexuals

OBJECTIVES

This study sought to examine the effects of long-term estrogen therapy on vascular function in male to female transsexuals and to compare the findings with those observed in men and premenopausal women.

BACKGROUND

Gender differences in coronary artery disease have largely been attributed to the beneficial effects of estrogen on vascular function and plasma lipids in women. However, the effects of estrogen on the male vasculature have not been widely studied.

METHODS

We compared the effects of estrogen on vascular function in 14 male to female transsexuals, 14 age-matched men and 15 premenopausal women. Flow-mediated vasodilation and response to nitroglycerin were assessed in the brachial artery using noninvasive ultrasound.

RESULTS

Flow-mediated vasodilation was similar in transsexuals and women but greater than that in men ([mean +/- SE] 11.5 +/- 1.3% and 9.4 +/- 1.1% vs. 5.2 +/- 1.0% respectively, p < 0.005). Responses to nitroglycerin were also greater in transsexuals and women than in men (21.6 +/- 1.7% and 21.0 +/- 0.9% vs. 14.5 +/- 1.2%, respectively, p = 0.0005). These differences persisted even after adjusting for vessel size. Despite similar total cholesterol levels, transsexuals had high density lipoprotein cholesterol levels similar to those in women and greater than those observed in men (1.76 +/- 0.12 and 1.82 +/- 0.11 mmol/liter vs. 1.35 +/- 0.07 mmol/liter, respectively, p < 0.005). Moreover, triglyceride levels were greater in transsexuals than in men and women, and low density lipoprotein cholesterol (LDL-C) particle size was smaller (25.7 +/- 0.2 nm vs. 26.2 +/- 0.1 and 26.6 +/- 0.1 nm, respectively, p = 0.0001). Serum testosterone (an index of estrogen therapy in transsexuals) was markedly suppressed in transsexuals and similar to that in women. Univariate analysis revealed that there was a strong inverse correlation between serum testosterone and flow-mediated vasodilation (r(s) = -0.48, p < 0.005). Multivariate analysis revealed that the best combination of predictors of flow-mediated vasodilation was serum testosterone, vessel size and LDL-C (R2 = 0.3, p < 0.005).

CONCLUSIONS

Long-term estrogen therapy appears to improve vascular function in male to female transsexuals and occurs despite higher triglyceride levels and the presence of small, dense LDL-C. The beneficial effects of estrogen are not gender specific or solely mediated through endothelium-derived nitric oxide.