COVID-19 real-world data for the US and lessons to reopen business.

This Pearl article recounts the story of a US corporation, Lennar, the nation's leading homebuilder, an essential function in the US (not allowed to lock down), when faced with the coronavirus disease 2019 (COVID-19) pandemic at the end of February 2020. The culture of the company, which allowed it to proceed safely, is one of cohesion, trust, teamwork, and respect for fellow humans. Theirs is a culture in which the safety, wellness, and health of the associates (employees) and the communities they serve is the number one priority. All associates wear a name badge with first name only, and all name badges share the same family name, Lennar. At Lennar, individual success means nothing, and collective success means everything. This is the story of how Lennar took control of the COVID-19 pandemic, metamorphosed itself into an even stronger organization, better suited to deal with COVID-19, and more importantly, optimally suited for the 21st century. The lessons learned not only were instrumental to Lennar but could also apply to any company eager to reopen their business.

Evaluation of exosome derivatives as bio-informational reprogramming therapy for cancer.

Exosomes are nanoparticle sized (100 ± 50 nm) extracellular vesicles (ECVs) that play important roles in cell-to-cell communication. They do this by utilizing their natural ability to shuttle signaling molecules across the cellular microenvironment and promote paracrine signaling. Currently, exosomes are being explored for their potential as therapeutic agents for various degenerative diseases including cancer. The rationale behind their therapeutic ability is that they can transfer signaling biomolecules, and subsequently induce metabolic and physiological changes in diseased cells and tissues. In addition, exosomes can be used as a drug delivery system and may be very effective at reducing toxicity and increasing bioavailability of therapeutic molecules and drugs. Although exosomes were first believed to be a waste product of the cell, current research has demonstrated that these particles can serve as modulators of the immune system, act as cancer biomarkers, cause re-differentiation of cancer cells, and induce apoptosis in diseased cells. Extensive research has been performed specifically using amniotic fluid-derived extracellular vesicles, named "cytosomes". While the use of cytosomes in clinical application is still in the early stages, researchers have shown great potential for these EVs in regenerative medicine as immune modulators, in controlling microbial infection and by inducing tissue repair through the activation of endogenous, tissue-specific stem cells. This review emphasizes the capabilities of specific subsets of extracellular vesicles that can potentially be used for cancer therapy, principally as a source of bi-informational reprogramming for malignant cells.

PDGFRA defines the mesenchymal stem cell Kaposi's sarcoma progenitors by enabling KSHV oncogenesis in an angiogenic environment.

Kaposi's sarcoma (KS) is an AIDS-defining cancer caused by the KS-associated herpesvirus (KSHV). Unanswered questions regarding KS are its cellular ontology and the conditions conducive to viral oncogenesis. We identify PDGFRA(+)/SCA-1(+) bone marrow-derived mesenchymal stem cells (Pα(+)S MSCs) as KS spindle-cell progenitors and found that pro-angiogenic environmental conditions typical of KS are critical for KSHV sarcomagenesis. This is because growth in KS-like conditions generates a de-repressed KSHV epigenome allowing oncogenic KSHV gene expression in infected Pα(+)S MSCs. Furthermore, these growth conditions allow KSHV-infected Pα(+)S MSCs to overcome KSHV-driven oncogene-induced senescence and cell cycle arrest via a PDGFRA-signaling mechanism; thus identifying PDGFRA not only as a phenotypic determinant for KS-progenitors but also as a critical enabler for viral oncogenesis.

KSHV-induced ligand mediated activation of PDGF receptor-alpha drives Kaposi's sarcomagenesis.

Kaposi's sarcoma (KS) herpesvirus (KSHV) causes KS, an angiogenic AIDS-associated spindle-cell neoplasm, by activating host oncogenic signaling cascades through autocrine and paracrine mechanisms. Tyrosine kinase receptor (RTK) proteomic arrays, identified PDGF receptor-alpha (PDGFRA) as the predominantly-activated RTK in KSHV-induced mouse KS-tumors. We show that: 1) KSHV lytic replication and the vGPCR can activate PDGFRA through upregulation of its ligands PDGFA/B, which increase c-myc, VEGF and KSHV gene expression in infected cells 2) KSHV infected spindle cells of most AIDS-KS lesions display robust phospho-PDGFRA staining 3) blocking PDGFRA-signaling with N-acetyl-cysteine, RTK-inhibitors Imatinib and Sunitinib, or dominant-negative PDGFRA inhibits tumorigenesis 4) PDGFRA D842V activating-mutation confers resistance to Imatinib in mouse-KS tumorigenesis. Our data show that KSHV usurps sarcomagenic PDGFRA signaling to drive KS. This and the fact that PDGFRA drives non-viral sarcomas highlights the importance for KSHV-induced ligand-mediated activation of PDGFRA in KS sarcomagenesis and shows that this oncogenic axis could be successfully blocked to impede KS tumor growth.

Accelerated coronary atherosclerosis not explained by traditional risk factors in 13% of young individuals.

IMPORTANCE: Most individuals who die of sudden cardiac death (SCD) display very advanced lesions of atherosclerosis in their coronary arteries. Thus, we sought to identify and characterize a putative subpopulation of young individuals exhibiting accelerated coronary artery atherosclerosis. OBJECTIVE: Our analysis of the Pathobiological Determinants of Atherosclerosis in Youth (PDAY) study-which examined 2651 individuals, obtaining quantitative measurements of traditional risk factors for coronary heart disease (CHD)-aimed to identify individuals with advanced coronary artery lesions, and to determine whether risk factors could account for such rapid disease progression, or not. DESIGN: Using the cross-sectional PDAY study data, an exploratory de facto analysis stratified the population by age and observed number of coronary raised lesions and examined these groups via Poisson regression modeling. A separate de novo approach utilized Poisson mixture modeling to generate low- and high-growth groups based on measurements of traditional risk factors, and identified factors contributing to disease progression. PARTICIPANTS: Participants, n = 2651 individuals aged 15-34, who had died of non-cardiac death, were recruited post mortem. Tissues and other samples were harvested for analysis (details in previously published PDAY studies). Main Outcome(s) and Measure(s). Using quantitative measurements of raised coronary lesions and traditional risk factors of CHD, we sought to identify which risk factors account for disease progression. RESULTS: A group of ~13% of the PDAY population exhibits accelerated coronary atherosclerosis despite their young age. Several traditional risk factors were associated with increased odds of inclusion in this subgroup, reflecting current understanding of these markers of disease. However, only age was a significant contributing factor to the observed coronary lesion burden. CONCLUSIONS: While a range of traditional risk factors contribute to an individual's inclusion to the identified subgroup with accelerated atherosclerosis, these factors, with the exceptions of age, are not able to predict an individual's lesion burden. Moreover, unattributed variances in observations indicate the need to study novel risk factors. SHORT SUMMARY: Hypothesis The extent of coronary atherosclerotic disease is limited and homogeneous within youth, and its progression can be accounted for by traditional risk factors in this population. FINDINGS: A subpopulation (~13%) of the Pathobiological Determinants of Atherosclerosis in Youth cohort exhibited accelerated coronary artery atherosclerosis. While several traditional risk factors contribute to an individual's inclusion in this subgroup, these factors, with the exceptions of age, do not predict accurately an individual's lesions burden. Critically, unattributed variances in observations indicate the need for the identification of novel risk factors. MEANING: Screening of the general population at a young age for high-risk group membership could provide opportunity for disease prevention and avoidance of the worse complications such as myocardial infarction and sudden cardiac death later in life.

Epigenetic regulation of COL15A1 in smooth muscle cell replicative aging and atherosclerosis.

Smooth muscle cell (SMC) proliferation is a hallmark of vascular injury and disease. Global hypomethylation occurs during SMC proliferation in culture and in vivo during neointimal formation. Regardless of the programmed or stochastic nature of hypomethylation, identifying these changes is important in understanding vascular disease, as maintenance of a cells' epigenetic profile is essential for maintaining cellular phenotype. Global hypomethylation of proliferating aortic SMCs and concomitant decrease of DNMT1 expression were identified in culture during passage. An epigenome screen identified regions of the genome that were hypomethylated during proliferation and a region containing Collagen, type XV, alpha 1 (COL15A1) was selected by 'genomic convergence' for characterization. COL15A1 transcript and protein levels increased with passage-dependent decreases in DNA methylation and the transcript was sensitive to treatment with 5-Aza-2'-deoxycytidine, suggesting DNA methylation-mediated gene expression. Phenotypically, knockdown of COL15A1 increased SMC migration and decreased proliferation and Col15a1 expression was induced in an atherosclerotic lesion and localized to the atherosclerotic cap. A sequence variant in COL15A1 that is significantly associated with atherosclerosis (rs4142986, P = 0.017, OR = 1.434) was methylated and methylation of the risk allele correlated with decreased gene expression and increased atherosclerosis in human aorta. In summary, hypomethylation of COL15A1 occurs during SMC proliferation and the consequent increased gene expression may impact SMC phenotype and atherosclerosis formation. Hypomethylated genes, such as COL15A1, provide evidence for concomitant epigenetic regulation and genetic susceptibility, and define a class of causal targets that sit at the intersection of genetic and epigenetic predisposition in the etiology of complex disease.

MicroRNA-10A* and MicroRNA-21 modulate endothelial progenitor cell senescence via suppressing high-mobility group A2.

RATIONALE: Endothelial progenitor cells (EPCs) contribute to the regeneration of endothelium. Aging-associated senescence results in reduced number and function of EPCs, potentially contributing to increased cardiac risk, reduced angiogenic capacity, and impaired cardiac repair effectiveness. The mechanisms underlying EPC senescence are unknown. Increasing evidence supports the role of microRNAs in regulating cellular senescence. OBJECTIVE: We aimed to determine whether microRNAs regulated EPC senescence and, if so, what the underlying mechanisms are. METHODS AND RESULTS: To map the microRNA/gene expression signatures of EPC senescence, we performed microRNA profiling and microarray analysis in lineage-negative bone marrow cells from young and aged wild-type and apolipoprotein E-deficient mice. We identified 2 microRNAs, microRNA-10A* (miR-10A*), and miR-21, and their common target gene Hmga2 as critical regulators for EPC senescence. Overexpression of miR-10A* and miR-21 in young EPCs suppressed Hmga2 expression, caused EPC senescence, as evidenced by senescence-associated ß-galactosidase upregulation, decreased self-renewal potential, increased p16(Ink4a)/p19(Arf) expression, and resulted in impaired EPC angiogenesis in vitro and in vivo, resembling EPCs derived from aged mice. In contrast, suppression of miR-10A* and miR-21 in aged EPCs increased Hmga2 expression, rejuvenated EPCs, resulting in decreased senescence-associated ß-galactosidase expression, increased self-renewal potential, decreased p16(Ink4a)/p19(Arf) expression, and improved EPC angiogenesis in vitro and in vivo. Importantly, these phenotypic changes were rescued by miRNA-resistant Hmga2 cDNA overexpression. CONCLUSIONS: miR-10A* and miR-21 regulate EPC senescence via suppressing Hmga2 expression and modulation of microRNAs may represent a potential therapeutic intervention in improving EPC-mediated angiogenesis and vascular repair.

Genomic signatures of a global fitness index in a multi-ethnic cohort of women.

The rates of obesity and sedentary lifestyle are on a dramatic incline, with associated detrimental health effects among women in particular. Although exercise prescriptions are useful for overcoming these problems, success can be hampered by differential responsiveness among individuals in cardiovascular fitness indices (i.e. improvements in strength, lipids, VO(2) max). Genomic factors appear to play an important role in determining this inter-individual variation. We performed microarray analyses on mRNA in whole blood from 60 sedentary women from a multi-ethnic cohort who underwent 12 weeks of exercise, to identify gene subsets that were differentially expressed between individuals who experienced the greatest and least improvements in fitness. We identified 43 transcripts in 39 unique genes (FDR<10%; FC>1.5) whose expression increased the most in "high" versus "low" pre-menopausal female responders. These 39 genes were enriched in six biological pathways, including oxidative phosphorylation (p = 8.08 × 10(-3)). Several of the 39 genes (i.e. TIGD7, UQCRH, PSMA6, WDR12, TFB2M, USP15) have previously reported associations with fitness-related phenotypes. In summary, we identified gene signatures based on mRNA analysis that define responsiveness to exercise in a largely minority-based female cohort. Importantly, this study validates several genes/pathways previously associated with exercise responsiveness and extends these findings with additional novel genes.

First Case of Accelerated Healing of a Recalcitrant Diabetic Ulcer Using Purified Amniotic Fluid.

We report the first case of recalcitrant diabetic wound treated successfully by twice-daily applications of a sterile fraction of human purified amniotic fluid (ViX001) obtained from thoroughly screened volunteers at the time of planned c-section at the term of normal pregnancies. Our product ViX001 was generated through a proprietary process and kept in frozen one milliliter (1 ml) vials (protein content was ~1mg/ml) thawed prior to applications (shelf life at 34oF of at least two weeks).

First Case of Severe Pain and Inflammation Reduction by Application of Purified Amniotic Fluid on Active Lesions of a Patient with Pyoderma Gangrenosum.

We report the first case of severe pain and inflammation reduction by application of purified amniotic fluid on active lesions of a patient with pyoderma gangrenosum. We describe the impact of every third-day skin applications of a sterile fraction (4ml) from human purified amniotic fluid (ViX001) obtained from thoroughly screened volunteers at the time of planned c-section at the term of normal pregnancies. The product ViX001 was generated through a proprietary process and kept in frozen one or two milliliters cryovials (protein content was ~1mg/ml) and thawed just prior to applications. Pain improvement was recorded after each application, and inflammation suppression was confirmed by serial pictures of the lesions. While our findings need to be reproduced with a larger cohort of patients, preferably at an earlier stage of the disease, it is instructive that ViX001 reduced severe pain and inflammation for a patient with advanced pyoderma gangrenosum. Pyoderma gangrenosum is a dreadful skin condition consisting of noninfectious neutrophilic dermatosis that progresses to necrotic ulcers with a characteristic purple edge and extremely painful raw subdermal tissue exposure.

First Case of Debilitating Lower Back Pain Induced by Severe Inflammation of Lumbar Joints, Healed by Intravenous Infusions of Purified Amniotic Fluid.

We report the first case of debilitating lower back pain induced by spondylitis with end plate inflammation of the lumbar spine, treated successfully by bi-weekly intravenous injections of a sterile fraction (1ml) from human purified amniotic fluid (ViX001) obtained from thoroughly screened volunteers at the time of planned c-section at the term of normal pregnancies. Our product ViX001 was generated through a proprietary process and kept in frozen one milliliter (1 ml) cryvials (protein content was ~1mg/ml) and thawed just prior to injections. Pain improvement was recorded weekly, and inflammation suppression was confirmed by monthly MRIs of the lumbar spine. While our findings need to be reproduced with a larger cohort of patients, it is instructive that ViX001 resolved pain and inflammation for a patient with severe lower back pain, the most common form of pain reported by U.S. adults.

Atherosclerosis, inflammation, genetics, and stem cells: 2012 update.

Atherosclerosis is a peculiar form of inflammation triggered by cholesterol-rich lipoproteins and other noxious factors such as cigarette smoke, diabetes mellitus, and hypertension. Genetics also play an important role in the disease, accounting for about 40% of the risk. Of surprise in recent years of post-human genome sequencing, atherosclerosis-relevant genes discovered by non-biased techniques (ie, genome-wide association studies), did not rehash previously suspected pathways of lipid metabolism, diabetes, or hypertension. Instead these studies highlighted genes relevant to mechanisms of inflammation and stem cell biology. Only a minority of implicated genes were linked to lipid and other cardiac risk factor genes. Although such findings do not contradict the fact that atherosclerosis is triggered and exacerbated by elevated lipids, atherosclerosis "new genes" suggest that the mechanism responsible for the development of arterial lesions is more complex than a simple response to injury, where injury is necessary, but perhaps not sufficient, for disease progression.

Antitumorigenesis of antioxidants in a transgenic Rac1 model of Kaposi's sarcoma.

Kaposi's sarcoma (KS) is the major AIDS-associated malignancy. It is characterized by the proliferation of spindle cells, inflammatory infiltrate, and aberrant angiogenesis caused by Kaposi's sarcoma herpesvirus (KSHV) infection. Small GTPase Rac1, an inflammatory signaling mediator triggering reactive oxygen species (ROS) production by NADPH-oxidases, is implicated in carcinogenesis and tumor angiogenesis. Here, we show that expression of a constitutively active Rac1 (RacCA) driven by the alpha-smooth muscle actin promoter in transgenic mice is sufficient to cause KS-like tumors through mechanisms involving ROS-driven proliferation, up-regulation of AKT signaling, and hypoxia-inducible factor 1-alpha-related angiogenesis. RacCA-induced tumors expressed KS phenotypic markers; displayed remarkable transcriptome overlap with KS lesions; and were, like KS, associated with male gender. The ROS scavenging agent N-acetyl-cysteine inhibited angiogenesis and completely abrogated transgenic RacCA tumor formation, indicating a causal role of ROS in tumorigenesis. Consistent with a pathogenic role in KS, immunohistochemical analysis revealed that Rac1 is overexpressed in KSHV(+) spindle cells of AIDS-KS biopsies. Our results demonstrate the direct oncogenicity of Rac1 and ROS and their contribution to a KS-like malignant phenotype, further underscoring the carcinogenic potential of oxidative stress in the context of chronic infection and inflammation. They define the RacCA transgenic mouse as a model suitable for studying the role of oxidative stress in the pathogenesis and therapy of KS, with relevance to other inflammation-related malignancies. Our findings suggest host and viral genes triggering Rac1 or ROS production as key determinants of KS onset and potential KS chemopreventive or therapeutic targets.

Neuropeptide Y gene polymorphisms confer risk of early-onset atherosclerosis.

Neuropeptide Y (NPY) is a strong candidate gene for coronary artery disease (CAD). We have previously identified genetic linkage to familial CAD in the genomic region of NPY. We performed follow-up genetic, biostatistical, and functional analysis of NPY in early-onset CAD. In familial CAD (GENECARD, N = 420 families), we found increased microsatellite linkage to chromosome 7p14 (OSA LOD = 4.2, p = 0.004) in 97 earliest age-of-onset families. Tagged NPY SNPs demonstrated linkage to CAD of a 6-SNP block (LOD = 1.58-2.72), family-based association of this block with CAD (p = 0.02), and stronger linkage to CAD in the earliest age-of-onset families. Association of this 6-SNP block with CAD was validated in: (a) 556 non-familial early-onset CAD cases and 256 controls (OR 1.46-1.65, p = 0.01-0.05), showing stronger association in youngest cases (OR 1.84-2.20, p = 0.0004-0.09); and (b) GENECARD probands versus non-familial controls (OR 1.79-2.06, p = 0.003-0.02). A promoter SNP (rs16147) within this 6-SNP block was associated with higher plasma NPY levels (p = 0.04). To assess a causal role of NPY in atherosclerosis, we applied the NPY1-receptor-antagonist BIBP-3226 adventitially to endothelium-denuded carotid arteries of apolipoprotein E-deficient mice; treatment reduced atherosclerotic neointimal area by 50% (p = 0.03). Thus, NPY variants associate with atherosclerosis in two independent datasets (with strong age-of-onset effects) and show allele-specific expression with NPY levels, while NPY receptor antagonism reduces atherosclerosis in mice. We conclude that NPY contributes to atherosclerosis pathogenesis.

Rivalry between Humans and Coronaviruses: Unanticipated Impact of Omicron.

With our prior Commentary we discussed the rivalry between ideation (humans) and mutations (viruses), (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8439168/), and more specifically, we described and compared two means of adaptability: collective and focused ideation for humans and self-serving mutation for viruses. The amazingly fast development of new effective and safe vaccines and drugs requires the humankind's most sophisticated form of ideation ability to respond to threatening stressors such as a dangerous virus like SARS-CoV-2. The essence of what makes us human is that human ideation requires a society of people working towards the same goal and is interdependent on socialization for the sustainability of humankind. In contrast, viruses mutate alone and "selfishly". The best fit virus for a particular environment, for a particular host, eliminates the competition through successive mutations. The Omicron variant of concern (VoC) is a great example for how higher transmissibility and perhaps, stochasticity, can drive the transmissive success of a virus across an entire host species like humans. With this review, we describe how Omicron has impacted the COVID-19 pandemic in an unanticipated way that could bring an end to it.

Polymorphic variants in tenascin-C (TNC) are associated with atherosclerosis and coronary artery disease.

Tenascin-C (TNC) is an extracellular matrix protein implicated in biological processes important for atherosclerotic plaque development and progression, including smooth muscle cell migration and proliferation. Previously, we observed differential expression of TNC in atherosclerotic aortas compared with healthy aortas. The goal of this study was to investigate whether common genetic variation within TNC is associated with risk of atherosclerosis and coronary artery disease (CAD) in three independent datasets. We genotyped 35 single nucleotide polymorphisms (SNPs), including 21 haplotype tagging SNPs, in two of these datasets: human aorta tissue samples (n = 205) and the CATHGEN cardiovascular study (n = 1,325). Eleven of these 35 SNPs were then genotyped in a third dataset, the GENECARD family study of early-onset CAD (n = 879 families). Three SNPs representing a block of linkage disequilibrium, rs3789875, rs12347433, and rs4552883, were significantly associated with atherosclerosis in multiple datasets and demonstrated consistent, but suggestive, genetic effects in all analyses. In combined analysis rs3789875 and rs12347433 were statistically significant after Bonferroni correction for 35 comparisons, p = 2 × 10(-6) and 5 × 10(-6), respectively. The SNP rs12347433 is a synonymous coding SNP and may be biologically relevant to the mechanism by which tenascin-C influences the pathophysiology of CAD and atherosclerosis. This is the first report of genetic association between polymorphisms in TNC and atherosclerosis or CAD.

Endothelial progenitor cells (EPCs) mobilized and activated by neurotrophic factors may contribute to pathologic neovascularization in diabetic retinopathy.

Diabetic retinopathy is characterized by pathological retinal neovascularization. Accumulating evidence has indicated that high levels of circulating endothelial progenitor cells (EPCs) are an important risk factor for neovascularization. Paradoxically, the reduction and dysfunction of circulating EPCs has been extensively reported in diabetic patients. We hypothesized that EPCs are differentially altered in the various vasculopathic complications of diabetes mellitus, exhibiting distinct behaviors in terms of angiogenic response to ischemia and growth factors and potentially playing a potent role in motivating vascular precursors to induce pathological neovascularization. Circulating levels of EPCs from diabetic retinopathy patients were analyzed by flow cytometry and by counting EPC colony-forming units, and serum levels of neurotrophic factors were measured by enzyme-linked immunosorbent assay. We found increased levels of nerve growth factor and brain-derived neurotrophic factor in the blood of diabetic retinopathy patients; this increase was correlated with the levels of circulating EPCs. In addition, we demonstrated that retinal cells released neurotrophic factors under hypoxic conditions to enhance EPC activity in vitro and to increase angiogenesis in a mouse ischemic hindlimb model. These results suggest that neurotrophic factors may induce neoangiogenesis through EPC activation, leading to the pathological retinal neovascularization. Thus, we propose that neovascularization in the ischemic retina might be regulated by overexpression of neurotrophic factors.

Origin of neointimal cells in arteriovenous fistulae: bone marrow, artery, or the vein itself?

To elucidate the source of neointimal cells, experimental fistulas were created in Lewis wild-type (WT) and transgenic rats that constitutively expressed the green fluorescent protein (GFP) in all tissues. Arteriovenous fistula (AVFs) were created by anastomosing the left renal vein to the abdominal aorta. The contribution of bone marrow (BM)-derived cells to the AVF neointima was examined in lethally irradiated WT rats that had been rescued with GFP BM cells. Neointimal cells in these chimeric rats were mostly GFP negative indicating the non-BM origin of those cells. Then, the contribution of arterial cells to the AVF neointima was assessed in a fistula made with a GFP aorta that had been implanted orthotopically into a WT rat. Most of the neointimal cells were also GFP negative demonstrating that AVF neointimal cells are not derived from the feeding artery. Finally to study local resident cells contribution to the formation of neointimal lesions, a composite fistula was created by interposing a GFP vein between the renal vein and the aorta in a WT recipient rat. GFP neointimal cells were only found in the transplanted vein. This study suggests that neointimal cells originate from the local resident cells in the venous limb of the fistula.

Rivalry between human ideation and virus mutation: two competing means of sustainability.

For the first time in human history, obtaining a COVID-19 vaccine has become essential for the sustainability of our species. As an amazing product of collective ideation, remarkably safe and efficient vaccines have been invented, tested, distributed, and administered to the population on a voluntary basis. The fast-mutating individual behavior of the virus is probably guided by a similar goal of the sustainability of the species. With this commentary, we analyze and compare two means of sustainability through adaptability: collective ideation in the case of humans and individual mutations in the case of viruses - two very different species whose behaviors are driven by sustainability.

Pregnancy, a unique case of heterochronic parabiosis and peripartum cardiomyopathy.

Introduction: A loss of endogenous stem cells capable of tissue repair and regeneration drives the biological process that we recognize as "aging". Recovery of stem cell-mediated repair and regenerative functions in aged animals has been reported in murine heterochronic parabiosis experiments. Objectives: Herein we will review how pregnancy is an unusual form of heterochronic parabiosis, as the placenta prevents the exchange of most blood cells between parabionts. Instead, plasma and its content, including small extracellular vesicles, can readily cross the placental barrier. These nanosized extracellular vesicles are readily produced by the placenta, amnion, fetus and mother, and are essential for fetal organogenesis, growth and the progression of a healthy pregnancy. If defective, these extracellular vesicles can cause havoc such as in the case of peripartum cardiomyopathy. We will also review how these extracellular vesicles impact the mother substantially (including cardiac function) in the parabiosis of pregnancy. Conclusion: Extracellular vesicles generated during the course of a healthy pregnancy are essential for organogenesis and fetal growth, and also for maternal tissue repair and regeneration, and might be defective or deficient in pregnancies that result in peripartum cardiomyopathy.