Aspartate signalling drives lung metastasis via alternative translation

Lung metastases occur in up to 54% of patients with metastatic tumours1,2. Contributing factors to this high frequency include the physical properties of the pulmonary system and a less oxidative environment that may favour the survival of cancer cells3. Moreover, secreted factors from primary tumours alter immune cells and the extracellular matrix of the lung, creating a permissive pre-metastatic environment primed for the arriving cancer cells4,5. Nutrients are also primed during pre-metastatic niche formation6. Yet, whether and how nutrients available in organs in which tumours metastasize confer cancer cells with aggressive traits is mostly undefined. Here we found that pulmonary aspartate triggers a cellular signalling cascade in disseminated cancer cells, resulting in a translational programme that boosts aggressiveness of lung metastases. Specifically, we observe that patients and mice with breast cancer have high concentrations of aspartate in their lung interstitial fluid. This extracellular aspartate activates the ionotropic N-methyl-D-aspartate receptor in cancer cells, which promotes CREB-dependent expression of deoxyhypusine hydroxylase (DOHH). DOHH is essential for hypusination, a post-translational modification that is required for the activity of the non-classical translation initiation factor eIF5A. In turn, a translational programme with TGFβ signalling as a central hub promotes collagen synthesis in lung-disseminated breast cancer cells. We detected key proteins of this mechanism in lung metastases from patients with breast cancer. In summary, we found that aspartate, a classical biosynthesis metabolite, functions in the lung environment as an extracellular signalling molecule to promote aggressiveness of metastases.

Transforming growth factor-β signalling pathway in tendon healing

Transforming growth factor-β(TGF-β) plays an important but diverse role in tendon injuries, such as collagen synthesis, cell proliferation, cell differentiation, and cell adhesion, leading to tendon healing and tendon fibrosis. In the well-known canonical TGF-β signalling pathway, TGF-β activates Smad signalling through its two cell surface receptors, which leads to Smad-mediated transcriptional regulation and is also regulated by inhibitory Smads, forming a negative feedback regulatory pathway. In the context of the canonical TGF-β signalling mechanism mediated by Smad, the activated receptors also send signals through other signal transducers, which in the backdrop of TGF-β signaling are collectively known as non-Smad signalling pathways. Activated TGF-β binds to the receptor and acts through these signalling pathways. Understanding the mechanism of the TGF-β signalling pathway and its role in tendon repair is of great significance for targeting the TGF-β signalling pathway to accelerate tendon healing and reduce tendon fibrosis.

Prediction of CIAPIN1 (Cytokine-Induced Apoptosis Inhibitor 1) Signaling Pathway and Its Role in Cholangiocarcinoma Metastasis

Cholangiocarcinoma (CCA), a malignancy of the biliary epithelium, can arise at any point in the biliary system. We previously reported that CIAPIN1 is detectable in the sera and that its overexpression was associated with poor prognosis and metastasis of CCA patients. In this study, we investigated further its expression in CCA tissues, biological functions, and related signaling pathways in CCA cells. First, we examined CIAPIN1 expression in CCA tissues of 39 CCA patients using immunohistochemistry (IHC). Then, CIAPIN1-related proteins expressed in CCA cells were identified using RNA interference (siRNA) and liquid chromatography–mass spectrometry (LC–MS/MS). To predict the functions and signaling pathways of CIAPIN1 in CCA cells, the identified proteins were analyzed using bioinformatics tools. Then, to validate the biological functions of CIAPIN1 in the CCA cell line, transwell migration/invasion assays were used. CIAPIN1 was overexpressed in CCA tissues compared with adjacent noncancerous tissues. Its overexpression was correlated with lymph node metastasis. Bioinformatic analyses predicted that CIAPIN1 is connected to the TGF-β/SMADs signaling pathway via nitric oxide synthase 1 (NOS1) and is involved in the metastasis of CCA cells. In fact, cell migration and invasion activities of the KKU-100 CCA cell line were significantly suppressed by CIAPIN1 gene silencing. Our results unravel its novel function and potential signaling pathway in metastasis of CCA cells. CIAPIN1 can be a poor prognostic factor and can be a promising target molecule for CCA chemotherapy.

Functional Genomic Screening During Somatic Cell Reprogramming Identifies DKK3 as a Roadblock of Organ Regeneration

Somatic cell reprogramming and tissue repair share relevant factors and molecular programs. Here, Dickkopf-3 (DKK3) is identified as novel factor for organ regeneration using combined transcription-factor-induced reprogramming and RNA-interference techniques. Loss of Dkk3 enhances the generation of induced pluripotent stem cells but does not affect de novo derivation of embryonic stem cells, three-germ-layer differentiation or colony formation capacity of liver and pancreatic organoids. However, DKK3 expression levels in wildtype animals and serum levels in human patients are elevated upon injury. Accordingly, Dkk3-null mice display less liver damage upon acute and chronic failure mediated by increased proliferation in hepatocytes and LGR5+ liver progenitor cell population, respectively. Similarly, recovery from experimental pancreatitis is accelerated. Regeneration onset occurs in the acinar compartment accompanied by virtually abolished canonical-Wnt-signaling in Dkk3-null animals. This results in reduced expression of the Hedgehog repressor Gli3 and increased Hedgehog-signaling activity upon Dkk3 loss. Collectively, these data reveal Dkk3 as a key regulator of organ regeneration via a direct, previously unacknowledged link between DKK3, canonical-Wnt-, and Hedgehog-signaling.

Tgf-β superfamily and limb regeneration: Tgf-β to start and Bmp to end

Axolotls represent a popular model to study how nature solved the problem of regenerating lost appendages in tetrapods. Our work over many years focused on trying to understand how these animals can achieve such a feat and not end up with a scarred up stump. The Tgf-β superfamily represents an interesting family to target since they are involved in wound healing in adults and pattern formation during development. This family is large and comprises Tgf-β, Bmps, activins and GDFs. In this review, we present work from us and others on Tgf-β & Bmps and highlight interesting observations between these two sub-families. Tgf-β is important for the preparation phase of regeneration and Bmps for the redevelopment phase and they do not overlap with one another. We present novel data showing that the Tgf-β non-canonical pathway is also not active during redevelopment. Finally, we propose a molecular model to explain how Tgf-β and Bmps maintain distinct windows of expression during regeneration in axolotls.

Inhibition of TGF-β/Smad3 Signaling Disrupts Cardiomyocyte Cell Cycle Progression and Epithelial-Mesenchymal Transition-Like Response During Ventricle Regeneration

Unlike mammals, zebrafish can regenerate injured hearts even in the adult stage. Cardiac regeneration requires the coordination of cardiomyocyte (CM) proliferation and migration. The TGF-β/Smad3 signaling pathway has been implicated in cardiac regeneration, but the molecular mechanisms by which this pathway regulates CM proliferation and migration have not been fully illustrated. Here, we investigated the function of TGF-β/Smad3 signaling in a zebrafish model of ventricular ablation. Multiple components of this pathway were upregulated/activated after injury. Utilizing a specific inhibitor of Smad3, we detected an increased ratio of unrecovered hearts. Transcriptomic analysis suggested that the TGF-β/Smad3 signaling pathway could affect CM proliferation and migration. Further analysis demonstrated that the CM cell cycle was disrupted and the epithelial–mesenchymal transition (EMT)-like response was impaired, which limited cardiac regeneration. Altogether, our study reveals an important function of TGF-β/Smad3 signaling in CM cell cycle progression and EMT process during zebrafish ventricle regeneration.

Towards comparative analyses of salamander limb regeneration

Among tetrapods, only salamanders can regenerate their limbs and tails throughout life. This amazing regenerative ability has attracted the attention of scientists for hundreds of years. Now that large, salamander genomes are beginning to be sequenced for the first time, omics tools and approaches can be used to integrate new perspectives into the study of tissue regeneration. Here we argue the need to move beyond the primary salamander models to investigate regeneration in other species. Salamanders at first glance come across as a phylogenetically conservative group that has not diverged greatly from their ancestors. While salamanders do present ancestral characteristics of basal tetrapods, including the ability to regenerate limbs, data from fossils and data from studies that have tested for species differences suggest there may be considerable variation in how salamanders develop and regenerate their limbs. We review the case for expanded studies of salamander tissue regeneration and identify questions and approaches that are most likely to reveal commonalities and differences in regeneration among species. We also address challenges that confront such an initiative, some of which are regulatory and not scientific. The time is right to gain evolutionary perspective about mechanisms of tissue regeneration from comparative studies of salamander species.

The complexity of TGFβ/activin signaling in regeneration

The role of transforming growth factor β TGFβ/activin signaling in wound repair and regeneration is highly conserved in the animal kingdom. Various studies have shown that TGF-β/activin signaling can either promote or inhibit different aspects of the regeneration process (i.e., proliferation, differentiation, and re-epithelialization). It has been demonstrated in several biological systems that some of the different cellular responses promoted by TGFβ/activin signaling depend on the activation of Smad-dependent or Smad-independent signal transduction pathways. In the context of regeneration and wound healing, it has been shown that the type of R-Smad stimulated determines the different effects that can be obtained. However, neither the possible roles of Smad-independent pathways nor the interaction of the TGFβ/activin pathway with other complex signaling networks involved in the regenerative process has been studied extensively. Here, we review the important aspects concerning the TGFβ/activin signaling pathway in the regeneration process. We discuss data regarding the role of TGF-β/activin in the most common animal regenerative models to demonstrate how this signaling promotes or inhibits regeneration, depending on the cellular context.

Exosomes derived from tendon stem cells promote cell proliferation and migration through the TGF β signal pathway

Tendon stem cells (TSCs) are a kind of progenitor cells found in tendon niches, which play a key role in the repair of tendon injuries. Exosomes that mediate cell communication are involved in physiological processes and various diseases, while the effect of exosomes derived from TSCs (TSC-exo) on TSCs is still unclear. The purpose of this study is to explore the effect of TSC-exo on TSCs. Analyzing the characteristics of TSC-exo, we found that the TSC-exo were enriched in a large amount of transforming growth factor β (TGF β) by western blotting. We also found that the TGF β carried by TSC-exo can effectively accelerate the proliferation and migration of TSCs. We further found that TGF β carried by TSC-exo can activate the TGF β-Smad2/3 and the ERK1/2 signaling pathway in TSCs. Furthermore, matrix metalloenzyme 2 (MMP2), a downstream molecule of Smad2, is regulated by TGF β carried by TSC-exo. Collectively, our findings provide molecular insights into TSC-exo and indicate that TSC-exo are a potential strategy for treating tendon injuries.

The Epithelial-to-Mesenchymal Transition as a Possible Therapeutic Target in Fibrotic Disorders

Fibrosis is a chronic and progressive disorder characterized by excessive deposition of extracellular matrix, which leads to scarring and loss of function of the affected organ or tissue. Indeed, the fibrotic process affects a variety of organs and tissues, with specific molecular background. However, two common hallmarks are shared: the crucial role of the transforming growth factor-beta (TGF-β) and the involvement of the inflammation process, that is essential for initiating the fibrotic degeneration. TGF-β in particular but also other cytokines regulate the most common molecular mechanism at the basis of fibrosis, the Epithelial-to-Mesenchymal Transition (EMT). EMT has been extensively studied, but not yet fully explored as a possible therapeutic target for fibrosis. A deeper understanding of the crosstalk between fibrosis and EMT may represent an opportunity for the development of a broadly effective anti-fibrotic therapy. Here we report the evidences of the relationship between EMT and multi-organ fibrosis, and the possible therapeutic approaches that may be developed by exploiting this relationship.

BMP signaling is essential for sustaining proximo-distal progression in regenerating axolotl limbs

Amputation of a salamander limb triggers a regeneration process that is perfect. A limited number of genes have been studied in this context and even fewer have been analyzed functionally. In this work, we use the BMP signaling inhibitor LDN193189 on Ambystoma mexicanum to explore the role of BMPs in regeneration. We find that BMP signaling is required for proper expression of various patterning genes and that its inhibition causes major defects in the regenerated limbs. Fgf8 is downregulated when BMP signaling is blocked, but ectopic injection of either human or axolotl protein did not rescue the defects. By administering LDN193189 treatments at different time points during regeneration, we show clearly that limb regeneration progresses in a proximal to distal fashion. This demonstrates that BMPs play a major role in patterning of regenerated limbs and that regeneration is a progressive process like development.

A Neuroprotective Dose of Isatin Causes Multilevel Changes Involving the Brain Proteome: Prospects for Further Research

Isatin (indole-2,3-dione) is an endogenous regulator, exhibiting a wide range of biological and pharmacological activities. At doses of 100 mg/kg and above, isatin is neuroprotective in different experimental models of neurodegeneration. Good evidence exists that its effects are realized via interaction with numerous isatin-binding proteins identified in the brain and peripheral tissues studied. In this study, we investigated the effect of a single dose administration of isatin to mice (100 mg/kg, 24 h) on differentially expressed proteins and a profile of the isatin-binding proteins in brain hemispheres. Isatin administration to mice caused downregulation of 31 proteins. However, these changes cannot be attributed to altered expression of corresponding genes. Although at this time point isatin influenced the expression of more than 850 genes in brain hemispheres (including 433 upregulated and 418 downregulated genes), none of them could account for the changes in the differentially expressed proteins. Comparative proteomic analysis of brain isatin-binding proteins of control and isatin-treated mice revealed representative groups of proteins sensitive to isatin administration. Control-specific proteins (n = 55) represent specific targets that interact directly with isatin. Appearance of brain isatin-binding proteins specific to isatin-treated mice (n = 94) may be attributed to the formation of new clusters of protein–protein interactions and/or novel binding sites induced by a high concentration of this regulator (ligand-induced binding sites). Thus, isatin administration produces multiple effects in the brain, which include changes in gene expression and also profiles of isatin-binding proteins and their interactomes. Further studies are needed for deeper insight into the mechanisms of the multilevel changes in the brain proteome induced by isatin. In the context of the neuroprotective action, these changes may be aimed at interruption of pathological links that begin to form after initiation of pathological processes.

Nox4-mediated ROS production is involved, but not essential for TGFβ-induced lens EMT leading to cataract

The reactive oxygen species (ROS) producing enzyme, NADPH oxidase 4 (Nox4), is upregulated in response to TGFβ in lens epithelial cells in vitro, and its selective inhibition was shown to block aspects of TGFβ-induced epithelial-mesenchymal transition (EMT). In the present in situ study we validate the role(s) of Nox4 in TGFβ-induced lens EMT leading to anterior subcapsular cataract (ASC) formation. Mice overexpressing TGFβ in the lens, that develop ASC, were crossed to Nox4-deficient mice. When comparing mice overexpressing TGFβ in lens, to mice that were also deficient for Nox4, we see the delayed onset of cataract, along with a delay in EMT protein markers normally associated with TGFβ-induced fibrotic cataracts. In the absence of Nox4, we also see elevated levels of ERK1/2 activity that was shown to be required for TGFβ/Smad2/3-signaling. qRT-PCR revealed upregulation of Nox2 and its regulatory subunit in TGFβ-overexpressing lens epithelial cells devoid of Nox4. Taken together, these findings provide an improved platform to delineate putative Nox4 (and ROS) interactions with Smad2/3 and/or ERK1/2, in particular in the development of fibrotic diseases, such as specific forms of cataract.

Integrative Analysis of Axolotl Gene Expression Data from Regenerative and Wound Healing Limb Tissues

Axolotl (Ambystoma mexicanum) is a urodele amphibian endowed with remarkable regenerative capacities manifested in scarless wound healing and restoration of amputated limbs, which makes it a powerful experimental model for regenerative biology and medicine. Previous studies have utilized microarrays and RNA-Seq technologies for detecting differentially expressed (DE) genes in different phases of the axolotl limb regeneration. However, sufficient consistency may be lacking due to statistical limitations arising from intra-laboratory analyses. This study aims to bridge such gaps by performing an integrative analysis of publicly available microarray and RNA-Seq data from axolotl limb samples having comparable study designs using the "merging" method. A total of 351 genes were found DE in regenerative samples compared to the control in data of both technologies, showing an adjusted p-value < 0.01 and log fold change magnitudes >1. Downstream analyses illustrated consistent correlations of the directionality of DE genes within and between data of both technologies, as well as concordance with the literature on regeneration related biological processes. qRT-PCR analysis validated the observed expression level differences of five of the top DE genes. Future studies may benefit from the utilized concept and approach for enhanced statistical power and robust discovery of biomarkers of regeneration.

Modeling Progressive Fibrosis with Pluripotent Stem Cells Identifies an Anti-fibrotic Small Molecule

Progressive organ fibrosis accounts for one-third of all deaths worldwide, yet preclinical models that mimic the complex, progressive nature of the disease are lacking, and hence, there are no curative therapies. Progressive fibrosis across organs shares common cellular and molecular pathways involving chronic injury, inflammation, and aberrant repair resulting in deposition of extracellular matrix, organ remodeling, and ultimately organ failure. We describe the generation and characterization of an in vitro progressive fibrosis model that uses cell types derived from induced pluripotent stem cells. Our model produces endogenous activated transforming growth factor β (TGF-β) and contains activated fibroblastic aggregates that progressively increase in size and stiffness with activation of known fibrotic molecular and cellular changes. We used this model as a phenotypic drug discovery platform for modulators of fibrosis. We validated this platform by identifying a compound that promotes resolution of fibrosis in in vivo and ex vivo models of ocular and lung fibrosis.

TGF-β1 activates RSC96 Schwann cells migration and invasion through MMP-2 and MMP-9 activities

Following peripheral nerve injury, remnant Schwann cells adopt a migratory phenotype and remodel the extracellular matrix allowing axonal regrowth. Although much evidence has demonstrated that TGF-β1 promotes glioma cell motility and induces the expression of extracellular matrix proteins, the effects of TGF-β1 on Schwann cell migration has not yet been studied. We therefore investigated the cellular effects and the signal transduction pathways evoked by TGF-β1 in rattus norvegicus neuronal Schwann RSC96 cell. TGF-β1 significantly increased migration and invasion of Schwann cells assessed by the wound-healing assay and by cell invasion assay. TGF-β1-enhanced migration/invasion was blocked by inhibition of MMP-2 and MMP-9. Consistently, by real-time and western blot analyses, we demonstrated that TGF-β1 increased MMP-2 and MMP-9 mRNA and protein levels. TGF-β1 also increased MMPs activities in cell growth medium, as shown by gelatin zymography. The selective TGF-β Type I receptor inhibitor SB431542 completely abrogated any effects by TGF-β1. Indeed, TGF-β1 Type I receptor activation provoked the cytosol-to-nucleus translocation of SMAD2 and SMAD3. SMAD2 knockdown by siRNA blocked MMP-2 induction and cell migration/invasion due to TGF-β1. TGF-β1 also provoked phosphorylation of MAPKs extracellular regulated kinase 1/2 and JNK1/2. Both MAPKs were upstream to p65/NF-kB inasmuch as both MAPKs' inhibitors PD98059 and SP600125 or their down-regulation by siRNA significantly blocked the TGF-β1-induced nuclear translocation of p65/NF-kB. In addition, p65/NF-κB siRNA knockdown inhibited the effects of TGF-β1 on both MMP-9 and cell migration/invasion. We conclude that TGF-β1 controls RSC96 Schwann cell migration and invasion through MMP-2 and MMP-9 activities. MMP-2 is controlled by SMAD2 whilst MMP-9 is controlled via an ERK1/2-JNK1/2-NF-κB dependent pathway.

Role of TGF‑β in the motility of ShcD‑overexpressing 293 cells

The newly identified Src homology and collagen (Shc) family member ShcD was observed to be upregulated in 50% of vertical growth phase and metastatic melanomas. The aim of the present study was to investigate the mechanism by which ShcD mediates cell motility. 293 cell lines were altered to stably express GFP (GF) or GFP‑ShcD (G5). Treatment of the cells with transforming growth factor (TGF)β2 promoted extracellular signal‑regulated kinase (ERK) phosphorylation and, to a lesser extent, Smad2 phosphorylation in GFP‑ShcD‑expressing cells but not in GFP‑overexpressing cells. GFP‑ShcD‑expressing cells exhibited upregulated expression of certain epithelial‑mesenchymal transition‑related genes, such as snail family transcriptional repressor 1 and SLUG, than GFP‑expressing cells. Higher levels of ERK were found in the nuclear fraction of GFP‑ShcD‑expressing cells than that of GFP‑expressing cells. Overall, GFP‑ShcD‑expressing cells demonstrated enhanced migration compared with GFP‑expressing cells. A slight increase in cell migration was observed in both cell lines (GF and G5) when the cells were allowed to migrate towards conditioned medium derived from TGFβ2‑treated GFP‑ShcD expressing cells. Collectively, ShcD upregulation was proposed to induce cell migration by affecting the expression of certain epithelial‑mesenchymal transition‑related genes. Thus, our findings may improve understanding of the role of ShcD in cell migration.

Bioreactor-Controlled Physoxia Regulates TGF-β Signaling to Alter Extracellular Matrix Synthesis by Human Chondrocytes

Culturing articular chondrocytes under physiological oxygen tension exerts positive effects on their extracellular matrix synthesis. The underlying molecular mechanisms which enhance the chondrocytic phenotype are, however, still insufficiently elucidated. The TGF-β superfamily of growth factors, and the prototypic TGF-β isoforms in particular, are crucial in maintaining matrix homeostasis of these cells. We employed a feedback-controlled table-top bioreactor to investigate the role of TGF-β in microtissues of human chondrocytes over a wider range of physiological oxygen tensions (i.e., physoxia). We compared 1%, 2.5%, and 5% of partial oxygen pressure (pO₂) to the ‘normoxic’ 20%. We confirmed physoxic conditions through the induction of marker genes (PHD3, VEGF) and oxygen tension-dependent chondrocytic markers (SOX9, COL2A1). We identified 2.5% pO₂ as an oxygen tension optimally improving chondrocytic marker expression (ACAN, COL2A1), while suppressing de-differentiation markers (COL1A1,COL3A1). Expression of TGF-β isoform 2 (TGFB2) was, relatively, most responsive to 2.5% pO₂, while all three isoforms were induced by physoxia. We found TGF-β receptors ALK1 and ALK5 to be regulated by oxygen tension on the mRNA and protein level. In addition, expression of type III co-receptors betaglycan and endoglin appeared to be regulated by oxygen tension as well. R-Smad signaling confirmed that physoxia divergently regulated phosphorylation of Smad1/5/8 and Smad2/3. Pharmacological inhibition of canonical ALK5-mediated signaling abrogated physoxia-induced COL2A1 and PAI-1 expression. Physoxia altered expression of hypertrophy markers and that of matrix metalloproteases and their activity, as well as expression ratios of specific proteins (Sp)/Krüppel-like transcription factor family members SP1 and SP3, proving a molecular concept of ECM marker regulation. Keeping oxygen levels tightly balanced within a physiological range is important for optimal chondrocytic marker expression. Our study provides novel insights into transcriptional regulations in chondrocytes under physoxic in vitro conditions and may contribute to improving future cell-based articular cartilage repair strategies.

Kartogenin and Its Application in Regenerative Medicine

Regenerative medicine refers to the possibility of replacing aged/damaged cells with genetically similar young and functional cells to restore or establish normal function. Kartogenin (KGN), a small heterocyclic, drug-like compound was discovered in 2012, which is strongly associated with regenerative medicine. KGN has been applied in many regenerative fields, including cartilage regeneration and protection, tendon-bone healing, wound healing, and limb development. KGN could facilitate cartilage repair, promote formation of cartilage-like transition zone in tendon-bone junctions, stimulate collagen synthesis for wound healing, and regulate limb development in a coordinated manner. Considering the related mechanism, filamin A/CBFβ/RUNX1, Ihh, and TGFβ/Smad pathways have been reported to involve KGN. Therefore, KGN is proven a promising agent in regenerative medicine; however, studies conducted on the effect of KGN are limited to date and not convictive for long-term use. Further studies are recommended to explore the long-term effect and potential molecular mechanisms of KGN. Our investigations may motivate researchers to expand its applications in different forms and fields.

Epithelial to mesenchymal transition is mediated by both TGF-β canonical and non-canonical signaling during axolotl limb regeneration

Axolotls have the amazing ability to regenerate. When compared to humans, axolotls display a very fast wound closure, no scarring and are capable to replace lost appendages perfectly. Understanding the signaling mechanism leading to this perfect healing is a key step to help develop regenerative treatments for humans. In this paper, we studied cellular pathways leading to axolotl limb regeneration. We focus on the wound closure phase where keratinocytes migrate to close the lesion site and how epithelial to mesenchymal transitions are involved in this process. We observe a correlation between wound closure and EMT marker expression. Functional analyses using pharmacological inhibitors showed that the TGF-β/SMAD (canonical) and the TGF-β/p38/JNK (non-canonical) pathways play a role in the rate to which the keratinocytes can migrate. When we treat the animals with a combination of inhibitors blocking both canonical and non-canonical TGF-β pathways, it greatly reduced the rate of wound closure and had significant effects on certain known EMT genes.

Blastemal progenitors modulate immune signaling during early limb regeneration

Blastema formation, a hallmark of limb regeneration, requires proliferation and migration of progenitors to the amputation plane. Although blastema formation has been well described, the transcriptional programs that drive blastemal progenitors remain unknown. We transcriptionally profiled dividing and non-dividing cells in regenerating stump tissues, as well as the wound epidermis, during early axolotl limb regeneration. Our analysis revealed unique transcriptional signatures of early dividing cells and, unexpectedly, repression of several core developmental signaling pathways in early regenerating stump tissues. We further identify an immunomodulatory role for blastemal progenitors through interleukin 8 (IL-8), a highly expressed cytokine in subpopulations of early blastemal progenitors. Ectopic il-8 expression in non-regenerating limbs induced myeloid cell recruitment, while IL-8 knockdown resulted in defective myeloid cell retention during late wound healing, delaying regeneration. Furthermore, the il-8 receptor cxcr-1/2 was expressed in myeloid cells, and inhibition of CXCR-1/2 signaling during early stages of limb regeneration prevented regeneration. Altogether, our findings suggest that blastemal progenitors are active early mediators of immune support, and identify CXCR-1/2 signaling as an important immunomodulatory pathway during the initiation of regeneration.

Opposite effects of Activin type 2 receptor ligands on cardiomyocyte proliferation during development and repair

Zebrafish regenerate damaged myocardial tissue very effectively. Hence, insights into the molecular networks underlying zebrafish heart regeneration might help develop alternative strategies to restore human cardiac performance. While TGF-β signaling has been implicated in zebrafish cardiac regeneration, the role of its individual ligands remains unclear. Here, we report the opposing expression response during zebrafish heart regeneration of two genes, mstnb and inhbaa, which encode TGF-β family ligands. Using gain-of-function (GOF) and loss-of-function (LOF) approaches, we show that these ligands mediate inverse effects on cardiac regeneration and specifically on cardiomyocyte (CM) proliferation. Notably, we find that Inhbaa functions as a CM mitogen and that its overexpression leads to accelerated cardiac recovery and scar clearance after injury. In contrast, mstnb GOF and inhbaa LOF both lead to unresolved scarring after cardiac injury. We further show that Mstnb and Inhbaa inversely control Smad2 and Smad3 transcription factor activities through alternate Activin type 2 receptors.

Pseudotyped baculovirus is an effective gene expression tool for studying molecular function during axolotl limb regeneration

Axolotls can regenerate complex structures through recruitment and remodeling of cells within mature tissues. Accessing the underlying mechanisms at a molecular resolution is crucial to understand how injury triggers regeneration and how it proceeds. However, gene transformation in adult tissues can be challenging. Here we characterize the use of pseudotyped baculovirus (BV) as an effective gene transfer method both for cells within mature limb tissue and within the blastema. These cells remain competent to participate in regeneration after transduction. We further characterize the effectiveness of BV for gene overexpression studies by overexpressing Shh in the blastema, which yields a high penetrance of classic polydactyly phenotypes. Overall, our work establishes BV as a powerful tool to access gene function in axolotl limb regeneration.

Mice overexpressing growth hormone exhibit increased skeletal muscle myostatin and MuRF1 with attenuation of muscle mass

Background

In contrast to the acute effects of growth hormone (GH) on skeletal muscle protein synthesis, long-term GH treatment appears to have negligible effects on muscle mass. Despite this knowledge, little is known regarding the chronic effects of GH on skeletal muscle protein synthesis and atrophy signaling pathways. The purpose of this study was to determine if protein synthesis pathways are attenuated and/or muscle atrophy intracellular signaling pathways are altered in the skeletal muscle of transgenic bovine GH (bGH) mice.

Methods

The gastrocnemius and soleus from 5-month-old male bGH mice (n = 9) and wild type (WT) controls (n = 9) were harvested and analyzed for proteins involved in the protein synthesis (Akt/mTOR), growth and proliferation (MAPK), and muscle atrophy (MuRF1 and myostatin) pathways.

Results

Total body mass was significantly increased in bGH mice compared to WT controls (49%, P < 0.0001). When expressed relative to total body mass, the gastrocnemius (− 28%, P < 0.0001), but not the soleus, was significantly lower in mice overexpressing GH, compared to controls. Transgenic bGH mice had elevated phosphorylation levels of protein kinase b (Akt1), 4E-binding protein 1 (4E-BP1), p70 S6 kinase, p42/44, and p38 (P < 0.05) compared to WT littermates. Mature myostatin (26 kDa), premature myostatin (52 kDa), and activin receptor type IIB (AcvR2B) protein levels were increased in bGH mice (P < 0.05), along with elevated phosphorylation levels of mothers against decapentaplegic homolog (Smad2) (59%, P < 0.0001). Mice overexpressing GH had increased MuRF1 expression (30%, P < 0.05) and insulin receptor substrate 1 (IRS1) serine phosphorylation (44%, P < 0.05) in the gastrocnemius, but not the soleus, when compared to controls.

Conclusions

These findings demonstrate that chronic elevations in circulating GH have a critical impact on signaling pathways involved in skeletal muscle protein synthesis and atrophy, and suggest that MuRF1, myostatin, and IRS1 serine phosphorylation may act to inhibit exaggerated glycolytic muscle growth, in environments of chronic GH/IGF-1 excess.

Advances in Decoding Axolotl Limb Regeneration

Humans and other mammals are limited in their natural abilities to regenerate lost body parts. By contrast, many salamanders are highly regenerative and can spontaneously replace lost limbs even as adults. Because salamander limbs are anatomically similar to human limbs, knowing how they regenerate should provide important clues for regenerative medicine. Although interest in understanding the mechanics of this process has never wavered, until recently researchers have been vexed by seemingly impenetrable logistics of working with these creatures at a molecular level. Chief among the problems has been the very large size of salamander genomes, and not a single salamander genome has been fully sequenced to date. Recently the enormous gap in sequence information has been bridged by approaches that leverage mRNA as the starting point. Together with functional experimentation, these data are rapidly enabling researchers to finally uncover the molecular mechanisms underpinning the astonishing biological process of limb regeneration.