Repairing the lungs one breath at a time: How dedicated or facultative are you?

Tissue regeneration involves various types of cellular and molecular responses depending on the type of tissue and the injury or disease that is inflicted. While many tissues contain dedicated stem/progenitor cell lineages, many others contain cells that, during homeostasis, are considered physiologically functional and fully differentiated but, after injury or in disease states, exhibit stem/progenitor-like activity. Recent identification of subsets of defined cell types as facultative stem/progenitor cells has led to a re-examination of how certain tissues respond to injury to mount a regenerative response. In this review, we focus on lung regeneration to explore the importance of facultative regeneration controlled by functional and differentiated cell lineages as well as how they are positioned and regulated by distinct tissue niches. Additionally, we discuss the molecular signals to which cells respond in their differentiated state during homeostasis and those signals that promote effective regeneration of damaged or lost cells and structures after injury.

Disruption of proteostasis causes IRE1 mediated reprogramming of alveolar epithelial cells.

Disruption of alveolar type 2 cell (AEC2) protein quality control has been implicated in chronic lung diseases, including pulmonary fibrosis (PF). We previously reported the in vivo modeling of a clinical surfactant protein C (SP-C) mutation that led to AEC2 endoplasmic reticulum (ER) stress and spontaneous lung fibrosis, providing proof of concept for disruption to proteostasis as a proximal driver of PF. Using two clinical SP-C mutation models, we have now discovered that AEC2s experiencing significant ER stress lose quintessential AEC2 features and develop a reprogrammed cell state that heretofore has been seen only as a response to lung injury. Using single-cell RNA sequencing in vivo and organoid-based modeling, we show that this state arises de novo from intrinsic AEC2 dysfunction. The cell-autonomous AEC2 reprogramming can be attenuated through inhibition of inositol-requiring enzyme 1 (IRE1α) signaling as the use of an IRE1α inhibitor reduced the development of the reprogrammed cell state and also diminished AEC2-driven recruitment of granulocytes, alveolitis, and lung injury. These findings identify AEC2 proteostasis, and specifically IRE1α signaling through its major product XBP-1, as a driver of a key AEC2 phenotypic change that has been identified in lung fibrosis.

Hippo pathway deficiency reverses systolic heart failure after infarction.

Mammalian organs vary widely in regenerative capacity. Poorly regenerative organs, such as the heart are particularly vulnerable to organ failure. Once established, heart failure commonly results in mortality. The Hippo pathway, a kinase cascade that prevents adult cardiomyocyte proliferation and regeneration, is upregulated in human heart failure. Here we show that deletion of the Hippo pathway component Salvador (Salv) in mouse hearts with established ischaemic heart failure after myocardial infarction induces a reparative genetic program with increased scar border vascularity, reduced fibrosis, and recovery of pumping function compared with controls. Using translating ribosomal affinity purification, we isolate cardiomyocyte-specific translating messenger RNA. Hippo-deficient cardiomyocytes have increased expression of proliferative genes and stress response genes, such as the mitochondrial quality control gene, Park2. Genetic studies indicate that Park2 is essential for heart repair, suggesting a requirement for mitochondrial quality control in regenerating myocardium. Gene therapy with a virus encoding Salv short hairpin RNA improves heart function when delivered at the time of infarct or after ischaemic heart failure following myocardial infarction was established. Our findings indicate that the failing heart has a previously unrecognized reparative capacity involving more than cardiomyocyte renewal.

A steroid receptor coactivator stimulator (MCB-613) attenuates adverse remodeling after myocardial infarction.

Progressive remodeling of the heart, resulting in cardiomyocyte (CM) loss and increased inflammation, fibrosis, and a progressive decrease in cardiac function, are hallmarks of myocardial infarction (MI)-induced heart failure. We show that MCB-613, a potent small molecule stimulator of steroid receptor coactivators (SRCs) attenuates pathological remodeling post-MI. MCB-613 decreases infarct size, apoptosis, hypertrophy, and fibrosis while maintaining significant cardiac function. MCB-613, when given within hours post MI, induces lasting protection from adverse remodeling concomitant with: 1) inhibition of macrophage inflammatory signaling and interleukin 1 (IL-1) signaling, which attenuates the acute inflammatory response, 2) attenuation of fibroblast differentiation, and 3) promotion of Tsc22d3-expressing macrophages-all of which may limit inflammatory damage. SRC stimulation with MCB-613 (and derivatives) is a potential therapeutic approach for inhibiting cardiac dysfunction after MI.

Long-range Pitx2c enhancer-promoter interactions prevent predisposition to atrial fibrillation.

Genome-wide association studies found that increased risk for atrial fibrillation (AF), the most common human heart arrhythmia, is associated with noncoding sequence variants located in proximity to PITX2 Cardiomyocyte-specific epigenomic and comparative genomics uncovered 2 AF-associated enhancers neighboring PITX2 with varying conservation in mice. Chromosome conformation capture experiments in mice revealed that the Pitx2c promoter directly contacted the AF-associated enhancer regions. CRISPR/Cas9-mediated deletion of a 20-kb topologically engaged enhancer led to reduced Pitx2c transcription and AF predisposition. Allele-specific chromatin immunoprecipitation sequencing on hybrid heterozygous enhancer knockout mice revealed that long-range interaction of an AF-associated region with the Pitx2c promoter was required for maintenance of the Pitx2c promoter chromatin state. Long-range looping was mediated by CCCTC-binding factor (CTCF), since genetic disruption of the intronic CTCF-binding site caused reduced Pitx2c expression, AF predisposition, and diminished active chromatin marks on Pitx2 AF risk variants located at 4q25 reside in genomic regions possessing long-range transcriptional regulatory functions directed at PITX2.

Cardiomyocyte Proliferation for Therapeutic Regeneration.

PURPOSE OF REVIEW: Current pharmacologic treatments for cardiovascular disease do not correct the underlying cellular defect, the loss of cardiomyocytes. With recent advancements in cardiac regenerative approaches, the induction of endogenous mature cardiomyocyte proliferation has emerged as a new possibility. Here, we review progress made toward the regeneration of cardiac tissue in the mammalian heart through the stimulation of mature cardiomyocyte renewal. RECENT FINDINGS: The targeting of several developmental and signaling pathways has been shown to stimulate cell cycle re-entry in mature cardiomyocytes. In animal models of cardiac regeneration, various strategies have been used to target these pathways to stimulate cardiomyocyte renewal and have relied on the delivery of signaling factors via systemic delivery, epicardial patches, or direct intramyocardial injection. Gene therapy techniques involving the viral delivery of transgenes by using adenoviral or adeno-associated viral vectors have been used to successfully target cardiac gene expression. The delivery of nucleic acids in the form of anti-microRNAs and microRNA mimetics has also been shown to be effective in stimulating cardiomyocyte renewal. As the field of cardiac regeneration continues to progress, an important ongoing challenge in developing clinically translatable therapies is limiting the stimulation of growth pathways in non-cardiomyocytes.

After sudden unexpected death in epilepsy: Lessons learned and the road forward.

The devastating effects of sudden unexpected death in epilepsy (SUDEP) can be difficult to navigate, even for experienced clinicians. Mounting evidence supports full disclosure of the risks of epilepsy to those affected and their caregivers, and recommendations from regulatory and professional groups encourage the same. Following a death, families are faced with tragedy, guilt, and sometimes anger. Clinicians are often called upon to provide information and support. The development of a comprehensive approach to SUDEP education requires careful consideration of the people living with epilepsy, facts about SUDEP and known risk factors, as well as experiences of families and care providers. In this article, we share the experiences of those working in SUDEP education and epilepsy care, including the voluntary sector. We explore the experience of bereaved families and clinicians, derive lessons from published research, highlight areas where more research is needed, and report on preliminary data from a nationwide study from France.

Temporal and spatial staging of lung alveolar regeneration is determined by the grainyhead transcription factor Tfcp2l1.

Alveolar epithelial type 2 (AT2) cells harbor the facultative progenitor capacity in the lung alveolus to drive regeneration after lung injury. Using single-cell transcriptomics, software-guided segmentation of tissue damage, and in vivo mouse lineage tracing, we identified the grainyhead transcription factor cellular promoter 2-like 1 (Tfcp2l1) as a regulator of this regenerative process. Tfcp2l1 loss in adult AT2 cells inhibits self-renewal and enhances AT2-AT1 differentiation during tissue regeneration. Conversely, Tfcp2l1 blunts the proliferative response to inflammatory signaling during the early acute injury phase. Tfcp2l1 temporally regulates AT2 self-renewal and differentiation in alveolar regions undergoing active regeneration. Single-cell transcriptomics and lineage tracing reveal that Tfcp2l1 regulates cell fate dynamics across the AT2-AT1 differentiation and restricts the inflammatory program in murine AT2 cells. Organoid modeling shows that Tfcp2l1 regulation of interleukin-1 (IL-1) receptor expression controlled these cell fate dynamics. These findings highlight the critical role Tfcp2l1 plays in balancing epithelial cell self-renewal and differentiation during alveolar regeneration.

Gene therapy knockdown of Hippo signaling induces cardiomyocyte renewal in pigs after myocardial infarction.

Human heart failure, a leading cause of death worldwide, is a prominent example of a chronic disease that may result from poor cell renewal. The Hippo signaling pathway is an inhibitory kinase cascade that represses adult heart muscle cell (cardiomyocyte) proliferation and renewal after myocardial infarction in genetically modified mice. Here, we investigated an adeno-associated virus 9 (AAV9)-based gene therapy to locally knock down the Hippo pathway gene Salvador (Sav) in border zone cardiomyocytes in a pig model of ischemia/reperfusion-induced myocardial infarction. Two weeks after myocardial infarction, when pigs had left ventricular systolic dysfunction, we administered AAV9-Sav-short hairpin RNA (shRNA) or a control AAV9 viral vector carrying green fluorescent protein (GFP) directly into border zone cardiomyocytes via catheter-mediated subendocardial injection. Three months after injection, pig hearts treated with a high dose of AAV9-Sav-shRNA exhibited a 14.3% improvement in ejection fraction (a measure of left ventricular systolic function), evidence of cardiomyocyte division, and reduced scar sizes compared to pigs receiving AAV9-GFP. AAV9-Sav-shRNA-treated pig hearts also displayed increased capillary density and reduced cardiomyocyte ploidy. AAV9-Sav-shRNA gene therapy was well tolerated and did not induce mortality. In addition, liver and lung pathology revealed no tumor formation. Local delivery of AAV9-Sav-shRNA gene therapy to border zone cardiomyocytes in pig hearts after myocardial infarction resulted in tissue renewal and improved function and may have utility in treating heart failure.

Age-dependent alveolar epithelial plasticity orchestrates lung homeostasis and regeneration.

Regeneration of the architecturally complex alveolar niche of the lung requires precise temporal and spatial control of epithelial cell behavior. Injury can lead to a permanent reduction in gas exchange surface area and respiratory function. Using mouse models, we show that alveolar type 1 (AT1) cell plasticity is a major and unappreciated mechanism that drives regeneration, beginning in the early postnatal period during alveolar maturation. Upon acute neonatal lung injury, AT1 cells reprogram into alveolar type 2 (AT2) cells, promoting alveolar regeneration. In contrast, the ability of AT2 cells to regenerate AT1 cells is restricted to the mature lung. Unbiased genomic assessment reveals that this previously unappreciated level of plasticity is governed by the preferential activity of Hippo signaling in the AT1 cell lineage. Thus, cellular plasticity is a temporally acquired trait of the alveolar epithelium and presents an alternative mode of tissue regeneration in the postnatal lung.

Genomic, epigenomic, and biophysical cues controlling the emergence of the lung alveolus.

The lung alveolus is the functional unit of the respiratory system required for gas exchange. During the transition to air breathing at birth, biophysical forces are thought to shape the emerging tissue niche. However, the intercellular signaling that drives these processes remains poorly understood. Applying a multimodal approach, we identified alveolar type 1 (AT1) epithelial cells as a distinct signaling hub. Lineage tracing demonstrates that AT1 progenitors align with receptive, force-exerting myofibroblasts in a spatial and temporal manner. Through single-cell chromatin accessibility and pathway expression (SCAPE) analysis, we demonstrate that AT1-restricted ligands are required for myofibroblasts and alveolar formation. These studies show that the alignment of cell fates, mediated by biophysical and AT1-derived paracrine signals, drives the extensive tissue remodeling required for postnatal respiration.

Effectiveness and tolerability of adjunctive brivaracetam in patients with focal seizures: Second interim analysis of 6-month data from a prospective observational study in Europe.

Brivaracetam (BRV) is indicated for adjunctive treatment of focal (partial-onset) seizures with or without secondary generalisation in patients 4 years of age and older in the European Union (EU). An ongoing 12-month, prospective, non-interventional post-marketing study (EP0077; NCT02687711) is collecting real-world information on patients receiving treatment with adjunctive BRV in Europe. In this study, BRV is prescribed according to routine clinical practice and the EU Summary of Product Characteristics. This second interim analysis assessed effectiveness, tolerability and health-related quality of life outcomes for up to 6 months of treatment. At the cut-off date (13 April 2018), 266 patients from five countries had attended Visit 1, 24.1 % (64/266) had completed the study, 37.6 % (100/266) were ongoing, and 38.3 % (102/266) had discontinued. In total, 261 patients had at least one dose of BRV and were included in the analyses. Patients had a mean time since epilepsy diagnosis of 23.2 years, a mean of eight lifetime AEDs (sum of AEDs discontinued prior to study entry and concomitant at study entry), and a median of five focal seizures per 28 days during the 3-month retrospective Baseline. 66.3 % of patients initiated BRV at a dose within the recommended starting range (50-100 mg/day) and 87.1 % of patients received BRV modal doses within the recommended dose range (50-200 mg/day) during the study. Retention rates were 79.1 % (N = 239) at 3 months and 62.1 % (N = 211) at 6 months. The 50 % responder rates for focal seizures were 46.8 % (N = 139) at 3 months and 53.6 % (N = 97) at 6 months. The proportions of patients who were seizure-free were 10.7 % (21/196) and 7.5 % (15/199) at 3 and 6 months of treatment, respectively. Median percent reductions in focal seizure frequency per 28 days from Baseline to 3 and 6 months were 34.6 % (N = 139) and 53.3 % (N = 97), respectively. Overall, 44.2 % of patients had an improvement and 15.4 % had a worsening in Patient Weighted Quality of Life in Epilepsy Inventory-Form 31 total score from Baseline to 6 months (N = 52). At least one treatment-emergent adverse event (TEAE) was reported in 51.0 % (133/261) of patients, and 34.5 % (90/261) of patients had drug-related TEAEs. The most common drug-related TEAEs (≥5% of patients) were drug ineffective (7.7 %), seizure (6.5 %), and fatigue (6.1 %). In this 6-month interim analysis, BRV showed effectiveness when used in clinical practice in five European countries. BRV was well tolerated, and no new safety signals were observed.

Direct Comparison of Mononucleated and Binucleated Cardiomyocytes Reveals Molecular Mechanisms Underlying Distinct Proliferative Competencies.

The mammalian heart is incapable of regenerating a sufficient number of cardiomyocytes to ameliorate the loss of contractile muscle after acute myocardial injury. Several reports have demonstrated that mononucleated cardiomyocytes are more responsive than are binucleated cardiomyocytes to pro-proliferative stimuli. We have developed a strategy to isolate and characterize highly enriched populations of mononucleated and binucleated cardiomyocytes at various times of development. Our results suggest that an E2f/Rb transcriptional network is central to the divergence of these two populations and that remnants of the differences acquired during the neonatal period remain in adult cardiomyocytes. Moreover, inducing binucleation by genetically blocking the ability of cardiomyocytes to complete cytokinesis leads to a reduction in E2f target gene expression, directly linking the E2f pathway with nucleation. These data identify key molecular differences between mononucleated and binucleated mammalian cardiomyocytes that can be used to leverage cardiomyocyte proliferation for promoting injury repair in the heart.

Defining the role of pulmonary endothelial cell heterogeneity in the response to acute lung injury.

Pulmonary endothelial cells (ECs) are an essential component of the gas exchange machinery of the lung alveolus. Despite this, the extent and function of lung EC heterogeneity remains incompletely understood. Using single-cell analytics, we identify multiple EC populations in the mouse lung, including macrovascular endothelium (maEC), microvascular endothelium (miECs), and a new population we have termed Car4-high ECs. Car4-high ECs express a unique gene signature, and ligand-receptor analysis indicates they are primed to receive reparative signals from alveolar type I cells. After acute lung injury, they are preferentially localized in regenerating regions of the alveolus. Influenza infection reveals the emergence of a population of highly proliferative ECs that likely arise from multiple miEC populations and contribute to alveolar revascularization after injury. These studies map EC heterogeneity in the adult lung and characterize the response of novel EC subpopulations required for tissue regeneration after acute lung injury.

Animal lungs are filled with tiny air sacks called alveoli, where the gas exchanges that keep organisms alive can take place. Small blood vessels known as capillaries come in close contact with the alveoli, allowing oxygen to be extracted from the air into the blood, and carbon dioxide to be released from the blood into the air. The cells that line the inside of these capillaries (known as pulmonary endothelial cells) are important actors in these exchanges. After having been damaged, for example by viruses like influenza, the lungs need to regenerate and create new capillaries. Yet, it was still unclear how pulmonary endothelial cells participate in the healing process, and if capillaries contain several populations of endothelial cells that play different roles. To investigate this question, Niethamer et al. used an approach called single-cell analytics to examine individual endothelial cells in the alveoli of mice infected with influenza. This revealed that different subtypes of endothelial cells exist in capillaries, and that some may be able to perform slightly different jobs during lung recovery. Niethamer et al. found that all subtypes could quickly multiply after injury to create more endothelial cells and re-establish gas exchanges. However, one newly identified group (called Car4-high ECs) was particularly primed to receive orders from damaged alveoli. These cells were also often found at the sites where the alveoli were most injured. Lung injuries are a major cause of death worldwide. Understanding how pulmonary endothelial cells work when the organ is both healthy and injured should help to find ways to boost repair, and to create therapies that could target these cells.

YAP Partially Reprograms Chromatin Accessibility to Directly Induce Adult Cardiogenesis In Vivo.

Specialized adult somatic cells, such as cardiomyocytes (CMs), are highly differentiated with poor renewal capacity, an integral reason underlying organ failure in disease and aging. Among the least renewable cells in the human body, CMs renew approximately 1% annually. Consistent with poor CM turnover, heart failure is the leading cause of death. Here, we show that an active version of the Hippo pathway effector YAP, termed YAP5SA, partially reprograms adult mouse CMs to a more fetal and proliferative state. One week after induction, 19% of CMs that enter S-phase do so twice, CM number increases by 40%, and YAP5SA lineage CMs couple to pre-existing CMs. Genomic studies showed that YAP5SA increases chromatin accessibility and expression of fetal genes, partially reprogramming long-lived somatic cells in vivo to a primitive, fetal-like, and proliferative state.