Immune profiling of murine cardiac leukocytes identifies triggering receptor expressed on myeloid cells 2 as a novel mediator of hypertensive heart failure.

AIMS: Heart failure with preserved ejection fraction (HFpEF) is characterized by diastolic dysfunction, microvascular dysfunction, and myocardial fibrosis with recent evidence implicating the immune system in orchestrating cardiac remodelling. METHODS AND RESULTS: Here, we show the mouse model of deoxycorticosterone acetate (DOCA)-salt hypertension induces key elements of HFpEF, including diastolic dysfunction, exercise intolerance, and pulmonary congestion in the setting of preserved ejection fraction. A modified single-cell sequencing approach, cellular indexing of transcriptomes and epitopes by sequencing, of cardiac immune cells reveals an altered abundance and transcriptional signature in multiple cell types, most notably cardiac macrophages. The DOCA-salt model results in differential expression of several known and novel genes in cardiac macrophages, including up-regulation of Trem2, which has been recently implicated in obesity and atherosclerosis. The role of Trem2 in hypertensive heart failure, however, is unknown. We found that mice with genetic deletion of Trem2 exhibit increased cardiac hypertrophy, diastolic dysfunction, renal injury, and decreased cardiac capillary density after DOCA-salt treatment compared to wild-type controls. Moreover, Trem2-deficient macrophages have impaired expression of pro-angiogenic gene programmes and increased expression of pro-inflammatory cytokines. Furthermore, we found that plasma levels of soluble TREM2 are elevated in DOCA-salt treated mice and humans with heart failure. CONCLUSIONS: Together, our data provide an atlas of immunological alterations that can lead to improved diagnostic and therapeutic strategies for HFpEF. We provide our dataset in an easy to explore and freely accessible web application making it a useful resource for the community. Finally, our results suggest a novel cardioprotective role for Trem2 in hypertensive heart failure.

Reduced Circumferential Strain in Athletes with Prior COVID-19.

Purpose: To characterize global and segmental circumferential systolic strain (CS) measured by cardiac MRI in athletes after SARS-CoV-2 infection. Materials and Methods: This retrospective observational cohort study included 188 soldiers and collegiate athletes referred for cardiac MRI after SARS-CoV-2 infection (C19+) between July 2020 and February 2021 and a control group of 72 soldiers, collegiate, and high school athletes who underwent cardiac MRI from May 2019 to February 2020, prior to the first SARS-CoV-2 case detected in our region (C19-). Global and segmental CS were measured by feature tracking, then compared between each group using unadjusted and multivariable- adjusted models. Acute myocarditis was diagnosed according to the modified Lake Louise criteria and the location of pathologic late gadolinium enhancement (LGE) was ascertained. Results: Among the 188 C19+ athletes (median age, 25 years [IQR, 23-30]; 131 men), the majority had mild illness. Global CS significantly differed between C19+ and C19- groups, with a median of -24.0 (IQR -25.8, -21.4) versus. -25.0 (-28.0, -22.4), respectively (p = .009). This difference in CS persisted following adjustment for age, sex, body mass index, heart rate, and systolic blood pressure ß coefficient 1.29 [95% CI: 0.20, 2.38], p = .02). In segmental analysis, the basal- and mid- inferoseptal, septal and inferolateral segments were significantly different (p < .05), which had a higher frequency of post-COVID late gadolinium enhancement. The global and segmental differences were similar after exclusion of athletes with myocarditis. Conclusion: Among athletes, SARS-CoV-2 infection was associated with a small but statistically significant reduced CS.

Cardiovascular magnetic resonance evaluation of soldiers after recovery from symptomatic SARS-CoV-2 infection: a case-control study of cardiovascular post-acute sequelae of SARS-CoV-2 infection (CV PASC).

BACKGROUND: Myocarditis is a potential complication after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and a known cause of sudden cardiac death. Given the athletic demands of soldiers, identification of myocarditis and characterization of post-acute sequelae of SARS-CoV-2 infection with cardiovascular symptoms (CV PASC) may be critical to guide return-to-service. This study sought to evaluate the spectrum of cardiac involvement among soldiers with cardiopulmonary symptoms in the late convalescent phase of recovery from SARS-CoV-2 compared to a healthy soldier control group, and to determine the rate of progression to CV PASC. METHODS: All soldiers referred for cardiovascular magnetic resonance (CMR) imaging for cardiopulmonary symptoms following COVID-19 were enrolled and matched by age, gender, and athletic phenotype 1:1 to soldiers undergoing CMR in the year prior to the first case of COVID-19 at our institution. Demographic, clinical, laboratory, and imaging parameters were compared between groups. The diagnosis of acute myocarditis was made using modified Lake Louise criteria. Wilcoxon rank sum and chi-squared tests were used for comparison of continuous and categorical variables, respectively. RESULTS: Fifty soldier cases and 50 healthy soldier controls were included. The median time from SARS-CoV-2 detection to CMR was 71 days. The majority of cases experienced moderate symptoms (N = 43, 86%), while only 10% required hospitalization. The right ventricular (RV) ejection fraction (RVEF) was reduced in soldier cases compared to controls (51.0% vs. 53.2%, p = 0.012). Four cases were diagnosed with myocarditis (8%), 1 (2%) was diagnosed with Takotsubo cardiomyopathy, and 1 (2%) had new biventricular systolic dysfunction of unclear etiology. Isolated inferior RV septal insertion late gadolinium enhancement (LGE) was present in 8 cases and 8 controls (16% vs. 24%, p = 0.09). Seven of the 19 (37%) cases that completed an intermediate-term follow-up survey reported CV PASC at a median of 139 days of follow-up. Two of the 7 soldiers (29%) with CV PASC had a pathological clinical diagnosis (myocarditis) on CMR. CONCLUSIONS: Cardiovascular pathology was diagnosed in 6 symptomatic soldiers (12%) after recovery from SARS-CoV-2, with myocarditis found in 4 (8%). RVEF was reduced in soldier cases compared to controls. CV PASC occurred in over one-third of soldiers surveyed, but did not occur in any soldiers with asymptomatic acute SARS-CoV-2 infection.

Modulating In Vivo Degradation Rate of Injectable Extracellular Matrix Hydrogels.

Extracellular matrix (ECM) derived hydrogels are increasingly used as scaffolds to stimulate endogenous repair. However, few studies have examined how altering the degradation rates of these materials affect cellular interaction in vivo. This study sought to examine how crosslinking or matrix metalloproteinase (MMP) inhibition by doxycycline could be employed to modulate the degradation rate of an injectable hydrogel derived from decellularized porcine ventricular myocardium. While both approaches were effective in reducing degradation in vitro, only doxycycline significantly prolonged hydrogel degradation in vivo without affecting material biocompatibility. In addition, unlike crosslinking, incorporation of doxycycline into the hydrogel did not affect mechanical properties. Lastly, the results of this study highlighted the need for development of novel crosslinkers for in situ modification of injectable ECM-derived hydrogels, as none of the crosslinking agents investigated in this study were both biocompatible and effective.

Evidence for Mechanisms Underlying the Functional Benefits of a Myocardial Matrix Hydrogel for Post-MI Treatment.

BACKGROUND: There is increasing need for better therapies to prevent the development of heart failure after myocardial infarction (MI). An injectable hydrogel derived from decellularized porcine ventricular myocardium has been shown to halt the post-infarction progression of negative left ventricular remodeling and decline in cardiac function in both small and large animal models. OBJECTIVES: This study sought to elucidate the tissue-level mechanisms underlying the therapeutic benefits of myocardial matrix injection. METHODS: Myocardial matrix or saline was injected into infarcted myocardium 1 week after ischemia-reperfusion in Sprague-Dawley rats. Cardiac function was evaluated by magnetic resonance imaging and hemodynamic measurements at 5 weeks after injection. Whole transcriptome microarrays were performed on RNA isolated from the infarct at 3 days and 1 week after injection. Quantitative polymerase chain reaction and histologic quantification confirmed expression of key genes and their activation in altered pathways. RESULTS: Principal component analysis of the transcriptomes showed that samples collected from myocardial matrix-injected infarcts are distinct and cluster separately from saline-injected control subjects. Pathway analysis indicated that these differences are due to changes in several tissue processes that may contribute to improved cardiac healing after MI. Matrix-injected infarcted myocardium exhibits an altered inflammatory response, reduced cardiomyocyte apoptosis, enhanced infarct neovascularization, diminished cardiac hypertrophy and fibrosis, altered metabolic enzyme expression, increased cardiac transcription factor expression, and progenitor cell recruitment, along with improvements in global cardiac function and hemodynamics. CONCLUSIONS: These results indicate that the myocardial matrix alters several key pathways after MI creating a pro-regenerative environment, further demonstrating its promise as a potential post-MI therapy.

Decellularized skeletal muscle as an in vitro model for studying drug-extracellular matrix interactions.

Several factors can affect drug absorption after intramuscular (IM) injection: drug solubility, drug transport across cell membranes, and drug metabolism at the injection site. We found that potential interactions between the drug and the extracellular matrix (ECM) at the injection site can also affect the rate of absorption post-injection. Using decellularized skeletal muscle, we developed a simple method to model drug absorption after IM injection, and showed that the nature of the drug-ECM interaction could be investigated by adding compounds that alter binding. We validated the model using the vitamin B12 analog cobinamide with different bound ligands. Cobinamide is being developed as an IM injectable treatment for cyanide poisoning, and we found that the in vitro binding data correlated with previously published in vivo drug absorption in animals. Commercially available ECM products, such as collagen and GelTrex, did not recapitulate drug binding behavior. While decellularized ECM has been widely studied in fields such as tissue engineering, this work establishes a novel use of skeletal muscle ECM as a potential in vitro model to study drug-ECM interactions during drug development.