The effects of DNA methyltransferase inhibitors and histone deacetylase inhibitors on digit regeneration in mice

Epigenetic regulation of macrophage polarization in wound healing

The immune microenvironment plays a critical role in regulating skin wound healing. Macrophages, the main component of infiltrating inflammatory cells, play a pivotal role in shaping the immune microenvironment in the process of skin wound healing. Macrophages comprise the classic proinflammatory M1 subtype and anti-inflammatory M2 population. In the early inflammatory phase of skin wound closure, M1-like macrophages initiate and amplify the local inflammatory response to disinfect the injured tissue. In the late tissue-repairing phase, M2 macrophages are predominant in wound tissue and limit local inflammation to promote tissue repair. The biological function of macrophages is tightly linked with epigenomic organization. Transcription factors are essential for macrophage polarization. Epigenetic modification of transcription factors determines the heterogeneity of macrophages. In contrast, transcription factors also regulate the expression of epigenetic enzymes. Both transcription factors and epigenetic enzymes form a complex network that regulates the plasticity of macrophages. Here, we describe the latest knowledge concerning the potential epigenetic mechanisms that precisely regulate the biological function of macrophages and their effects on skin wound healing.

SUV39H1 regulates corneal epithelial wound healing via H3K9me3-mediated repression of p27

Background

Corneal epithelial wound healing (CEWH) is vital for maintaining the integrity and barrier function of the cornea. Although histone modifications mediating gene expression patterns is fundamental in some other tissues, it remains unclear whether these gene regulation patterns underlie CEWH. Suppressor of variegation 3-9 homolog 1 (SUV39H1) plays a vital role in mediating gene silencing via histone H3 trimethylation of lysine 9 (H3K9me3). This study aims to characterize the comprehensive signature of epigenetic modifiers and determine the role of SUV39H1 in CEWH.

Methods

NanoString nCounter technology was used to detect the differentially expressed epigenetic modifiers during CEWH. Bioinformatic analyses were performed to reveal their involvement in this process. After knockdown of SUV39H1 with siRNA transfection, we determined the function of SUV39H1 on cell proliferation and migration in human corneal epithelial cells (HCECs) via MTS, EdU, and wound-healing assay, respectively. Flow cytometry analysis further confirmed the effect of SUV39H1 on the cell cycle of HCECs. Loss-of-function assays for SUV39H1 with siRNA injection or chaetocin assessed the role of SUV39H1 on CEWH in vivo. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blotting characterized the expression of SUV39H1 and its target genes. Chromatin immunoprecipitation assay was used to evaluate the distributions of H3K9me3 marks at the promoters of SUV39H1 target genes.

Results

We first identified 92 differentially expressed epigenetic modifiers and revealed their involvement during CEWH. SUV39H1 was confirmed to be upregulated in response to corneal injury. Its downregulation significantly inhibited HCEC proliferation and retarded in vivo CEWH. Furthermore, knockdown of SUV39H1 upregulated the p27 expression level and reduced H3K9me3 marks at p27 promoter in HCECs. In addition, p27 was remarkably downregulated with elevated H3K9me3 marks at its promoter during in vivo CEWH.

Conclusions

SUV39H1 plays a critical role in regulating corneal epithelial cell proliferation via H3K9me3-mediated suppression of p27 during CEWH. Our findings suggest that epigenetic modifiers such as SUV39H1 can be potential therapeutic approaches to accelerate corneal repair.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40662-022-00275-5.

A ZFP42/MARK2 regulatory network reduces the damage of retinal ganglion cells in glaucoma: a study based on GEO dataset and in vitro experiments

Glaucoma is a common disorder in which the death of retinal ganglion cells (RGCs) results in a progressive loss of sight, even blindness. This study was performed to reveal the key molecular mechanism of RGC damage in glaucoma based on the Gene Expression Omnibus database. Glaucoma-related microarray datasets were identified, followed by collection of differentially expressed genes (DEGs) with the key genes discovered by weighted gene co-expression network analysis. Through LASSO regression analysis, candidate genes involved in the pathogenesis of glaucoma were identified with their accuracy evaluated by receiver operating characteristic curve analysis. The glaucoma-specific transcriptional regulatory network was constructed to determine the key transcription factor regulatory axis. Then, in vitro cell models were established using H₂O₂ for further verifying the regulatory role of identified ZFP42/MARK2 axis in RGC damage in glaucoma. Differential analysis of GSE27276, GSE45570, and GSE101727 microarray datasets yielded 165 DEGs, and 22 key genes were identified following. Then, 9 candidate genes involved in the pathogenesis of glaucoma was collected and the key ZFP42/MARK2 regulatory axis was found. In vitro cell experiments further confirmed that ZFP42 and MARK2 were down-regulated in RGCs treated with H₂O₂. In addition, overexpression of ZFP42 increased the expression of MARK2 to increase RGC cell viability, and reduce cell apoptosis and ROS levels, while silencing MARK2 could reverse the protective effect of ZFP42. We confirmed that ZFP42 reduced the damage of RGCs in glaucoma by up-regulating the expression of MARK2.

TIP60 acts as a regulator of genes involved in filopodia formation and cell migration during wound healing

Wound healing is a complex phenomenon that requires coordination of numerous molecular and cellular changes to facilitate timely and efficient repair of the damaged tissue. Although many of these molecular pathways have been detailed, others remain to be elucidated. In the present work, we show for the first time, roles for the acetyltransferase TIP60 and nuclear receptor transcription factor PXR in this process, participating in wound healing by altering actin dynamics and cellular motility. We found that in response to wound-injury, TIP60 induces rapid formation of filopodia at the wounded cell front, leading to enhanced cell migration and faster closure of the wound. Further, qPCR analysis revealed heightened expression of Cdc42 and ROCK1 genes, key regulators involved in filopodia formation and actin reorganization, exclusively in TIP60-PXR-expressing cells upon wound-induction. We also performed ChIP assays to confirm the context-specific binding of TIP60 on the ROCK1 promoter and demonstrated that the TIP60 chromodomain is essential for loading of the TIP60–PXR complex onto the chromatin. Results from immunoprecipitation assays revealed that during the wounded condition, TIP60 alters the chromatin microenvironment by specifically acetylating histones H2B and H4, thereby modulating the expression of target genes. Overall, findings of this study show that TIP60 is a novel regulator of the wound healing process by regulating the expression of wound repair-related genes.

Photobiomodulation therapy drives massive epigenetic histone modifications, stem cells mobilization and accelerated epithelial healing

Emerging evidence indicates the clinical benefits of photobiomodulation therapy (PBMT) in the management of skin and mucosal wounds. Here, we decided to explore the effects of different regiments of PBMT on epithelial cells and stem cells, and the potential implications over the epigenetic circuitry during healing. Scratch-wound migration, immunofluorescence (anti-acetyl-Histone H3, anti-acetyl-CBP/p300 and anti-BMI1), nuclear morphometry and western blotting (anti-Phospho-S6, anti-methyl-CpG binding domain protein 2 [MBD2]) were performed. Epithelial stem cells were identified by the aldehyde dehydrogenase enzymatic levels and sphere-forming assay. We observed that PBMT-induced accelerated epithelial migration and chromatin relaxation along with increased levels of histones acetylation, the transcription cofactors CBP/p300 and mammalian target of rapamycin. We further observed a reduction of the transcription repression-associated protein MBD2 and a reduced number of epithelial stem cells and spheres. In this study, we showed that PBMT could induce epigenetic modifications of epithelial cells and control stem cell fate, leading to an accelerated healing phenotype.

Histone Acetylation as a Regenerative Target in the Dentine-Pulp Complex

If dental caries (or tooth decay) progresses without intervention, the infection will advance through the dentine leading to severe pulpal inflammation (irreversible pulpitis) and pulp death. The current management of irreversible pulpits is generally root-canal-treatment (RCT), a destructive, expensive, and often unnecessary procedure, as removal of the injurious stimulus alone creates an environment in which pulp regeneration may be possible. Current dental-restorative-materials stimulate repair non-specifically and have practical limitations; as a result, opportunities exist for the development of novel therapeutic strategies to regenerate the damaged dentine-pulp complex. Recently, epigenetic modification of DNA-associated histone ‘tails’ has been demonstrated to regulate the self-renewal and differentiation potential of dental-stem-cell (DSC) populations central to regenerative endodontic treatments. As a result, the activities of histone deacetylases (HDAC) are being recognised as important regulators of mineralisation in both tooth development and dental-pulp-repair processes, with HDAC-inhibition (HDACi) promoting pulp cell mineralisation in vitro and in vivo. Low concentration HDACi-application can promote de-differentiation of DSC populations and conversely, increase differentiation and accelerate mineralisation in DSC populations. Therapeutically, various HDACi solutions can release bioactive dentine-matrix-components (DMCs) from the tooth’s extracellular matrix; solubilised DMCs are rich in growth factors and can stimulate regenerative processes such as angiogenesis, neurogenesis, and mineralisation. The aim of this mini-review is to discuss the role of histone-acetylation in the regulation of DSC populations, while highlighting the importance of HDAC in tooth development and dental pulp regenerative-mineralisation processes, before considering the potential therapeutic application of HDACi in targeted biomaterials to the damaged pulp to stimulate regeneration.

Nerve-mediated expression of histone deacetylases regulates limb regeneration in axolotls

Axolotls have amazing abilities to regenerate their lost limbs. Nerve and wound epidermis have great impacts on this regeneration. Histone deacetylases (HDACs) have been shown to play roles in the regeneration of amphibian tails and limbs. In this study, a bi-phasic up-regulation of HDAC1 was noted before early differentiation stage of axolotl limb regeneration. Limb regeneration was delayed in larvae incubated with an HDAC inhibitor MS-275. Local injection of MS-275 or TSA, another HDAC inhibitor, into amputation sites of the juveniles did not interfere with wound healing but more profoundly inhibited local HDAC activities and blastema formation/limb regeneration. Elevation of HDAC1 expression was more apparent in wound epidermis than in mesenchyme. Prior denervation prohibited this elevation and limb regeneration. Supplementation of nerve factors BMP7, FGF2, and FGF8 in the stump ends after amputation on denervated limbs not only enabled HDAC1 up-regulation but also led to more extent of limb regeneration. In conclusion, nerve-mediated HDAC1 expression is required for blastema formation and limb regeneration.

Epigenetic Approaches to the Treatment of Dental Pulp Inflammation and Repair: Opportunities and Obstacles

Concerns over the cost and destructive nature of dental treatment have led to the call for novel minimally invasive, biologically based restorative solutions. For patients with toothache, this has resulted in a shift from invasive root-canal-treatment (RCT) toward more conservative vital-pulp-treatment (VPT) procedures, aimed to protect the pulp and harness its natural regenerative capacity. If the dental pulp is exposed, as long as the infection and inflammation can be controlled, conservative therapies can promote the formation of new tertiary dentine in a stem cell-led reparative process. Crucially, the volume and quality of new dentine is dependent on the material applied; however, currently available dental-materials are limited by non-specific action, cytotoxicity and poor clinical handling. Looking to the future, an improved understanding of the cellular regulators of pulpal inflammation and associated repair mechanisms is critical to predict pulpal responses and devise novel treatment strategies. Epigenetic modifications of DNA-associated proteins and the influences of non-coding RNAs have been demonstrated to control the self-renewal of stem cell populations as well as regulate mineralised tissue development and repair. Notably, the stability of microRNAs and their relative ease of sampling from pulpal blood highlight their potential for application as diagnostic inflammatory biomarkers, while increased understanding of their actions will not only enhance our knowledge of pulpal disease and repair, but also identify novel molecular targets. The potential therapeutic application of epigenetic modifying agents, DNA-methyltransferase-inhibitors (DNMTi) and histone-deacetylase-inhibitors (HDACi), have been shown to promote mineralisation and repair processes in dental-pulp-cell (DPC) populations as well as induce the release of bioactive dentine-matrix-components. Consequently, HDACis and DNMTis have the potential to enhance tertiary dentinogenesis by influencing the cellular and tissue processes at low concentrations with minimal side effects, providing an opportunity to develop a topically placed, inexpensive bio-inductive restorative material. The aim of this review is to highlight the potential role of epigenetic approaches in the treatment of the damaged dental pulp, considering the opportunities and obstacles, such as off-target effects, delivery mechanisms, for the therapeutic use of miRNA as an inflammatory biomarker or molecular target, before discussing the application of HDACi and DNMTi to the damaged pulp to stimulate repair.

Effects of the led therapy on the global DNA methylation and the expression of Dnmt1 and Dnmt3a genes in a rat model of skin wound healing

The use of light emitting diodes (LED) as a therapeutic resource for wound healing has increased over the last years; however, little is still known about the molecular pathways associated to LED exposure. In the present study, we verified the effects of LED therapy on DNA methylation and expression of the DNA methyltransferase (Dnmt) genes, Dnmt1 and Dnmt3a, in an in vivo model of epithelial wound healing. Male Wistar rats were submitted to epithelial excision in the dorsal region and subsequently distributed within the experimental groups: group 1, animals that received irradiation of 0.8 J/cm(2) of LED (604 nm); group 2, animals that received 1.6 J/cm(2) of LED (604 nm); control (CTL), animals not submitted to therapeutic intervention. LED applications were performed during 7 days, and tissues from the periphery of the wound area were obtained for molecular analysis. The Image-J software was used for analysis of the wound area. DNA methylation was evaluated by ELISA-based method and gene expressions were quantified by real-time PCR. Decrease on global DNA methylation profile was observed in all experimental groups (CTL, 1, and 2) revealing the participation of DNA methylation in the healing process. Significant decrease in the wound area accompanied by increase in the Dnmt3a expression was associated to group 2. Based on our findings, we propose that DNA methylation is an important molecular mechanism associated to wound healing and that irradiation with 1.6 J/cm(2) of LED evokes an increase in the expression of the Dnmt3a that might associates to the efficiency of the epithelial wound healing.

Transition from inflammation to proliferation: a critical step during wound healing

The ability to rapidly restore the integrity of a broken skin barrier is critical and is the ultimate goal of therapies for hard-to-heal-ulcers. Unfortunately effective treatments to enhance healing and reduce scarring are still lacking. A deeper understanding of the physiology of normal repair and of the pathology of delayed healing is a prerequisite for the development of more effective therapeutic interventions. Transition from the inflammatory to the proliferative phase is a key step during healing and accumulating evidence associates a compromised transition with wound healing disorders. Thus, targeting factors that impact this phase transition may offer a rationale for therapeutic development. This review summarizes mechanisms regulating the inflammation-proliferation transition at cellular and molecular levels. We propose that identification of such mechanisms will reveal promising targets for development of more effective therapies.

MSCs: The Sentinel and Safe-Guards of Injury

Mesenchymal stem cells (MSCs) were originally named because they could differentiate in a variety of mesenchymal phenotypes in culture. Evidence indicates that MSCs arise from perivascular cells, pericytes, when the blood vessels are broken or inflamed. These pericyte/MSCs are situated on every blood vessel in the body. The MSCs sense the micro-environment of the injury site and secrete site-specific factors that serve several important reparative functions: first, a curtain of molecules from the front of the MSCs provide a barrier from the interrogation of the over-aggressive immune system. Second, from the back of the MSCs, a different set of bioactive agents inhibit scar formation and establish a regenerative micro-environment. Third, if bacteria are sensed by the MSCs, they produce powerful protein antibiotics that kill the bacteria on contact. Last, the MSCs surround and encyst intruding solid objects like a piece of wood (a "splinter") or other foreign objects. The MSCs act as a combination paramedic and emergency room (ER) staff to survey the damage, isolate foreign components, stabilize the injured tissues, provide antibiotics and encysting protection before a slower, medicinal sequence can be initiated to regenerate the damaged tissue. The MSCs, thus, act as sentinels to safeguard the individual from intrusion and chronic injury. A societal treatment system has evolved, paramedics and ER procedures, which mirror in a macro-sense what MSCs orchestrate in a micro-sense. Key to this new understanding is that MSCs are not "stem cells," but rather as Medicinal Signaling Cells as the therapeutic agents.

Epigenetic modulation of dental pulp stem cells: implications for regenerative endodontics

Dental pulp stem cells (DPSCs) offer significant potential for use in regenerative endodontics, and therefore, identifying cellular regulators that control stem cell fate is critical to devising novel treatment strategies. Stem cell lineage commitment and differentiation are regulated by an intricate range of host and environmental factors of which epigenetic influence is considered vital. Epigenetic modification of DNA and DNA-associated histone proteins has been demonstrated to control cell phenotype and regulate the renewal and pluripotency of stem cell populations. The activities of the nuclear enzymes, histone deacetylases, are increasingly being recognized as potential targets for pharmacologically inducing stem cell differentiation and dedifferentiation. Depending on cell maturity and niche in vitro, low concentration histone deacetylase inhibitor (HDACi) application can promote dedifferentiation of several post-natal and mouse embryonic stem cell populations and conversely increase differentiation and accelerate mineralization in DPSC populations, whilst animal studies have shown an HDACi-induced increase in stem cell marker expression during organ regeneration. Notably, both HDAC and DNA methyltransferase inhibitors have also been demonstrated to dramatically increase the reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) for use in regenerative therapeutic procedures. As the regulation of cell fate will likely remain the subject of intense future research activity, this review aims to describe the current knowledge relating to stem cell epigenetic modification, focusing on the role of HDACi on alteration of DPSC phenotype, whilst presenting the potential for therapeutic application as part of regenerative endodontic regimens.

The Epigenetic Regulation of Wound Healing

Significance: Epigenetic regulatory mechanisms are essential for epidermal homeostasis and contribute to the pathogenesis of many skin diseases, including skin cancer and psoriasis. However, while the epigenetic regulation of epidermal homeostasis is now becoming active area of research, the epigenetic mechanisms controlling the wound healing response remain relatively untouched. Recent Advances: Substantial progress achieved within the last two decades in understanding epigenetic mechanisms controlling gene expression allowed defining several levels, including covalent DNA and histone modifications, ATP-dependent and higher-order chromatin chromatin remodeling, as well as noncoding RNA- and microRNA-dependent regulation. Research pertained over the last few years suggests that epigenetic regulatory mechanisms play a pivotal role in the regulation of skin regeneration and control an execution of reparative gene expression programs in both skin epithelium and mesenchyme. Critical Issues: Epigenetic regulators appear to be inherently involved in the processes of skin repair, and are able to dynamically regulate keratinocyte proliferation, differentiation, and migration, together with influencing dermal regeneration and neoangiogenesis. This is achieved through a series of complex regulatory mechanisms that are able to both stimulate and repress gene activation to transiently alter cellular phenotype and behavior, and interact with growth factor activity. Future Directions: Understanding the molecular basis of epigenetic regulation is a priority as it represents potential therapeutic targets for the treatment of both acute and chronic skin conditions. Future research is, therefore, imperative to help distinguish epigenetic modulating drugs that can be used to improve wound healing.

Restitutio ad integrum: a dream or a real possibility?

The subject of organ regeneration has attracted substantial investigative attention and has been extensively reviewed. Therefore, I shall focus on several only recently emerged issues and on those aspects of stem cell-mediated regeneration which, although are important in my opinion, have nevertheless evaded the radar of scientific pursuit. Specifically, I shall describe the recent work on the prominence of local lineage-restricted stem cells, as opposed to the bone marrow-derived or circulating ones, in regeneration. This will be followed by an attempt to re-interpret a bulk of published data on the beneficial effects of cell therapy with the focus on the secretome of stem cells. Multiple factors that conspire to cause insufficient or failed regeneration in adult mammals will be screened with emphasis placed on the mechanical forces, senescence and exhaustion, each leading to phenotypical switch and/or stem cell incompetence. Finally, I shall enumerate several potential pathways to induce or restore stem cell competence. Although a significant amount of work has been performed in the non-renal field, I would hope that some of the mechanisms and concepts discussed herein will eventually trickle into kidney regeneration.

Histone deacetylase inhibitor enhances recovery after AKI

At present, there are no effective therapies to ameliorate injury, accelerate recovery, or prevent postinjury fibrosis after AKI. Here, we sought to identify candidate compounds that accelerate recovery after AKI by screening for small molecules that increase proliferation of renal progenitor cells in zebrafish embryos. One compound identified from this screen was the histone deacetylase inhibitor methyl-4-(phenylthio)butanoate, which we subsequently administered to zebrafish larvae and mice 24-48 hours after inducing AKI. In zebrafish, treatment with the compound increased larval survival and proliferation of renal tubular epithelial cells. In mice, treatment accelerated recovery, reduced postinjury tubular atrophy and interstitial fibrosis, and increased the regenerative capacity of actively cycling renal tubular cells by decreasing the number of cells in G2/M arrest. These data suggest that accelerating recovery may be a viable approach to treating AKI and provide proof of concept that a screen in zebrafish embryos can identify therapeutic candidates for kidney injury.

BMP2 induces segment-specific skeletal regeneration from digit and limb amputations by establishing a new endochondral ossification center

Bone morphogenetic proteins (BMPs) are required for bone development, the repair of damage skeletal tissue, and the regeneration of the mouse digit tip. Previously we showed that BMP treatment can induce a regeneration response in mouse digits amputated at a proximal level of the terminal phalangeal element (P3) (Yu et al., 2010). In this study, we show that the regeneration-inductive ability of BMP2 extends to amputations at the level of the second phalangeal element (P2) of neonatal digits, and the hindlimb of adult limbs. In these models the induced regenerative response is restricted in a segment-specific manner, thus amputated skeletal elements regenerate distally patterned skeletal structures but does not form joints or more distal skeletal elements. Studies on P2 amputations indicate that BMP2-induced regeneration is associated with a localized proliferative response and the transient expression of established digit blastema marker genes. This is followed by the formation of a new endochondral ossification center at the distal end of the bone stump. The endochondral ossification center contains proliferating chondrocytes that establish a distal proliferative zone and differentiate proximally into hypertrophic chondrocytes. Skeletal regeneration occurs from proximal to distal with the appearance of osteoblasts that differentiate in continuity with the amputated stump. Using the polarity of the endochondral ossification centers induced by BMP2 at two different amputation levels, we show that BMP2 activates a level-dependent regenerative response indicative of a positional information network. In summary, our studies provide evidence that BMP2 induces the regeneration of mammalian limb structures by stimulating a new endochondral ossification center that utilizes an existing network of positional information to regulate patterning during skeletal regeneration.

Emerging roles for retinoids in regeneration and differentiation in normal and disease states

The vitamin A (retinol) metabolite, all-trans retinoic acid (RA), is a signaling molecule that plays key roles in the development of the body plan and induces the differentiation of many types of cells. In this review the physiological and pathophysiological roles of retinoids (retinol and related metabolites) in mature animals are discussed. Both in the developing embryo and in the adult, RA signaling via combinatorial Hox gene expression is important for cell positional memory. The genes that require RA for the maturation/differentiation of T cells are only beginning to be cataloged, but it is clear that retinoids play a major role in expression of key genes in the immune system. An exciting, recent publication in regeneration research shows that ALDH1a2 (RALDH2), which is the rate-limiting enzyme in the production of RA from retinaldehyde, is highly induced shortly after amputation in the regenerating heart, adult fin, and larval fin in zebrafish. Thus, local generation of RA presumably plays a key role in fin formation during both embryogenesis and in fin regeneration. HIV transgenic mice and human patients with HIV-associated kidney disease exhibit a profound reduction in the level of RARβ protein in the glomeruli, and HIV transgenic mice show reduced retinol dehydrogenase levels, concomitant with a greater than 3-fold reduction in endogenous RA levels in the glomeruli. Levels of endogenous retinoids (those synthesized from retinol within cells) are altered in many different diseases in the lung, kidney, and central nervous system, contributing to pathophysiology. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.

Rex1 (Zfp42) null mice show impaired testicular function, abnormal testis morphology, and aberrant gene expression

Rex1 (Zfp42), GeneID 132625, is a gene whose expression is closely associated with pluripotency/multipotency in both mouse and human embryonic stem cells. To study the function of the murine Rex1 gene in vivo, we have used cre/lox technology to create Rex1(floxed) mice and mice deficient in Rex1 gene function. Rex1(-/-)males are characterized by an age-associated decrease in sperm counts, abnormal sperm morphology, and mild testicular atrophy. We characterized global patterns of gene expression in primary germ cells by microarray and identified the growth hormone responsive gene, GRTP1, as a transcript present at a 4.5 fold higher level in wild type (WT) compared to Rex1(-/-) mice. We analyzed immature germ cell (Dazl), proliferating (PCNA), and Sertoli cell populations, and quantitated levels of apoptosis in Rex1(-/-) as compared to WT testes. We evaluated the expression of proteins previously reported to correlate with Rex1 expression, such as STAT3, phospho-STAT3, p38, and phospho-p38 in the testis. We report a distinct cellular localization of total STAT3 protein in Rex1(-/-) affected testes. Our data suggest that loss of Rex1 leads to impaired testicular function.

HDACi

Acetylation of histone and non-histone proteins alters gene expression and induces a host of cellular effects. The acetylation process is homeostatically balanced by two groups of cellular enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs). HAT activity relaxes the structure of the human chromatin, rendering it transcriptionally active, thereby increasing gene expression. In contrast, HDAC activity leads to gene silencing. The enzymatic balance can be ‘tipped’ by histone deacetylase inhibitors (HDACi), leading to an accumulation of acetylated proteins, which subsequently modify cellular processes including stem cell differentiation, cell cycle, apoptosis, gene expression, and angiogenesis. There is a variety of natural and synthetic HDACi available, and their pleiotropic effects have contributed to diverse clinical applications, not only in cancer but also in non-cancer areas, such as chronic inflammatory disease, bone engineering, and neurodegenerative disease. Indeed, it appears that HDACi-modulated effects may differ between ‘normal’ and transformed cells, particularly with regard to reactive oxygen species accumulation, apoptosis, proliferation, and cell cycle arrest. The potential beneficial effects of HDACi for health, resulting from their ability to regulate global gene expression by epigenetic modification of DNA-associated proteins, also offer potential for application within restorative dentistry, where they may promote dental tissue regeneration following pulpal damage.

Wound healing and blastema formation in regenerating digit tips of adult mice

Amputation of the distal region of the terminal phalanx of mice causes an initial wound healing response followed by blastema formation and the regeneration of the digit tip. Thus far, most regeneration studies have focused in embryonic or neonatal models and few studies have examined adult digit regeneration. Here we report on studies that include morphological, immunohistological, and volumetric analyses of adult digit regeneration stages. The regenerated digit is grossly similar to the original, but is not a perfect replacement. Re-differentiation of the digit tip occurs by intramembranous ossification forming a trabecular bone network that replaces the amputated cortical bone. The digit blastema is comprised of proliferating cells that express vimentin, a general mesenchymal marker, and by comparison to mature tissues, contains fewer endothelial cells indicative of reduced vascularity. The majority of blastemal cells expressing the stem cell marker SCA-1, also co-express the endothelial marker CD31, suggesting the presence of endothelial progenitor cells. Epidermal closure during wound healing is very slow and is characterized by a failure of the wound epidermis to close across amputated bone. Instead, the wound healing phase is associated with an osteoclast response that degrades the stump bone allowing the wound epidermis to undercut the distal bone resulting in a novel re-amputation response. Thus, the regeneration process initiates from a level that is proximal to the original plane of amputation.

Extracellular matrix-derived products modulate endothelial and progenitor cell migration and proliferation in vitro and stimulate regenerative healing in vivo

Most adult mammals heal without restorative replacement of lost tissue and instead form scar tissue at an injury site. One exception is the adult MRL/MpJ mouse that can regenerate ear and cardiac tissue after wounding with little evidence of scar tissue formation. Following production of a MRL mouse ear hole, 2mm in diameter, a structure rapidly forms at the injury site that resembles the amphibian blastema at a limb amputation site during limb regeneration. We have isolated MRL blastemal cells (MRL-B) from this structure and adapted them to culture. We demonstrate by RT-PCR that even after continuous culturing of these cells they maintain expression of several progenitor cell markers, including DLK (Pref-1), and Msx-1. We have isolated the underlying extracellular matrix (ECM) produced by these MRL-B cells using a new non-proteolytic method and studied the biological activities of this cell-free ECM. Multiplex microELISA analysis of MRL-B cell-free ECM vs. cells revealed selective enrichment of growth factors such as bFGF, HGF and KGF in the matrix compartment. The cell-free ECM, degraded by mild enzyme treatment, was active in promoting migration and proliferation of progenitor cells in vitro and accelerating wound closure in a mouse full thickness cutaneous wound assay in vivo. In vivo, a single application of MRL-B cell matrix-derived products to full thickness cutaneous wounds in non-regenerative mice, B6, induced re-growth of pigmented hair, dermis and epidermis at the wound site whereas scar tissue replaced these tissues at wound sites in mice treated with vehicle alone. These studies suggest that matrix-derived products can stimulate regenerative healing and avert scar tissue formation in adult mammals.