In response to injury, a variety of different cells are recruited to sites of injury to facilitate healing. Recent studies have examined the importance of the heterogeneity of tissue resident fibroblasts and mechanical signalling pathways in healing and fibrosis. However, tissue repair and the inflammatory response also involves blood cells that are recruited from the circulation. Here we identify mechanoresponsive myeloid subpopulations present in scar and unwounded skin. We then modulate these subpopulations by manipulating mechanical strain in vivo and in vitro and find that specifically targeting myeloid mechanical signalling is sufficient to reduce the pro-fibrotic myeloid subpopulations and restore the native, anti-inflammatory subpopulations. In addition, myeloid-specific mechanotransduction ablation also downregulates downstream pro-fibrotic fibroblast transcriptional profiles, reducing scar formation. As inflammatory cells circulate and home to injury sites during the initial healing phases in all organs, focusing on mechanoresponsive myeloid subpopulations may generate additional directions for systemic immunomodulatory therapies to target fibrosis and other diseases across other internal organ systems. Myeloid-specific mechanotransduction ablation downregulates pro-fibrotic fibroblast transcriptional profiles to reduce scar formation in human cells

Background. Combined heart liver transplant (CHLT) continues to gain attention as a surgical treatment for patients with end-stage heart and liver disease but remains rare. We present our institutional longitudinal experience with up to 14 y of follow-up, focused on long-term outcomes in CHLT recipients. Methods. We conducted a single-institutional, retrospective review from January 1, 2010, to December 31, 2023, including 7 patients ages 7–17 y who underwent CHLT. Results. Most patients were surgically palliated via Fontan procedure pretransplant (n = 6), and all had evidence of advanced fibrosis or cirrhosis before transplant. The 30-d mortality was 14.3% (n = 1, multiorgan failure). During the follow-up period, 1 patient developed acute heart rejection which required treatment and 2 developed acute liver rejection. In all cases, rejection was successfully treated. Two patients developed acute heart rejection which did not require treatment (grade 1R). No patients developed chronic or refractory rejection. No patients developed allograft coronary artery vasculopathy. Conclusions. CHLT remains a rarely performed treatment for pediatric patients with end-stage heart and liver disease, but our long-term data suggest that this treatment strategy should be considered more frequently.

BACKGROUND:The SARS-CoV-2 pandemic and corresponding acute respiratory syndrome have affected all populations and led to millions of deaths worldwide. The pandemic disproportionately affected immunocompromised and immunosuppressed adult patients who had received solid organ transplants (SOTs). With the onset of the pandemic, transplant societies across the world recommended reducing SOT activities to avoid exposing immunosuppressed recipients. Due to the risk of COVID-19-related outcomes, SOT providers adapted the way they deliver care to their patients, leading to a reliance on telehealth. Telehealth has helped organ transplant programs continue treatment regimens while protecting patients and physicians from COVID-19 transmission. This review highlights the adverse effects of COVID-19 on transplant activities and summarizes the increased role of telehealth in the management of solid organ transplant recipients (SOTRs) in both pediatric and adult populations.METHODS:A comprehensive systematic review and meta-analysis were conducted to accentuate the outcomes of COVID-19 and analyze the efficacy of telehealth on transplant activities. This in-depth examination summarizes extensive data on the clinical detriments of COVID-19 in transplant recipients, advantages, disadvantages, patient/physician perspectives, and effectiveness in transplant treatment plans via telehealth.RESULTS:COVID-19 has caused an increase in mortality, morbidity, hospitalization, and ICU admission in SOTRs. Telehealth efficacy and benefits to both patients and physicians have increasingly been reported.CONCLUSIONS:Developing effective systems of telehealth delivery has become a top priority for healthcare providers during the COVID-19 pandemic. Further research is necessary to validate the effectiveness of telehealth in other settings.

Small animals do not replicate the severity of the human foreign-body response (FBR) to implants. Here we show that the FBR can be driven by forces generated at the implant surface that, owing to allometric scaling, increase exponentially with body size. We found that the human FBR is mediated by immune-cell-specific RAC2 mechanotransduction signalling, independently of the chemistry and mechanical properties of the implant, and that a pathological FBR that is human-like at the molecular, cellular and tissue levels can be induced in mice via the application of human-tissue-scale forces through a vibrating silicone implant. FBRs to such elevated extrinsic forces in the mice were also mediated by the activation of Rac2 signalling in a subpopulation of mechanoresponsive myeloid cells, which could be substantially reduced via the pharmacological or genetic inhibition of Rac2 . Our findings provide an explanation for the stark differences in FBRs observed in small animals and humans, and have implications for the design and safety of implantable devices.

Chronic wounds impose a significant healthcare burden to a broad patient population. Cell based therapies, while having shown benefits for the treatment of chronic wounds, have not achieved widespread adoption into clinical practice. Here, we developed a novel CRISPR/Cas9 approach to precisely edit dendritic cells (DCs) to enhance their therapeutic potential for healing chronic wounds. Using single-cell RNA sequencing (scRNA-seq) of tolerogenic DCs, we discover N-myc downregulated gene 2 (Ndrg2), which marks a specific population of DC progenitors, as a promising target for CRISPR knockout (KO). Ndrg2-KO alters the transcriptomic profile of DCs and preserves an immature cell state with a strong, pro-angiogenic and regenerative capacity. We then incorporated our CRISPR-based cell engineering within a hydrogel technology for in vivo cell delivery and developed a highly effective translational approach for DC based immunotherapy that accelerated healing of full-thickness wounds in both non-diabetic and diabetic mouse models. These findings could open the door to future clinical trials using safe gene editing in DCs for treating various types of chronic wounds.

BACKGROUND:Capsular fibrosis (CF) often occurs around biomedical devices following implantation causing pain, discomfort, and device failure. Breast implantation remains among the most common medical procedures worldwide. Revealing specific genes that drive fibrotic deposition will help us to garner a better understanding of the pathophysiology of this disease and develop different strategies to combat it. METHODS:The authors collected 631 capsules around breast implants and were able to connect clinical baseline characteristics with histopathologic findings. In addition, the authors were able to conduct the first large systematic analysis to identify differentially expressed genes in fibrotic human tissue samples, comparing the lowest form of fibrosis with the most aggravated one. RESULTS:The authors identified 2559 differentially expressed genes on which they performed a knowledge-based network generation and pathway association study to identify putative novel biomarkers for CF. The authors were able to show changes of cellular influx during progression of CF and distinguish several genes as potential clinical biomarkers and drug targets. Among these, matrix metalloproteinase-9 was one of the most up-regulated ( P = 0.006) and is attractive because of its wide detectability. CONCLUSIONS:Matrix metalloproteinase-9 seems to be a potential biomarker to detect capsular fibrosis. It is a measurable indicator that can easily be detected in blood, sputum, and urine. For the diagnosis of fibrosis, this biomarker might be exceedingly beneficial to developing novel screening methods and prophylaxes. CLINICAL RELEVANCE STATEMENT:Discovering biomarkers at the earliest and mildest stages for the diagnosis of fibrosis is clinically important. These results bring new hope for biomarker-based diagnosis for capsular fibrosis. CLINICAL QUESTION/LEVEL OF EVIDENCE:Diagnostic, V.

Mesenchymal stem cells are under investigation as a novel therapy to treat solid organ transplant rejection. However, significant hurdles have limited their use in humans. Mesenchymal stem cell-derived extracellular vesicles address many of these shortcomings but have not been investigated clinically. Here we report our experience treating 2 patients with graft rejection and inflammation following a bowel transplant using mesenchymal stem cell-derived extracellular vesicles.

The authors have no conflicts of interest to disclose. The data that support the findings of this study are available from the corresponding author upon reasonable request.

Cardiovascular disease is one of the leading causes of morbidity and mortality worldwide, with myocardial infarctions being amongst the deadliest manifestations. Reduced blood flow to the heart can result in the death of cardiac tissue, leaving affected patients susceptible to further complications and recurrent disease. Further, contemporary management typically involves a pharmacopeia to manage the metabolic conditions contributing to atherosclerotic and hypertensive heart disease, rather than regeneration of the damaged myocardium. With modern healthcare extending lifespan, a larger demographic will be at risk for heart disease, driving the need for novel therapeutics that surpass those currently available in efficacy. Transdifferentiation and cellular reprogramming have been looked to as potential methods for the treatment of diseases throughout the body. Specifically targeting the fibrotic cells in cardiac scar tissue as a source to be reprogrammed into induced cardiomyocytes remains an appealing option. This review aims to highlight the history of and advances in cardiac reprogramming and describe its translational potential as a treatment for cardiovascular disease.

Purpose: Repair after tissue injury involves a dynamic interplay among not just tissue resident cells (e.g., fibroblasts), but also cells recruited from the circulation. Myeloid cells, such as monocytes and macrophages, are derived from hematopoietic precursors and migrate to sites of injury where they play a role in modulating all stages of wound healing and scar formation. There is mounting evidence that mechanical stimuli are also able to modulate monocyte and macrophage response during tissue healing, but the exact mechanisms behind this “mechano-immunomodulation” remain incompletely understood. Methods: We attached a mechanical strain device to the mouse dorsum to initiate a uniform and consistent strain profile across an incisional wound to create hypertrophic scar (HTS) formation in mice. To investigate mechano-responsive immune cells, we performed parabiosis of wildtype (WT) and GFP+ mice, allowed the mice to develop a shared blood circulation, initiated HTS formation in the WT mouse, and analyzed the cells using single cell RNA sequencing (scRNA-seq), fluorescent-activated cell sorting (FACS), and immunofluorescent staining. Results: Mechanical modulation significantly upregulated the presence of inflammatory subtypes within the healing tissue, characterized by an increase in infiltrating GFP+ cells from 5.4% to 12.2%. In the GFP+ circulating cells, mechanical strain directly increased the proportion of fibrotic myeloid cells, primarily defined by the monocyte marker Ly6c2 as well as the TGFB responsive and macrophage activating gene Thbs1. Mechanical strain also increased the proportion of inflammatory myeloid cell populations, defined by Ccl and Il6 chemoattractants, and Cd74+ migratory myeloid cells. Utilizing both a pharmacological blocker of focal adhesion kinase (FAK) as well as a myeloid specific FAK knockout (KO), we demonstrated that modulating mechanical signaling abrogated those responses and instead promoted homeostatic myeloid transcriptional fates. Conclusion: Tissue injury activates a cascade of signaling pathways to recruit and orchestrate various cell types during healing. Our study indicates that modulating mechanical stress directly affects myeloid cell phenotypes and interactions with other cell types in the complicated, multicellular milieu of wound healing. This principle has been previously unexplored in the context of fibrosis and regeneration, with most previous studies focused on fibroblast heterogeneity and transcriptional profiles. To our knowledge, this is the first study to directly investigate the effects of modulating mechanotransduction on immune cell response at the single cell level utilizing parabiosis and wound healing. Collectively, we demonstrate that mechano-immunomodulation of the “early responders” of healing can trigger a cascade of downstream regenerative healing.

Burns and other traumatic injuries represent a substantial biomedical burden. The current standard of care for deep injuries is autologous split-thickness skin grafting (STSG), which frequently results in contractures, abnormal pigmentation, and loss of biomechanical function. Currently, there are no effective therapies that can prevent fibrosis and contracture after STSG. Here, we have developed a clinically relevant porcine model of STSG and comprehensively characterized porcine cell populations involved in healing with single-cell resolution. We identified an up-regulation of proinflammatory and mechanotransduction signaling pathways in standard STSGs. Blocking mechanotransduction with a small-molecule focal adhesion kinase (FAK) inhibitor promoted healing, reduced contracture, mitigated scar formation, restored collagen architecture, and ultimately improved graft biomechanical properties. Acute mechanotransduction blockade up-regulated myeloid CXCL10-mediated anti-inflammation with decreased CXCL14-mediated myeloid and fibroblast recruitment. At later time points, mechanical signaling shifted fibroblasts toward profibrotic differentiation fates, and disruption of mechanotransduction modulated mesenchymal fibroblast differentiation states to block those responses, instead driving fibroblasts toward proregenerative, adipogenic states similar to unwounded skin. We then confirmed these two diverging fibroblast transcriptional trajectories in human skin, human scar, and a three-dimensional organotypic model of human skin. Together, pharmacological blockade of mechanotransduction markedly improved large animal healing after STSG by promoting both early, anti-inflammatory and late, regenerative transcriptional programs, resulting in healed tissue similar to unwounded skin. FAK inhibition could therefore supplement the current standard of care for traumatic and burn injuries.

For decades, it has been assumed that the foreign body response (FBR) to biomedical implants is primarily a reaction to the chemical and mechanical properties of the implant. Here, we show for the first time that a third independent variable, allometric tissue-scale forces (which increase exponentially with body size), can drive the biology of FBR in humans. We first demonstrate that pathological FBR in humans is mediated by immune cell-specific Rac2 mechanotransduction signaling, independent of implant chemistry or mechanical properties. We then show that mice, which are typically poor models of human FBR, can be made to induce a strikingly human-like pathological FBR by altering these extrinsic tissue forces. Altering these extrinsic tissue forces alone activates Rac2 signaling in a unique subpopulation of immune cells and results in a human-like pathological FBR at the molecular, cellular, and local tissue levels. Finally, we demonstrate that blocking Rac2 signaling negates the effect of increased tissue forces, dramatically reducing FBR. These findings highlight a previously unsuspected mechanism for pathological FBR and may have profound implications for the design and safety of all implantable devices in humans. One-Sentence Summary Allometric tissue-scale forces at the implant-tissue interface drive pathological foreign body response.

Background During the donor hepatectomy time (dHT), defined as the time from the start of cold perfusion to the end of the hepatectomy, liver grafts have a suboptimal temperature. The aim of this study was to analyze the impact of prolonged dHT on outcomes in donation after circulatory death (DCD) liver transplantation (LT). Methods Using the US national registry data between 2012 and 2020, DCD LT patients were separated into two groups based on their dHT: standard dHT (< 42 min) and prolonged dHT (>= 42 min). Results There were 3810 DCD LTs during the study period. Median dHT was 32 min (interquartile range 25-41 min). Kaplan-Meier graft survival curves demonstrated inferior outcomes in the prolonged dHT group at 1-year after DCD LT compared to those in the standard dHT group (85.3% vs 89.9%; P < .01). Multivariate Cox proportional hazards models for 1-year graft survival identified that prolonged dHT [hazard ratio (HR) 1.46, 95% confidence interval (CI) 1.19 - 1.79], recipient age >= 64 years (HR 1.40, 95% CI 1.14 - 1.72), and MELD score >= 24 (HR 1.43, 95% CI 1.16 - 1.76) were significant predictors of 1-year graft loss. Spline analysis shows that the dHT effects on the risk for 1-year graft loss with an increase in the slope after median dHT of 32 min. Conclusion Prolonged dHTs significantly reduced graft and patient survival after DCD LT. Because dHT is a modifiable factor, donor surgeons should take on cases with caution by setting the dHT target of < 32 min.

Regeneration is the holy grail of tissue repair, but skin injury typically yields fibrotic, non-functional scars. Developing pro-regenerative therapies requires rigorous understanding of the molecular progression from injury to fibrosis or regeneration. Here, we report the divergent molecular events driving skin wound cells toward scarring or regenerative fates. We profile scarring versus YAP-inhibition-induced wound regeneration at the transcriptional (single-cell RNA sequencing), protein (timsTOF proteomics), and tissue (extracellular matrix ultrastructural analysis) levels. Using cell-surface barcoding, we integrate these data to reveal fibrotic and regenerative "molecular trajectories"of healing. We show that disrupting YAP mechanotransduction yields regenerative repair by fibroblasts with activated Trps1 and Wnt signaling. Finally, via in vivo gene knockdown and overexpression in wounds, we identify Trps1 as a key regulatory gene that is necessary and partially sufficient for wound regeneration. Our findings serve as a multi-omic map of wound regeneration and could have therapeutic implications for pathologic fibroses.