Allen J. York

Rationale: The adult cardiac extracellular matrix (ECM) is largely comprised of type I collagen. In addition to serving as the primary structural support component of the cardiac ECM, type I collagen also provides an organizational platform for other ECM proteins, matricellular proteins, and signaling components that impact cellular stress sensing in vivo. Objective: Here we investigated how the content and integrity of type I collagen affect cardiac structure function and response to injury. Methods and Results: We generated and characterized Col1a2^−/− mice using standard gene targeting. Col1a2^−/− mice were viable, although by young adulthood their hearts showed alterations in ECM mechanical properties, as well as an unanticipated activation of cardiac fibroblasts and induction of a progressive fibrotic response. This included augmented TGFβ activity, increases in fibroblast number, and progressive cardiac hypertrophy, with reduced functional performance by 9 months of age. Col1a2-loxP-targeted mice were also generated and crossed with the tamoxifen-inducible Postn-MerCreMer mice to delete the Col1a2 gene in myofibroblasts with pressure overload injury. Interestingly, while germline Col1a2^−/− mice showed gradual pathologic hypertrophy and fibrosis with aging, the acute deletion of Col1a2 from activated adult myofibroblasts showed a loss of total collagen deposition with acute cardiac injury and an acute reduction in pressure overload-induce cardiac hypertrophy. However, this reduction in hypertrophy due to myofibroblast-specific Col1a2 deletion was lost after 2 and 6 weeks of pressure overload, as fibrotic deposition accumulated. Conclusions: Defective type I collagen in the heart alters the structural integrity of the ECM and leads to cardiomyopathy in adulthood, with fibroblast expansion, activation, and alternate fibrotic ECM deposition. However, acute inhibition of type I collagen production can have an anti-fibrotic and anti-hypertrophic effect.

Mitochondrial permeability transition pore (MPTP) formation contributes to ischemia-reperfusion injury in the heart and several degenerative diseases, including muscular dystrophy (MD). MD is a family of genetic disorders characterized by progressive muscle necrosis and premature death. It has been proposed that the MPTP has two molecular components, the adenine nucleotide translocase (ANT) family of proteins and an unknown component that requires the chaperone cyclophilin D (CypD) to activate. This model was examined in vivo by deleting the gene encoding ANT1 ( Slc25a4 ) or CypD ( Ppif ) in a δ-sarcoglycan ( Sgcd ) gene–deleted mouse model of MD, revealing that dystrophic mice lacking Slc25a4 were partially protected from cell death and MD pathology. Dystrophic mice lacking both Slc25a4 and Ppif together were almost completely protected from necrotic cell death and MD disease. This study provides direct evidence that ANT1 and CypD are required MPTP components governing in vivo cell death, suggesting a previously unrecognized therapeutic approach in MD and other necrotic diseases.

The world is currently in a pandemic of COVID-19 (Coronavirus disease-2019) caused by a novel positive-sense, single-stranded RNA β-coronavirus referred to as SARS-CoV-2. Here we investigated rates of SARS-CoV-2 infection in the greater Cincinnati, Ohio, USA metropolitan area from August 13 to December 8, 2020, just prior to initiation of the national vaccination program. Examination of 9,550 adult blood donor volunteers for serum IgG antibody positivity against the SARS-CoV-2 Spike protein showed an overall prevalence of 8.40%, measured as 7.56% in the first 58 days and 9.24% in the last 58 days, and 12.86% in December 2020, which we extrapolated to ~20% as of March, 2021. Males and females showed similar rates of past infection, and rates among Hispanic or Latinos, African Americans and Whites were also investigated. Donors under 30 years of age had the highest rates of past infection, while those over 60 had the lowest. Geographic analysis showed higher rates of infectivity on the West side of Cincinnati compared with the East side (split by I-75) and the lowest rates in the adjoining region of Kentucky (across the Ohio river). These results in regional seroprevalence will help inform efforts to best achieve herd immunity in conjunction with the national vaccination campaign.

Background: Pulmonary hypertension (PH) is a common complication in patients with alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV), a severe congenital disorder associated with mutations in the FOXF1 gene. Although the loss of alveolar microvasculature causes PH in patients with ACDMPV, it is unknown whether increasing neonatal lung angiogenesis could prevent PH and right ventricular (RV) hypertrophy. Methods: We used echocardiography, RV catheterization, immunostaining, and biochemical methods to examine lung and heart remodeling and RV output in Foxf1 ^WT/S52F mice carrying the S52F Foxf1 mutation (identified in patients with ACDMPV). The ability of Foxf1 ^WT/S52F mutant embryonic stem cells to differentiate into respiratory cell lineages in vivo was examined using blastocyst complementation. Intravascular delivery of nanoparticles with a nonintegrating Stat3 expression vector was used to improve neonatal pulmonary angiogenesis in Foxf1 ^WT/S52F mice and determine its effects on PH and RV hypertrophy. Results: Foxf1 ^WT/S52F mice developed PH and RV hypertrophy after birth. The severity of PH in Foxf1 ^WT/S52F mice directly correlated with mortality, low body weight, pulmonary artery muscularization, and increased collagen deposition in the lung tissue. Increased fibrotic remodeling was found in human ACDMPV lungs. Mouse embryonic stem cells carrying the S52F Foxf1 mutation were used to produce chimeras through blastocyst complementation and to demonstrate that Foxf1 ^WT/S52F embryonic stem cells have a propensity to differentiate into pulmonary myofibroblasts. Intravascular delivery of nanoparticles carrying Stat3 cDNA protected Foxf1 ^WT/S52F mice from RV hypertrophy and PH, improved survival, and decreased fibrotic lung remodeling. Conclusions: Nanoparticle therapies increasing neonatal pulmonary angiogenesis may be considered to prevent PH in ACDMPV.

Clinical trials using adult stem cells to regenerate damaged heart tissue continue to this day ^1–3 despite ongoing questions of efficacy and a lack of mechanistic understanding of the underlying biologic effect ^4–6 . The rationale for these cell therapy trials is derived from animal studies that show a modest but reproducible improvement in cardiac function in models of cardiac ischemic injury ^7–9 . Here we examined the mechanistic basis for cell therapy in mice after ischemia/reperfusion (I/R) injury, and while heart function was enhanced, it was not associated with new cardiomyocyte production. Cell therapy improved heart function through an acute sterile immune response characterized by the temporal and regional induction of CCR2 ⁺ and CX3CR1 ⁺ macrophages. Here we observed that intra-cardiac injection of 2 distinct types of progenitor cells, freeze/thaw-killed cells or a chemical inducer of the innate immune response similarly induced regional CCR2 ⁺ and CX3CR1 ⁺ macrophage accumulation and provided functional rejuvenation to the I/R-injured heart. Mechanistically, this selective macrophage response altered cardiac fibroblast activity and reduced border zone extracellular matrix (ECM) content and enhanced the mechanical properties of the injured area. The functional benefit of cardiac cell therapy is thus due to an acute inflammatory-based wound healing response that rejuvenates the mechanical properties of the infarcted area of the heart. Such results suggest a re-evaluation of strategies underlying cardiac cell therapy in current and planned human clinical trials.