Combined Treatment of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes and Endothelial Cells Regenerate the Infarcted Heart in Mice and Non-Human Primates.

BACKGROUND: Remuscularization of the mammalian heart can be achieved after cell transplantation of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs). However, several hurdles remain before implementation into clinical practice. Poor survival of the implanted cells is related to insufficient vascularization, and the potential for fatal arrhythmogenesis is associated with the fetal cell-like nature of immature CMs. METHODS: We generated 3 lines of hiPSC-derived endothelial cells (ECs) and hiPSC-CMs from 3 independent donors and tested hiPSC-CM sarcomeric length, gap junction protein, and calcium-handling ability in coculture with ECs. Next, we examined the therapeutic effect of the cotransplantation of hiPSC-ECs and hiPSC-CMs in nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice undergoing myocardial infarction (n≥4). Cardiac function was assessed by echocardiography, whereas arrhythmic events were recorded using 3-lead ECGs. We further used healthy non-human primates (n=4) with cell injection to study the cell engraftment, maturation, and integration of transplanted hiPSC-CMs, alone or along with hiPSC-ECs, by histological analysis. Last, we tested the cell therapy in ischemic reperfusion injury in non-human primates (n=4, 3, and 4 for EC+CM, CM, and control, respectively). Cardiac function was evaluated by echocardiography and cardiac MRI, whereas arrhythmic events were monitored by telemetric ECG recorders. Cell engraftment, angiogenesis, and host-graft integration of human grafts were also investigated. RESULTS: We demonstrated that human iPSC-ECs promote the maturity and function of hiPSC-CMs in vitro and in vivo. When cocultured with ECs, CMs showed more mature phenotypes in cellular structure and function. In the mouse model, cotransplantation augmented the EC-accompanied vascularization in the grafts, promoted the maturity of CMs at the infarct area, and improved cardiac function after myocardial infarction. Furthermore, in non-human primates, transplantation of ECs and CMs significantly enhanced graft size and vasculature and improved cardiac function after ischemic reperfusion. CONCLUSIONS: These results demonstrate the synergistic effect of combining iPSC-derived ECs and CMs for therapy in the postmyocardial infarction heart, enabling a promising strategy toward clinical translation.

Metabolic Changes Associated With Cardiomyocyte Dedifferentiation Enable Adult Mammalian Cardiac Regeneration.

BACKGROUND: Cardiac regeneration after injury is limited by the low proliferative capacity of adult mammalian cardiomyocytes (CMs). However, certain animals readily regenerate lost myocardium through a process involving dedifferentiation, which unlocks their proliferative capacities. METHODS: We bred mice with inducible, CM-specific expression of the Yamanaka factors, enabling adult CM reprogramming and dedifferentiation in vivo. RESULTS: Two days after induction, adult CMs presented a dedifferentiated phenotype and increased proliferation in vivo. Microarray analysis revealed that upregulation of ketogenesis was central to this process. Adeno-associated virus-driven HMGCS2 overexpression induced ketogenesis in adult CMs and recapitulated CM dedifferentiation and proliferation observed during partial reprogramming. This same phenomenon was found to occur after myocardial infarction, specifically in the border zone tissue, and HMGCS2 knockout mice showed impaired cardiac function and response to injury. Finally, we showed that exogenous HMGCS2 rescues cardiac function after ischemic injury. CONCLUSIONS: Our data demonstrate the importance of HMGCS2-induced ketogenesis as a means to regulate metabolic response to CM injury, thus allowing cell dedifferentiation and proliferation as a regenerative response.

Loss of Gut Microbiota Alters Immune System Composition and Cripples Postinfarction Cardiac Repair.

BACKGROUND: The impact of gut microbiota on the regulation of host physiology has recently garnered considerable attention, particularly in key areas such as the immune system and metabolism. These areas are also crucial for the pathophysiology of and repair after myocardial infarction (MI). However, the role of the gut microbiota in the context of MI remains to be fully elucidated. METHODS: To investigate the effects of gut microbiota on cardiac repair after MI, C57BL/6J mice were treated with antibiotics 7 days before MI to deplete mouse gut microbiota. Flow cytometry was applied to examine the changes in immune cell composition in the heart. 16S rDNA sequencing was conducted as a readout for changes in gut microbial composition. Short-chain fatty acid (SCFA) species altered after antibiotic treatment were identified by high-performance liquid chromatography. Fecal reconstitution, transplantation of monocytes, or dietary SCFA or Lactobacillus probiotic supplementation was conducted to evaluate the cardioprotective effects of microbiota on the mice after MI. RESULTS: Antibiotic-treated mice displayed drastic, dose-dependent mortality after MI. We observed an association between the gut microbiota depletion and significant reductions in the proportion of myeloid cells and SCFAs, more specifically acetate, butyrate, and propionate. Infiltration of CX3CR1+ monocytes to the peri-infarct zone after MI was also reduced, suggesting impairment of repair after MI. Accordingly, the physiological status and survival of mice were significantly improved after fecal reconstitution, transplantation of monocytes, or dietary SCFA supplementation. MI was associated with a reorganization of the gut microbial community such as a reduction in Lactobacillus. Supplementing antibiotic-treated mice with a Lactobacillus probiotic before MI restored myeloid cell proportions, yielded cardioprotective effects, and shifted the balance of SCFAs toward propionate. CONCLUSIONS: Gut microbiota-derived SCFAs play an important role in maintaining host immune composition and repair capacity after MI. This suggests that manipulation of these elements may provide opportunities to modulate pathological outcome after MI and indeed human health and disease as a whole.

Copy number variant hotspots in Han Taiwanese population induced pluripotent stem cell lines - lessons from establishing the Taiwan human disease iPSC Consortium Bank.

BACKGROUND: The Taiwan Human Disease iPSC Service Consortium was established to accelerate Taiwan's growing stem cell research initiatives and provide a platform for researchers interested in utilizing induced pluripotent stem cell (iPSC) technology. The consortium has generated and characterized 83 iPSC lines: 11 normal and 72 disease iPSC lines covering 21 different diseases, several of which are of high incidence in Taiwan. Whether there are any reprogramming-induced recurrent copy number variant (CNV) hotspots in iPSCs is still largely unknown. METHODS: We performed genome-wide copy number variant screening of 83 Han Taiwanese iPSC lines and compared them with 1093 control subjects using an Affymetrix genome-wide human SNP array. RESULTS: In the iPSCs, we identified ten specific CNV loci and seven "polymorphic" CNV regions that are associated with the reprogramming process. Additionally, we established several differentiation protocols for our iPSC lines. We demonstrated that our iPSC-derived cardiomyocytes respond to pharmacological agents and were successfully engrafted into the mouse myocardium demonstrating their potential application in cell therapy. CONCLUSIONS: The CNV hotspots induced by cell reprogramming have successfully been identified in the current study. This finding may be used as a reference index for evaluating iPSC quality for future clinical applications. Our aim was to establish a national iPSC resource center generating iPSCs, made available to researchers, to benefit the stem cell community in Taiwan and throughout the world.

Human iPSC banking: barriers and opportunities.

The introduction of induced pluripotent stem cells (iPSCs) has opened up the potential for personalized cell therapies and ushered in new opportunities for regenerative medicine, disease modeling, iPSC-based drug discovery and toxicity assessment. Over the past 10 years, several initiatives have been established that aim to collect and generate a large amount of human iPSCs for scientific research purposes. In this review, we compare the construction and operation strategy of some iPSC banks as well as their ongoing development. We also introduce the technical challenges and offer future perspectives pertaining to the establishment and management of iPSC banks.

Mechanisms of pluripotency maintenance in mouse embryonic stem cells.

Mouse embryonic stem cells (mESCs), characterized by their pluripotency and capacity for self-renewal, are driven by a complex gene expression program composed of several regulatory mechanisms. These mechanisms collaborate to maintain the delicate balance of pluripotency gene expression and their disruption leads to loss of pluripotency. In this review, we provide an extensive overview of the key pillars of mESC pluripotency by elaborating on the various essential transcription factor networks and signaling pathways that directly or indirectly support this state. Furthermore, we consider the latest developments in the role of epigenetic regulation, such as noncoding RNA signaling or histone modifications.

Harnessing the early post-injury inflammatory responses for cardiac regeneration.

Cardiac inflammation is considered by many as the main driving force in prolonging the pathological condition in the heart after myocardial infarction. Immediately after cardiac ischemic injury, neutrophils are the first innate immune cells recruited to the ischemic myocardium within the first 24 h. Once they have infiltrated the injured myocardium, neutrophils would then secret proteases that promote cardiac remodeling and chemokines that enhance the recruitment of monocytes from the spleen, in which the recruitment peaks at 72 h after myocardial infarction. Monocytes would transdifferentiate into macrophages after transmigrating into the infarct area. Both neutrophils and monocytes-derived macrophages are known to release proteases and cytokines that are detrimental to the surviving cardiomyocytes. Paradoxically, these inflammatory cells also play critical roles in repairing the injured myocardium. Depletion of either neutrophils or monocytes do not improve overall cardiac function after myocardial infarction. Instead, the left ventricular function is further impaired and cardiac fibrosis persists. Moreover, the inflammatory microenvironment created by the infiltrated neutrophils and monocytes-derived macrophages is essential for the recruitment of cardiac progenitor cells. Recent studies also suggest that treatment with anti-inflammatory drugs may cause cardiac dysfunction after injury. Indeed, clinical studies have shown that traditional ant-inflammatory strategies are ineffective to improve cardiac function after infarction. Thus, the focus should be on how to harness these inflammatory events to either improve the efficacy of the delivered drugs or to favor the recruitment of cardiac progenitor cells.

Circulating cells contribute to cardiomyocyte regeneration after injury.

RATIONALE: The contribution of bone marrow-borne hematopoietic cells to the ischemic myocardium has been documented. However, a pivotal study reported no evidence of myocardial regeneration from hematopoietic-derived cells. The study did not take into account the possible effect of early injury-induced signaling as the test mice were parabiotically paired to partners immediately after surgery-induced myocardial injury when cross-circulation has not yet developed. OBJECTIVE: To re-evaluate the role of circulating cells in the injured myocardium. METHODS AND RESULTS: By combining pulse-chase labeling and parabiosis model, we show that circulating cells derived from the parabiont expressed cardiac-specific markers in the injured myocardium. Genetic fate mapping also revealed that circulating hematopoietic cells acquired cardiac cell fate by means of cell fusion and transdifferentiation. CONCLUSIONS: These results suggest that circulating cells participate in cardiomyocyte regeneration in a mouse model of parabiosis when the circulatory system is fully developed before surgery-induced heart injury.

Concomitant beige adipocyte differentiation upon induction of mesenchymal stem cells into brown adipocytes.

The accumulation of fat, which results in obesity, is related to many metabolic disorders. Besides white and brown adipose tissue, beige adipose tissue has recently been recognized as a new type of accumulated fat. Mesenchymal stem cells (MSCs) have been shown to differentiate into brown adipocytes. Through analyzing levels of mRNA and protein markers associated with beige adipocyte, we found concomitant beige adipocyte differentiation upon induction of MSCs into brown adipocytes in a defined medium containing triiodothyronine, insulin, dexamethasone, and indomethacin. Moreover, we found that protein kinase A (PKA) modulators regulated MSC differentiation into brown or beige adipocytes. Activation of PKA by isobutylmethylxanthine or forskolin increased brown adipocyte differentiation and reduced beige adipocyte differentiation, while inactivation of PKA by KT-5720 or SC-3010 or the knockdown of PKA downstream cAMP response element-binding protein (CREB) decreased brown adipocyte differentiation and increased beige adipocyte differentiation. We also showed that increased brown adipocyte differentiation was accompanied by an increase in mitochondrial mass. In conclusion, we propose a model of beige/brown co-differentiation in MSCs and develop a method for controlling this differentiation via PKA modulation.

Bcl3 Bridges LIF-STAT3 to Oct4 Signaling in the Maintenance of Naïve Pluripotency.

Leukemia inhibitory factor (LIF) regulates mouse embryonic stem cell (mESC) pluripotency through STAT3 activation, but the downstream signaling remains largely unelucidated. Using cDNA microarrays, we verified B cell leukemia/lymphoma 3 (Bcl3) as the most significantly downregulated factor following LIF withdrawal in mESCs. Bcl3 knockdown altered mESC morphology, reduced expression of pluripotency genes including Oct4, Sox2, and Nanog, and downregulated DNA binding of acetylated histone 3 and RNA polymerase II on the Oct4 promoter. Conversely, Bcl3 overexpression partially prevented cell differentiation and promoted Oct4 and Nanog promoter activities. Furthermore, coimmunoprecipitation and chromatin immunoprecipitation experiments demonstrated that Bcl3 regulation of mESC pluripotency may be through its association with Oct4 and ß-catenin and its promoter binding capability. These results establish that Bcl3 positively regulates pluripotency genes and thus shed light on the mechanism of Bcl3 as a downstream molecule of LIF/STAT3 signaling in pluripotency maintenance.

Injection of autologous bone marrow cells in hyaluronan hydrogel improves cardiac performance after infarction in pigs.

Intramyocardial injection of bone marrow mononuclear cells (MNCs) with hyaluronan (HA) hydrogel is beneficial to the ischemic heart in a rat model of myocardial infarction (MI). However, the therapeutic efficacy and safety must be addressed in large animals before moving onto a clinical trial. Therefore, the effect of combined treatment on MI was investigated in pigs. Coronary artery ligation was performed in minipigs to induce MI followed by an intramyocardial injection of normal saline (n = 7), HA (n = 7), normal saline with 1 × 10(8) freshly isolated MNCs (n = 8), or HA with 1 × 10(8) MNCs (HA-MNC; n = 7), with a sham-operated group serving as a control (n = 7). The response of each experimental group was estimated by echocardiography, ventricular catheterization, and histological analysis. Although injection of HA or MNCs slightly elevated left ventricular ejection fraction, the combined HA-MNC injection showed a significant increase in left ventricular ejection fraction, contractility, infarct size, and neovascularization. Importantly, injection of MNCs with HA also promoted MNC retention and MNC differentiation into vascular lineage cells in pigs. Therefore, this study not only provides evidence but also raises the possibility of using a combined HA-MNC injection as a promising therapy for heart repair.

Clearance kinetics of biomaterials affects stem cell retention and therapeutic efficacy.

The use of biomaterial carriers to improve the therapeutic efficacy of stem cells is known to augment cell delivery, retention, and viability. However, the way that carrier clearance kinetics boosts stem cell delivery and impacts stem cell function remains poorly characterized. In this study, we designed a platform to simultaneously quantify carrier clearance and stem cell retention to evaluate the impact of carrier clearance kinetics on stem cell retention. Additionally, a murine model of hindlimb ischemia was employed to investigate the effects of various cell retention profiles on mitigating peripheral arterial disease. To image the in vivo behaviors of material and cells, we used biotinylated hyaluronan with fluorescently labeled streptavidin and Discosoma sp. Red (Ds-Red)-expressing human mesenchymal stem cells. We found that the retention of transplanted stem cells was closely related to the remaining biomaterial. Furthermore, therapeutic effectiveness was also affected by stem cell retention. These results demonstrate that low-molecular-weight hyaluronan had a slow clearance and high cell retention profile, improving the therapeutic efficacy of human stem cells.

Evidence from a genetic fate-mapping study that stem cells refresh adult mammalian cardiomyocytes after injury.

An emerging concept is that the mammalian myocardium has the potential to regenerate, but that regeneration might be too inefficient to repair the extensive myocardial injury that is typical of human disease. However, the degree to which stem cells or precursor cells contribute to the renewal of adult mammalian cardiomyocytes remains controversial. Here we report evidence that stem cells or precursor cells contribute to the replacement of adult mammalian cardiomyocytes after injury but do not contribute significantly to cardiomyocyte renewal during normal aging. We generated double-transgenic mice to track the fate of adult cardiomyocytes in a 'pulse-chase' fashion: after a 4-OH-tamoxifen pulse, green fluorescent protein (GFP) expression was induced only in cardiomyocytes, with 82.7% of cardiomyocytes expressing GFP. During normal aging up to one year, the percentage of GFP+ cardiomyocytes remained unchanged, indicating that stem or precursor cells did not refresh uninjured cardiomyocytes at a significant rate during this period of time. By contrast, after myocardial infarction or pressure overload, the percentage of GFP+ cardiomyocytes decreased from 82.8% in heart tissue from sham-treated mice to 67.5% in areas bordering a myocardial infarction, 76.6% in areas away from a myocardial infarction, and 75.7% in hearts subjected to pressure overload, indicating that stem cells or precursor cells had refreshed the cardiomyocytes.

Hyaluronan enhances bone marrow cell therapy for myocardial repair after infarction.

Hyaluronan (HA) has been shown to play an important role during early heart development and promote angiogenesis under various physiological and pathological conditions. In recent years, stem cell therapy, which may reduce cardiomyocyte apoptosis, increase neovascularization, and prevent cardiac fibrosis, has emerged as a promising approach to treat myocardial infarction (MI). However, effective delivery of stem cells for cardiac therapy remains a major challenge. In this study, we tested whether transplanting a combination of HA and allogeneic bone marrow mononuclear cells (MNCs) promotes cell therapy efficacy and thus improves cardiac performance after MI in rats. We showed that HA provided a favorable microenvironment for cell adhesion, proliferation, and vascular differentiation in MNC culture. Following MI in rats, compared with the injection of HA alone or MNC alone, injection of both HA and MNCs significantly reduced inflammatory cell infiltration, cardiomyocyte apoptosis, and infarct size and also improved cell retention, angiogenesis, and arteriogenesis, and thus the overall cardiac performance. Ultimately, HA/MNC treatment improved vasculature engraftment of transplanted cells in the infarcted region. Together, our results indicate that combining the biocompatible material HA with bone marrow stem cells exerts a therapeutic effect on heart repair and may further provide potential treatment for ischemic diseases.

Human iPSC-derived Committed Cardiac Progenitors Generate Cardiac Tissue Grafts in a Swine Ischemic Cardiomyopathy Model without Triggering Ventricular Arrhythmias.

BACKGROUND: The adult human heart following a large myocardial infarction is unable to regenerate heart muscle and instead forms scar with the risk of progressive heart failure. Large animal studies have shown that intramyocardial injection of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) following a myocardial infarction result in cell grafts but also ventricular arrhythmias. We hypothesized that intramyocardial injection of committed cardiac progenitor cells (CCPs) derived from iPSCs, combined with cardiac fibroblast-derived extracellular matrix (cECM) to enhance cell retention will: i) form cardiomyocyte containing functional grafts, ii) be free of ventricular arrhythmias and iii) restore left ventricular contractility in a post-myocardial infarction (MI) cardiomyopathy swine model. METHODS: hiPSCs were differentiated using bioreactors and small molecules to produce a population of committed cardiac progenitor cells (CCPs). MI was created using a coronary artery balloon occlusion and reperfusion model in Yucatan mini pigs. Four weeks later, epicardial needle injections of CCPs+cECM were performed in a small initial feasibility cohort, and then transendocardial injections (TEI) of CCPs+cECM, CCPs alone, cECM alone or vehicle control into the peri-infarct region in a larger randomized cohort. A 4-drug immunosuppression regimen was administered to prevent rejection of human CCPs. Arrhythmias were evaluated using implanted event recorders. Magnetic resonance imaging (MRI) and invasive pressure volume assessment were used to evaluate left ventricular anatomic and functional performance, including viability. Detailed histology was performed on the heart to detect human grafts. RESULTS: A scalable biomanufacturing protocol was developed generating CCPs which can efficiently differentiate to cardiomyocytes or endothelial cells in vitro. Intramyocardial delivery of CCPs to post-MI porcine hearts resulted in engraftment and differentiation of CCPs to form ventricular cardiomyocyte rich grafts. There was no significant difference in cardiac MRI-based measured cardiac volumes or function between control, CCP and CCP+cECM groups; however, dobutamine stimulated functional reserve was improved in CCP and CCP+cECM groups. TEI delivery of CCPs with or without cECM did not result in tumors or trigger ventricular arrhythmias. CONCLUSIONS: CCPs are a promising cell source for post-MI heart repair using clinically relevant TEI with a low risk of engraftment ventricular arrhythmias.

Gut butyrate-producers confer post-infarction cardiac protection.

The gut microbiome and its metabolites are increasingly implicated in several cardiovascular diseases, but their role in human myocardial infarction (MI) injury responses have yet to be established. To address this, we examined stool samples from 77 ST-elevation MI (STEMI) patients using 16 S V3-V4 next-generation sequencing, metagenomics and machine learning. Our analysis identified an enriched population of butyrate-producing bacteria. These findings were then validated using a controlled ischemia/reperfusion model using eight nonhuman primates. To elucidate mechanisms, we inoculated gnotobiotic mice with these bacteria and found that they can produce beta-hydroxybutyrate, supporting cardiac function post-MI. This was further confirmed using HMGCS2-deficient mice which lack endogenous ketogenesis and have poor outcomes after MI. Inoculation increased plasma ketone levels and provided significant improvements in cardiac function post-MI. Together, this demonstrates a previously unknown role of gut butyrate-producers in the post-MI response.

Opportunities and Challenges of Human IPSC Technology in Kidney Disease Research.

Human induced pluripotent stem cells (iPSCs), since their discovery in 2007, open a broad array of opportunities for research and potential therapeutic uses. The substantial progress in iPSC reprogramming, maintenance, differentiation, and characterization technologies since then has supported their applications from disease modeling and preclinical experimental platforms to the initiation of cell therapies. In this review, we started with a background introduction about stem cells and the discovery of iPSCs, examined the developing technologies in reprogramming and characterization, and provided the updated list of stem cell biobanks. We highlighted several important iPSC-based research including that on autosomal dominant kidney disease and SARS-CoV-2 kidney involvement and discussed challenges and future perspectives.

Utility of iPSC-Derived Cells for Disease Modeling, Drug Development, and Cell Therapy.

The advent of induced pluripotent stem cells (iPSCs) has advanced our understanding of the molecular mechanisms of human disease, drug discovery, and regenerative medicine. As such, the use of iPSCs in drug development and validation has shown a sharp increase in the past 15 years. Furthermore, many labs have been successful in reproducing many disease phenotypes, often difficult or impossible to capture, in commonly used cell lines or animal models. However, there still remain limitations such as the variability between iPSC lines as well as their maturity. Here, we aim to discuss the strategies in generating iPSC-derived cardiomyocytes and neurons for use in disease modeling, drug development and their use in cell therapy.

PEGylation of Phosphatidylglycerol/Docosahexaenoic Acid Hexosomes with d-α-Tocopheryl Succinate Poly(ethylene glycol)2000 Induces Morphological Transformation into Vesicles with Prolonged Circulation Times.

Considering the broad therapeutic potential of omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA), here we study the effect of PEGylation of DHA-incorporated hexosomes on their physicochemical characteristics and biodistribution following intravenous injection into mice. Hexosomes were formed from phosphatidylglycerol and DHA with a weight ratio of 3:2. PEGylation was achieved through the incorporation of either d-α-tocopheryl succinate poly(ethylene glycol)2000 (TPGS-mPEG2000) or 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy-poly(ethylene glycol)2000 (DSPE-mPEG2000) at a concentration of 1.5 wt %. Nanoparticle tracking analysis, synchrotron small-angle scattering, and cryo-transmission electron microscopy were employed to characterize the nanodispersions. The results show that PEGylated lipids induce a structural transition from an inverse hexagonal (H2) phase inside the nanoparticles (hexosomes) to a lamellar (Lα) phase (vesicles). We also followed the effect of mouse plasma on the nanodispersion size distribution, number, and morphology because changes brought by plasma constituents could regulate the in vivo performance of intravenously injected nanodispersions. For comparative biodistribution studies, fluorescently labeled nanodispersions of equivalent quantum yields were injected intravenously into healthy mice. TPGS-mPEG2000-induced vesicles were most effective in avoiding hepatosplenic clearance at early time points. In an orthotopic xenograft murine model of glioblastoma, TPGS-mPEG2000-induced vesicles also showed improved localization to the brain compared with native hexosomes. We discuss these observations and their implications for the future design of injectable lyotropic nonlamellar liquid crystalline drug delivery nanosystems for therapeutic interventions of brain and liver diseases.

The gut microbiota regulates acute foreign body reaction and tissue repair after biomaterial implantation.

We hypothesized that the host microbiome may influence foreign body responses following biomaterial implantation. To test this, we implanted a variety of clinically relevant biomaterials into germ-free or antibiotic-treated mice. Surprisingly, these mice displayed less fibrous tissue deposition, reduced host cell recruitment to the implant site, and differential expression of angiogenic and inflammatory markers. These observations were reversed upon fecal microbiome reconstitution, confirming a causal role of the host microbiome. In a clinically relevant disease model, microbiome-depleted mice cleared hyaluronic acid and bone marrow mononuclear cells from ischemic hind limb tissues more slowly, resulting in an improved therapeutic response. Findings were confirmed in pigs which showed reduced fibrotic responses to a variety of implanted materials. Lastly, we profiled changes in the host microbiome following material implantation, implicating several key bacteria phyla.