Project description:Limb regeneration, while observed lifelong in salamanders, is restricted to pre-metamorphic stages in Xenopus laevis frogs. After amputation, post-metamorphic frogs form a blastema that grows only an unsegmented cartilage rod. Whether this loss is due to systemic factors such as the immune system or due to an intrinsic incapability of cells to form competent stem cells has been unclear. Here, we use genetic fate mapping to establish that, as in axolotl, connective tissue (CT) cells form the post-metamorphic frog blastema. Using heterochronic transplantation into the limb bud and single-cell transcriptomic profiling, we show that axolotl CT cells fully dedifferentiate and integrate to form lineages including cartilage in the developing limb. In contrast, frog blastema CT cells do not fully re-express the limb bud progenitor program, even when transplanted into the limb bud. Correspondingly, transplanted cells contribute to extraskeletal CT but not to developing cartilage. Further, using single-cell RNA-seq analysis we find that the embryonic and the adult frog cartilage differentiation programs are molecularly distinct. This work defines intrinsic restrictions in CT dedifferentiation as a limitation in adult regeneration.
Project description:Mammalian tissues have a limited regenerative capacity. Previous studies showed that dedifferentiation contributes to tissue regeneration in non-mammalian vertebrate species such as zebrafish and newt. However, dedifferentiation is rarely observed in mammalian tissues even in the neonatal stage and therefore artificial induction of dedifferentiation might enhance regeneration in mammalian tissues. Here we demonstrate that short-term expression of Yamanaka 4 factors (4F) induces dedifferentiation and proliferation in the liver by using lineage-traceable, hepatocyte-specific 4F inducible mouse model. Global transcriptome analysis shows that 4F expression transiently reduces the expression of hepatic-lineage markers and induces the expression of a large set of proliferative markers and epigenetic modifiers along with global epigenetic changes as assessed by DNA-accessibility analysis. More importantly, lineage-tracing experiments showed that 4F-expressing hepatocytes acquire liver stem/progenitor cell markers, suggesting that 4F induces partial reprogramming. Moreover, 4F enhances MyoD-mediated transdifferentiation in the liver, suggesting that 4F endows hepatocytes with plasticity. Lastly, 4F expression attenuated liver injury associated with more proliferative capacity and better survival rate, indicating that 4F enhances liver regeneration. Taken together, these results demonstrate that liver-specific 4F expression induces dedifferentiation and promotes liver regeneration.
Project description:The liverM-bM-^@M-^Ys remarkable capacity to regenerate allows it to carry out vital life-supporting functions despite unrelenting pathogen and toxin-induced injury. Unchecked, this capability also leads to cirrhosis, a burgeoning global disease burden. Existing animal models only partially recapitulate human liver regeneration, which hitherto has not been systematically studied. We investigated human liver regeneration in a unique model of liver transplantation. Here we show coordinated changes in expression of microRNA (miRNA) during regeneration that drive proliferation, innate immunity and angiogenesis. Failed regeneration is associated with distinct miRNAs enforcing cell cycle inhibition and DNA methylation. The miRNA expression associated with successful or failed regeneration when recapitulated in vitro, triggered expression of cardinal regeneration-linked genes promoting cell cycle entry or inhibition, respectively. Furthermore, inhibition of three miRNAs whose downregulation is associated with successful regeneration, induced proliferation in vitro. Our data indicate that human liver regeneration is orchestrated by distinct miRNAs determining cell cycle fate. Their manipulation may obviate the need for transplantation by enforcing successful regeneration in the liver and other solid organs. We compared a group of seven patients with successful regeneration (RG) after auxiliary liver transplant (ALT) to four patients who also had ALT but failed to regenerate (NRG). Regeneration was quantified by volume expansion using radiographic imaging; functional recovery was assessed using nuclear isotope scanning and hepatocellular regeneration using histology. Based on histological assessment, three time points were selected for both groups (RG and NRG). Biopsies were taken at the time of transplant and at different intervals post-transplant. Since sample acquisition was driven by clinical necessity, widely discrepant time intervals existed between T=1, T=2 and T=3 for the patients. RNA was extracted from archived histology samples of the RG and NRG, and miRNA expression was analysed using the Affymetrix GeneChip miRNA 1.0 assays. This submission does not include NRG samples taken at time point 3.
Project description:The liver’s remarkable capacity to regenerate allows it to carry out vital life-supporting functions despite unrelenting pathogen and toxin-induced injury. Unchecked, this capability also leads to cirrhosis, a burgeoning global disease burden. Existing animal models only partially recapitulate human liver regeneration, which hitherto has not been systematically studied. We investigated human liver regeneration in a unique model of liver transplantation. Here we show coordinated changes in expression of microRNA (miRNA) during regeneration that drive proliferation, innate immunity and angiogenesis. Failed regeneration is associated with distinct miRNAs enforcing cell cycle inhibition and DNA methylation. The miRNA expression associated with successful or failed regeneration when recapitulated in vitro, triggered expression of cardinal regeneration-linked genes promoting cell cycle entry or inhibition, respectively. Furthermore, inhibition of three miRNAs whose downregulation is associated with successful regeneration, induced proliferation in vitro. Our data indicate that human liver regeneration is orchestrated by distinct miRNAs determining cell cycle fate. Their manipulation may obviate the need for transplantation by enforcing successful regeneration in the liver and other solid organs.
Project description:Defining conserved molecular pathways in animal models of successful cardiac regeneration could yield insight into why adult mammals have inadequate cardiac regeneration after injury. Here we describe a cross-species transcriptomic screen to identify evolutionarily conserved pathways in the early events of cardiac regeneration in three species that can regenerate myocardium after a major injury. In this study, we performed RNA-seq on regenerating hearts from three model organisms - axolotl, zebrafish and mouse. Apical resection was performed to amputate ~10 - 20% of the left ventricle in all three model organisms. Following resection, hearts were harvested at 12, 24 and 48 hours post-resection and subjected to RNA-seq. RNA-seq on sham controls (no ventricular amputation) was used as interanal control. This approach revealed upregulation of inflammatory genes in all three organisms during regeneration. Furthermore, upregulation of Complement 5a receptor1 (C5aR1) expression in the regenerating hearts of zebrafish, axolotls and mice was observed.
Project description:Mammalian skin wounds heal by forming fibrotic scars. We report that reindeer antler velvet exhibits regenerative wound healing, whereas identical injury to back skin forms scar. This regenerative capacity was retained following ectopic transplantation of velvet to scar-forming sites. Single-cell mRNA/ATAC-Sequencing revealed that while uninjured velvet fibroblasts resembled human fetal fibroblasts, back skin fibroblasts were enriched in pro-inflammatory features resembling adult human fibroblasts. Injury elicited site-specific immune polarization; back skin fibroblasts amplified the immune response, whereas velvet fibroblasts adopted an immunosuppressive state leading to restrained myeloid maturation and hastened immune resolution ultimately enabling myofibroblast reversion to a regeneration-competent state. Finally, regeneration was blunted following application of back skin associated immunostimulatory signals or inhibition of pro-regenerative factors secreted exclusive to velvet fibroblasts. This study highlights a unique model to interrogate mechanisms underlying divergent healing outcomes and nominates both decoupling of stromal-immune crosstalk and reinforcement of pro-regenerative fibroblast programs to mitigate scar.
Project description:Rationale: In virtually all models of heart failure, prognosis is determined by right ventricular (RV) function; thus, understanding the cellular mechanisms contributing to RV dysfunction is critical. Whole organ remodeling is associated with cell-specific changes, including cardiomyocyte dedifferentiation and activation of cardiac fibroblasts (Cfib) which in turn is linked to disorganization of cytoskeletal proteins and loss of sarcomeric structures. However, how these cellular changes contribute to RV function remains unknown. We’ve previously shown significant organ-level RV dysfunction in a large animal model of pulmonary hypertension (PH) which was not mirrored by reduced function of isolated cardiomyocytes. We hypothesized that factors produced by the endogenous Cfib contribute to global RV dysfunction by generating a heterogeneous cellular environment populated by dedifferentiated cells. Objective: To determine the effect of Cfib conditioned media (CM) from the PH calf (PH-CM) on adult rat ventricular myocytes (ARVM) in culture. Methods and Results: Brief exposure (<2 days) to PH-CM results in rapid, marked dedifferentiation of ARVM to a neonatal-like phenotype exhibiting spontaneous contractile behavior. Dedifferentiated cells maintain viability for over 30 days with continued expression of cardiomyocyte proteins including TnI and α-actinin yet exhibit myofibroblast characteristics including expression of α-smooth muscle actin. Using a bioinformatics approach to identify factor(s) that contribute to dedifferentiation, we found activation of the PH Cfib results in a unique transcriptome correlating with factors both in the secretome and with activated pathways in the dedifferentiated myocyte. Further, we identified upregulation of periostin in the Cfib and CM, and demonstrate that periostin is sufficient to drive cardiomyocyte dedifferentiation. Conclusions: These data suggest that paracrine factor(s) released by Cfib from the PH calf signal a phenotypic transformation in a population of cardiomyocytes that likely contributes to RV dysfunction. Therapies targeting this process, such as inhibition of periostin, have the potential to prevent RV dysfunction.