Loss of epithelial hypoxia-inducible factor prolyl hydroxylase 2 accelerates skin wound healing in mice

PHD1-3 oxygen sensors in vivo-lessons learned from gene deletions

Oxygen sensors enable cells to adapt to limited oxygen availability (hypoxia), affecting various cellular and tissue responses. Prolyl-4-hydroxylase domain 1-3 (PHD1-3; also called Egln1-3, HIF-P4H 1-3, HIF-PH 1-3) proteins belong to the Fe2+- and 2-oxoglutarate-dependent dioxygenase superfamily and utilise molecular oxygen (O2) alongside 2-oxoglutarate as co-substrate to hydroxylate two proline residues of α subunits of the dimeric hypoxia inducible factor (HIF) transcription factor. PHD1-3-mediated hydroxylation of HIF-α leads to its degradation and inactivation. Recently, various PHD inhibitors (PHI) have entered the clinics for treatment of renal anaemia. Pre-clinical analyses indicate that PHI treatment may also be beneficial in numerous other hypoxia-associated diseases. Nonetheless, the underlying molecular mechanisms of the observed protective effects of PHIs are only partly understood, currently hindering their translation into the clinics. Moreover, the PHI-mediated increase of Epo levels is not beneficial in all hypoxia-associated diseases and PHD-selective inhibition may be advantageous. Here, we summarise the current knowledge about the relevance and function of each of the three PHD isoforms in vivo, based on the deletion or RNA interference-mediated knockdown of each single corresponding gene in rodents. This information is crucial for our understanding of the physiological relevance and function of the PHDs as well as for elucidating their individual impact on hypoxia-associated diseases. Furthermore, this knowledge highlights which diseases may best be targeted by PHD isoform-selective inhibitors in case such pharmacologic substances become available.

Transcriptomic analysis reveals that non-forage or forage fiber source promotes rumen development through different metabolic processes in lambs

Dietary fiber supplementation can stimulate rumen development in lambs during the pre-weaning period. However, it is unclear whether different sources of fiber have varying effects on rumen development. This study aimed to investigate the molecular mechanism of rumen morphological and functional development based on non-forage or forage as a starter dietary fiber source. Twenty-four male Hu lambs with similar body weights (BW, 3.67 ± 0.08 kg) were selected and divided into two groups that received diets supplemented with either alfalfa hay (AH) or soybean hull (SH). At the age of 70 days, six lambs were slaughtered from each treatment group for rumen fermentation and morphological analyses. Three samples of the rumen tissue from the ventral sac were collected for transcriptomic analysis. The results identified 633 differentially expressed genes (DEGs), of which 210 were upregulated and 423 were downregulated in the SH group compared with those in the AH group. The upregulated DEGs were most enriched in the immune function and proteolysis pathways, whereas the downregulated DEGs were mainly involved in cell proliferation, apoptosis, and differentiation pathways. These findings indicated that non-forage as a starter dietary fiber source improved immune function and enhanced nitrogen utilization, whereas forage facilitated rumen morphological development.

Hypoxia in Skin Cancer: Molecular Basis and Clinical Implications

Skin cancer is one of the most prevalent cancers in the Caucasian population. In the United States, it is estimated that at least one in five people will develop skin cancer in their lifetime, leading to significant morbidity and a healthcare burden. Skin cancer mainly arises from cells in the epidermal layer of the skin, where oxygen is scarce. There are three main types of skin cancer: malignant melanoma, basal cell carcinoma, and squamous cell carcinoma. Accumulating evidence has revealed a critical role for hypoxia in the development and progression of these dermatologic malignancies. In this review, we discuss the role of hypoxia in treating and reconstructing skin cancers. We will summarize the molecular basis of hypoxia signaling pathways in relation to the major genetic variations of skin cancer.

Reciprocal role of PLAP-1 in HIF-1α-mediated responses to hypoxia

OBJECTIVE

To investigate the mutual regulation of hypoxia-inducible factor (HIF)-1α activity and periodontal ligament-associated protein-1 (PLAP-1) expression in human periodontal ligament cells (HPDLs).

BACKGROUND

Cellular responses to hypoxia regulate various biological events (e.g., inflammation and tissue regeneration) through activation of HIF-1α. PLAP-1, an extracellular matrix protein preferentially expressed in the periodontal ligament, plays important roles in the functions of HPDLs. Although PLAP-1 expression has been demonstrated in hypoxic regions, the involvement of PLAP-1 in responses to hypoxia has not been revealed.

METHODS

HPDLs were cultured under normoxic (20% O₂ ) or hypoxic (1% O₂ ) conditions with or without deferoxamine mesylate (chemical hypoxia inducer) or chetomin (HIF signaling inhibitor). Expression levels of PLAP-1 and HIF-1α were examined by real-time reverse transcription-polymerase chain reaction and western blot analysis. Luciferase reporter assays of HIF-1α activity were performed using 293T cells stably transfected with a hypoxia response element (HRE)-containing luciferase vector in the presence or absence of recombinant PLAP-1 or PLAP-1 gene transfection.

RESULTS

Cultivation under hypoxic conditions elevated the gene and protein expression levels of PLAP-1 in HPDLs. Deferoxamine mesylate treatment also enhanced PLAP-1 expression in HPDLs. Hypoxia-induced PLAP-1 expression was significantly suppressed in the presence of chetomin. PLAP-1-suppressed HPDLs showed increased HIF-1α accumulation in the nucleus during culture under hypoxic conditions, but not in the presence of recombinant PLAP-1. In the presence of recombinant PLAP-1, hypoxia-induced HRE activity of 293T cells was significantly suppressed in a dose-dependent manner. Transfection of the PLAP-1 gene resulted in a significant reduction of HRE activity during culture under hypoxic conditions.

CONCLUSION

PLAP-1 expression is upregulated under hypoxic conditions through HIF-1α activation. Moreover, hypoxia-induced PLAP-1 expression regulates HIF-1α signaling.

Functional annotation of regulatory elements in cattle genome reveals the roles of extracellular interaction and dynamic change of chromatin states in rumen development during weaning

We profiled landscapes of bovine regulatory elements and explored dynamic changes of chromatin states in rumen development during weaning. The regulatory elements (15 chromatin states) and their coordinated activities in cattle were defined through genome-wide profiling of four histone modifications, CTCF-binding, DNA accessibility, DNA methylation, and transcriptome in rumen epithelial tissues. Each chromatin state presented specific enrichment for sequence ontology, methylation, trait-associated variants, transcription, gene expression-associated variants, selection signatures, and evolutionarily conserved elements. During weaning, weak enhancers and flanking active transcriptional start sites (TSS) were the most dynamic chromatin states and occurred in tandem with significant variations in gene expression and DNA methylation, significantly associated with stature, production, and reproduction economic traits. By comparing with in vitro cultured epithelial cells and in vivo rumen tissues, we showed the commonness and uniqueness of these results, especially the roles of cell interactions and mitochondrial activities in tissue development.

Impairment of the Hif-1α regulatory pathway in Foxn1-deficient (Foxn1-/- ) mice affects the skin wound healing process

Hypoxia and hypoxia-regulated factors (eg, hypoxia-inducible factor-1α [Hif-1α], factor inhibiting Hif-1α [Fih-1], thioredoxin-1 [Trx-1], aryl hydrocarbon receptor nuclear translocator 2 [Arnt-2]) have essential roles in skin wound healing. Using Foxn1^-/- mice that can heal skin injuries in a unique scarless manner, we investigated the interaction between Foxn1 and hypoxia-regulated factors. The Foxn1^-/- mice displayed impairments in the regulation of Hif-1α, Trx-1, and Fih-1 but not Arnt-2 during the healing process. An analysis of wounded skin showed that the skin of the Foxn1^-/- mice healed in a scarless manner, displaying rapid re-epithelialization and an increase in transforming growth factor β (Tgfβ-3) and collagen III expression. An in vitro analysis revealed that Foxn1 overexpression in keratinocytes isolated from the skin of the Foxn1^-/- mice led to reduced Hif-1α expression in normoxic but not hypoxic cultures and inhibited Fih-1 expression exclusively under hypoxic conditions. These data indicate that in the skin, Foxn1 affects hypoxia-regulated factors that control the wound healing process and suggest that under normoxic conditions, Foxn1 is a limiting factor for Hif-1α.

Preconditioning of surgical pedicle flaps with DNA plasmid expressing hypoxia-inducible factor-1α (HIF-1α) promotes tissue viability

Ischemic necrosis of surgical flaps after reconstruction is a major clinical problem. Hypoxia-inducible factor-1α (HIF-1α) is considered the master regulator of the adaptive response to hypoxia. Among its many properties, it regulates the expression of genes encoding angiogenic growth factors, which have a short half-life in vivo. To achieve a continuous application of the therapeutic, we utilized DNA plasmid delivery. Transcription of the DNA plasmid confirmed by qRT-PCR showed significantly increased mRNA for HIF-1α in the transfected tissue compared to saline control tissue. Rats were preconditioned by injecting with either HIF-1α DNA plasmid or saline intradermally in the designated flap region on each flank. Seven days after preconditioning, each rat had two isolated pedicle flaps raised with a sterile silicone sheet implanted between the skin flap and muscle layer. The flaps preconditioned with HIF-1α DNA plasmid had significantly less necrotic area. Angiogenesis measured by CD31 staining showed a significant increase in the number of vessels per high powered field in the HIF-1α group (p < 0.05). Our findings offer a potential therapeutic strategy for significantly promoting the viability of surgical pedicle flaps by ischemic preconditioning with HIF-1α DNA plasmid.

Single-cell transcriptomic analyses of dairy cattle ruminal epithelial cells during weaning

Using the 10× Genomics Chromium Controller, we obtained scRNA-seq data of 5064 and 1372 individual cells from two Holstein calf ruminal epithelial tissues before and after weaning, respectively. We detected six distinct cell clusters, designated their cell types, and reported their marker genes. We then examined these clusters' underlining cell types and relationships by performing cell cycle, pseudotime trajectory, regulatory network, weighted gene co-expression network and gene ontology analyses. By integrating these cell marker genes with Holstein GWAS signals, we found they were enriched for animal production and body conformation traits. Finally, we confirmed their cell identities by comparing them with human and mouse stomach epithelial cells. This study presents an initial effort to implement single-cell transcriptomic analysis in cattle, and demonstrates ruminal tissue epithelial cell types and their developments during weaning, opening the door for new discoveries about tissue/cell type roles in complex traits at single-cell resolution.

Inhibition of HIF-prolyl hydroxylases improves healing of intestinal anastomoses

Anastomotic leakage (AL) accounts for a major part of in-house mortality in patients undergoing colorectal surgery. Local ischemia and abdominal sepsis are common risk factors contributing to AL and are characterized by upregulation of the hypoxia-inducible factor (HIF) pathway. The HIF pathway is critically regulated by HIF-prolyl hydroxylases (PHDs). Here, we investigated the significance of PHDs and the effects of pharmacologic PHD inhibition (PHI) during anastomotic healing. Ischemic or septic colonic anastomoses were created in mice by ligation of mesenteric vessels or lipopolysaccharide-induced abdominal sepsis, respectively. Genetic PHD deficiency (Phd1-/-, Phd2+/-, and Phd3-/-) or PHI were applied to manipulate PHD activity. Pharmacologic PHI and genetic PHD2 haplodeficiency (Phd2+/-) significantly improved healing of ischemic or septic colonic anastomoses, as indicated by increased bursting pressure and reduced AL rates. Only Phd2+/- (but not PHI or Phd1-/-) protected from sepsis-related mortality. Mechanistically, PHI and Phd2+/- induced immunomodulatory (M2) polarization of macrophages, resulting in increased collagen content and attenuated inflammation-driven immune cell recruitment. We conclude that PHI improves healing of colonic anastomoses in ischemic or septic conditions by Phd2+/--mediated M2 polarization of macrophages, conferring a favorable microenvironment for anastomotic healing. Patients with critically perfused colorectal anastomosis or abdominal sepsis could benefit from pharmacologic PHI.

Hypoxia stimulates collagen hydroxylation in gingival fibroblasts and periodontal ligament cells

BACKGROUND

Cellular responses to hypoxia regulate various biological events, including angiogenesis and extracellular matrix metabolism. Collagen is a major component of the extracellular matrix in periodontal tissues and its coordinated production is essential for tissue homeostasis. In this study, we investigated the effects of hypoxia on collagen production in human gingival fibroblasts (HGFs) and human periodontal ligament cells (HPDLs).

METHODS

HGFs and HPDLs were cultured under either normoxic (20% O₂ ) or hypoxic (1% O₂ ) conditions. Nuclear expression of hypoxia-inducible factor-1α (HIF-1α) was determined by western blotting. Peri-cellular expression of type I collagen was examined by immunocytochemistry analysis. Synthesis of type I collagen was evaluated by measuring the concentration of procollagen type I C-peptide (PIP) in culture supernatant using enzyme-linked immunosorbent assay. Expression of collagen hydroxylase enzymes prolyl 4-hydroxylase alpha polypeptide 1 (P4HA1) and 2-oxoglutarate 5-dioxygenase 2 (PLOD2) was determined by RT-qPCR and western blotting. The roles of these enzymes were analyzed using siRNA transfection.

RESULTS

Cultivation under hypoxic conditions stimulated type I collagen production via HIF-1α in both cell types. Interestingly, hypoxic conditions did not affect collagen 1a1 or 1a2 gene expression but upregulated that of P4HA1 and PLOD2. Additionally, suppressing P4HA1 significantly decreased the levels of hypoxia-induced procollagen type I C-peptide, a product of stable triple helical collagen, in the supernatant. In contrast, PLOD2 suppression decreased cross-linked collagen expression in the pericellular region.

CONCLUSION

Our results suggest that hypoxia activates collagen synthesis in HGFs and HPDLs by upregulating hydroxylases P4HA1 and PLOD2 in an HIF-1α-dependent manner.

The Expression and Role of Hypoxia-induced Factor-1α in Human Tenon's Capsule Fibroblasts under Hypoxia

PURPOSE

To determine the expression of hypoxia-induced factor-1α (HIF-1α) and its downstream factors in human Tenon's capsule fibroblasts (HTFs) and changes in HTFs biological functions, we explored the role of HIF-1α in HTFs under hypoxia to provide a basis for studying the regulation of HIF-1α in wound healing after glaucoma surgery.

MATERIALS AND METHODS

we established HTFs hypoxia model in vitro, meanwhile the HIF-1α agonist VH298 or inhibitor KC7F2 was added to HTFs, and the normoxia group was used as a control. Western blot, immunofluorescence and ELISA were used to detect the expression of HIF-1α, vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β), Smads and collagen I. The proliferation of HTFs was quantified by cell counting kit-8, and cell migration was tested by healing scratch test.

RESULTS

HIF-1α protein expression increased under hypoxia, peaked from 4-24 h, and then decreased. The secretion of VEGF and TGF-β increased with prolonged hypoxia time. VH298 and KC7F2 upregulated and downregulated the levels of VEGF and TGF-β, respectively, suggesting that HIF-1α upregulates and downregulates the levels of VEGF and TGF-β in HTFs under hypoxia, respectively. HIF-1α upregulated the proliferation, migration and collagen synthesis of HTFs under hypoxia.

CONCLUSIONS

Regulating HIF-1α and its downstream factors effectively regulated HTFs proliferation, migration and collagen synthesis. HIF-1α is a promising regulator in the study of wound healing after glaucoma surgery.

Understanding Transcriptional Networks Regulating Initiation of Cutaneous Wound Healing

The epidermis has an essential function in creating a barrier against the external environment to retain proper fluid balance and block the entry of pathogens. When damage occurs to this barrier, the wound must quickly be sealed to avoid fluid loss, cleared of invading pathogens, and then keratinocytes must re-form an intact barrier. This requires complex integration of temporally and spatially distinct signals to execute orderly closure of the wound, and failure of this process can lead to chronic ulceration. Transcription factors serve as a key integration point for the myriad of information coming from the external environment, allowing for an orderly process of re-epithelialization. Importantly, transcription factors engage with and alter the chromatin structure around key target genes through association with different chromatin-modifying complexes. In this review, we will discuss the current understanding of how transcription is regulated during the initiation of re-epithelialization, and the exciting technological advances that will allow for a more refined mechanistic understanding of the re-epithelialization process.

Transcriptome Analysis Reveals That Alfalfa Promotes Rumen Development Through Enhanced Metabolic Processes and Calcium Transduction in Hu Lambs

A healthy gut is very important for young animal development. The rumen of ruminants expands in size with the colonization of microbiota by 2 months of age. This process is promoted by alfalfa intervention. To elucidate the mechanism of this promotion, we performed transcriptomic analyses using a cohort of 23 lambs to evaluate the effects of starter diets plus alfalfa on the development of the rumen wall from the pre- to the postweaning period. The quantitative PCR analyses were used to validate selected genes that were differentially expressed in the transcriptome mapping. We found that several metabolic processes associated with rumen tissue development were affected by solid feed intake, with genes linked to the calcium signaling transduction pathway and the metabolism of pteridine-containing compounds and homocysteine metabolic process being upregulated in the group with alfalfa intervention. The results suggest that the pteridine-containing compounds and calcium signaling are targets for precise regulation of rumen development.

Human keratinocyte-derived microvesicle miRNA-21 promotes skin wound healing in diabetic rats through facilitating fibroblast function and angiogenesis

Skin wound healing is a complex physiological process that maintains the integrity of the skin tissues, involving a variety of distinct cell types and signaling molecules. The specific signaling pathways or extracellular cues that govern the healing processes remain elusive. Microvesicles (MVs) have recently emerged as critical mediators of cell communication by delivery of genetic materials to target cells. In this study, we found the direct delivery of HEKa-MVs expressing miR-21 mimics significantly promoted the healing of skin wound in diabetic rats. In-depth studies showed that MV miR-21 promoted fibroblast migration, differentiation, and contraction, induced a pro-angiogenic process of endothelial cells and mediated a pro-inflammatory response. Mechanically, MV miR-21 might target specific essential effector mRNA in fibroblasts such as MMP-1, MMP-3, TIMP3, and TIMP4 to increase MMPs expression and enzymatic activities. Moreover, MV miR-21 regulated ɑ-SMA and N-cadherin to induce fibroblast-myofibroblast differentiation. MV miR-21 up-regulated the IL-6 and IL-8 expressions and their secretion to amplify the immune response. Furthermore, MV miR-21 down-regulated PTEN and RECK in protein level, and activate MAPK/ERK signaling cascade, thereby promoting fibroblast functions. Thus, our study has provided for the first time the basis for the potential application of HEKa-MVs, and MV miR-21 in particular for wound healing.

PHD-2 Suppression in Mesenchymal Stromal Cells Enhances Wound Healing

BACKGROUND

Cell therapy with mesenchymal stromal cells is a promising strategy for tissue repair. Restoration of blood flow to ischemic tissues is a key step in wound repair, and mesenchymal stromal cells have been shown to be proangiogenic. Angiogenesis is critically regulated by the hypoxia-inducible factor (HIF) superfamily, consisting of transcription factors targeted for degradation by prolyl hydroxylase domain (PHD)-2. The aim of this study was to enhance the proangiogenic capability of mesenchymal stromal cells and to use these modified cells to promote wound healing.

METHODS

Mesenchymal stromal cells harvested from mouse bone marrow were transduced with short hairpin RNA (shRNA) against PHD-2; control cells were transduced with scrambled shRNA (shScramble) construct. Gene expression quantification, human umbilical vein endothelial cell tube formation assays, and wound healing assays were used to assess the effect of PHD knockdown mesenchymal stromal cells on wound healing dynamics.

RESULTS

PHD-2 knockdown mesenchymal stromal cells overexpressed HIF-1α and multiple angiogenic factors compared to control (p < 0.05). Human umbilical vein endothelial cells treated with conditioned medium from PHD-2 knockdown mesenchymal stromal cells exhibited increased formation of capillary-like structures and enhanced migration compared with human umbilical vein endothelial cells treated with conditioned medium from shScramble-transduced mesenchymal stromal cells (p < 0.05). Wounds treated with PHD-2 knockdown mesenchymal stromal cells healed at a significantly accelerated rate compared with wounds treated with shScramble mesenchymal stromal cells (p < 0.05). Histologic studies revealed increased blood vessel density and increased cellularity in the wounds treated with PHD-2 knockdown mesenchymal stromal cells (p < 0.05).

CONCLUSIONS

Silencing PHD-2 in mesenchymal stromal cells augments their proangiogenic potential in wound healing therapy. This effect appears to be mediated by overexpression of HIF family transcription factors and up-regulation of multiple downstream angiogenic factors.

Pharmacological HIF-inhibition attenuates postoperative adhesion formation

Peritoneal adhesions represent a common complication of abdominal surgery, and tissue hypoxia is a main determinant in adhesion formation. Reliable therapeutic options to reduce peritoneal adhesions are scarce. We investigated whether the formation of postsurgical adhesions can be affected by pharmacological interference with hypoxia-inducible factors (HIFs). Mice were treated with a small molecule HIF-inhibitor, YC-1 (3-[5′-Hydroxymethyl-2′-furyl]-1-benzyl-indazole), or vehicle three days before and seven days after induction of peritoneal adhesions or, alternatively, once during induction of peritoneal adhesions. Pretreatment or single intraperitoneal lavage with YC-1 significantly reduced postoperative adhesion formation without prompting systemic adverse effects. Expression analyses of cytokines in peritoneal tissue and fluid and in vitro assays applying macrophages and peritoneal fibroblasts indicated that this effect was cooperatively mediated by various putatively HIF-1α-dependent mechanisms, comprising attenuated pro-inflammatory activation of macrophages, impaired recruitment and activation of peritoneal fibroblasts, mitigated epithelial-mesenchymal-transition (EMT), as well as enhanced fibrinolysis and impaired angiogenesis. Thus, this study identifies prevention of postsurgical peritoneal adhesions as a novel and promising field for the application of HIF inhibitors in clinical practice.

Intestinal hypoxia and hypoxia-induced signalling as therapeutic targets for IBD

Tissue hypoxia occurs when local oxygen demand exceeds oxygen supply. In chronic inflammatory conditions such as IBD, the increased oxygen demand by resident and gut-infiltrating immune cells coupled with vascular dysfunction brings about a marked reduction in mucosal oxygen concentrations. To counter the hypoxic challenge and ensure their survival, mucosal cells induce adaptive responses, including the activation of hypoxia-inducible factors (HIFs) and modulation of nuclear factor-κB (NF-κB). Both pathways are tightly regulated by oxygen-sensitive prolyl hydroxylases (PHDs), which therefore represent promising therapeutic targets for IBD. In this Review, we discuss the involvement of mucosal hypoxia and hypoxia-induced signalling in the pathogenesis of IBD and elaborate in detail on the role of HIFs, NF-κB and PHDs in different cell types during intestinal inflammation. We also provide an update on the development of PHD inhibitors and discuss their therapeutic potential in IBD.

Hypoxia Inducible Factor (HIF) Hydroxylases as Regulators of Intestinal Epithelial Barrier Function

Human health is dependent on the ability of the body to extract nutrients, fluids, and oxygen from the external environment while at the same time maintaining a state of internal sterility. Therefore, the cell layers that cover the surface areas of the body such as the lung, skin, and gastrointestinal mucosa provide vital semipermeable barriers that allow the transport of essential nutrients, fluid, and waste products, while at the same time keeping the internal compartments free of microbial organisms. These epithelial surfaces are highly specialized and differ in their anatomic structure depending on their location to provide appropriate and effective site-specific barrier function. Given this important role, it is not surprising that significant disease often is associated with alterations in epithelial barrier function. Examples of such diseases include inflammatory bowel disease, chronic obstructive pulmonary disease, and atopic dermatitis. These chronic inflammatory disorders often are characterized by diminished tissue oxygen levels (hypoxia). Hypoxia triggers an adaptive transcriptional response governed by hypoxia-inducible factors (HIFs), which are repressed by a family of oxygen-sensing HIF hydroxylases. Here, we review recent evidence suggesting that pharmacologic hydroxylase inhibition may be of therapeutic benefit in inflammatory bowel disease through the promotion of intestinal epithelial barrier function through both HIF-dependent and HIF-independent mechanisms.

Notch1 Signaling Contributes to Hypoxia-induced High Expression of Integrin β1 in Keratinocyte Migration

Oxygen tension is an important micro-environmental factor that affects epidermal development and function. After injury, high oxygen consumption and vascular injury result in partial hypoxia. However, whether hypoxia benefits or hurts wound healing remains controversial. In this study, a tissue oxygen tension monitor was used to detect the spatial and temporal distribution of oxygen in burn wounds. In vitro, we demonstrate that hypoxia promoted the expression of integrin β1 and the migration of keratinocytes. Furthermore, hypoxia-induced migration was slowed by Notch1 ligands and a siRNA against ITGB1 (integrin β1). Our findings suggest that integrin β1 may be an oxygen-sensitive molecule that promotes keratinocyte migration during wound healing and that Notch1 signaling is involved in this process.

Hydroxylase inhibition regulates inflammation-induced intestinal fibrosis through the suppression of ERK-mediated TGF-β1 signaling. [corrected]

Fibrosis is a complication of chronic inflammatory disorders such as inflammatory bowel disease, a condition which has limited therapeutic options and often requires surgical intervention. Pharmacologic inhibition of oxygen-sensing prolyl hydroxylases, which confer oxygen sensitivity upon the hypoxia-inducible factor pathway, has recently been shown to have therapeutic potential in colitis, although the mechanisms involved remain unclear. Here, we investigated the impact of hydroxylase inhibition on inflammation-driven fibrosis in a murine colitis model. Mice exposed to dextran sodium sulfate, followed by a period of recovery, developed intestinal fibrosis characterized by alterations in the pattern of collagen deposition and infiltration of activated fibroblasts. Treatment with the hydroxylase inhibitor dimethyloxalylglycine ameliorated fibrosis. TGF-β1 is a key regulator of fibrosis that acts through the activation of fibroblasts. Hydroxylase inhibition reduced TGF-β1-induced expression of fibrotic markers in cultured fibroblasts, suggesting a direct role for hydroxylases in TGF-β1 signaling. This was at least in part due to inhibition of noncanonical activation of extracellular signal-regulated kinase (ERK) signaling. In summary, pharmacologic hydroxylase inhibition ameliorates intestinal fibrosis through suppression of TGF-β1-dependent ERK activation in fibroblasts. We hypothesize that in addition to previously reported immunosupressive effects, hydroxylase inhibitors independently suppress profibrotic pathways.

Local Delivery of PHD2 siRNA from ROS-Degradable Scaffolds to Promote Diabetic Wound Healing

Small interfering RNA (siRNA) delivered from reactive oxygen species-degradable tissue engineering scaffolds promotes diabetic wound healing in rats. Porous poly(thioketal-urethane) scaffolds implanted in diabetic wounds locally deliver siRNA that inhibits the expression of prolyl hydroxylase domain protein 2, thereby increasing the expression of progrowth genes and increasing vasculature, proliferating cells, and tissue development in diabetic wounds.

New Insights into Protein Hydroxylation and Its Important Role in Human Diseases

Protein hydroxylation is a post-translational modification catalyzed by 2-oxoglutarate-dependent dioxygenases. The hydroxylation modification can take place on various amino acids, including but not limited to proline, lysine, asparagine, aspartate and histidine. A classical example of this modification is hypoxia inducible factor alpha (HIF-α) prolyl hydroxylation, which affects HIF-α protein stability via the Von-Hippel Lindau (VHL) tumor suppressor pathway, a Cullin 2-based E3 ligase adaptor protein frequently mutated in kidney cancer. In addition to protein stability regulation, protein hydroxylation may influence other post-translational modifications or the kinase activity of the modified protein (such as Akt and DYRK1A/B). In other cases, protein hydroxylation may alter protein-protein interaction and its downstream signaling events in vivo (such as OTUB1, MAPK6 and eEF2K). In this review, we highlight the recently identified protein hydroxylation targets and their pathophysiological roles, especially in cancer settings. Better understanding of protein hydroxylation will help identify novel therapeutic targets and their regulation mechanisms to foster development of more effective treatment strategies for various human cancers.

Hypoxia-dependent regulation of inflammatory pathways in immune cells

Uncontrolled inflammation underpins a diverse range of diseases where effective therapy remains an unmet clinical need. Hypoxia is a prominent feature of the inflammatory microenvironment that regulates key transcription factors including HIF and NF-κB in both innate and adaptive immune cells. In turn, altered activity of the pathways controlled by these factors can affect the course of inflammation through the regulation of immune cell development and function. In this review, we will discuss these pathways and the oxygen sensors that confer hypoxic sensitivity in immune cells. Furthermore, we will describe how hypoxia-dependent pathways contribute to immunity and discuss their potential as therapeutic targets in inflammatory and infectious disease.

PHD2: from hypoxia regulation to disease progression

Oxygen represents one of the major molecules required for the development and maintenance of life. An adequate response to hypoxia is therefore required for the functioning of the majority of living organisms and relies on the activation of the hypoxia-inducible factor (HIF) pathway. HIF prolyl hydroxylase domain-2 (PHD2) has long been recognized as the major regulator of this response, controlling a myriad of outcomes that range from cell death to proliferation. However, this enzyme has been associated with more pathways, making the role of this protein remarkably complex under distinct pathologies. While a protective role seems to exist in physiological conditions such as erythropoiesis; the picture is more complex during pathologies such as cancer. Since the regulation of this enzyme and its closest family members is currently considered as a possible therapy for various diseases, understanding the different particular roles of this protein is essential.

Pharmacological targeting of the HIF hydroxylases--A new field in medicine development

In human cells oxygen levels are 'sensed' by a set of ferrous iron and 2-oxoglutarate dependent dioxygenases. These enzymes regulate a broad range of cellular and systemic responses to hypoxia by catalysing the post-translational hydroxylation of specific residues in the alpha subunits of hypoxia inducible factor (HIF) transcriptional complexes. The HIF hydroxylases are now the subject of pharmaceutical targeting by small molecule inhibitors that aim to activate or augment the endogenous HIF transcriptional response for the treatment of anaemia and other hypoxic human diseases. Here we consider the rationale for this therapeutic strategy from the biochemical, biological and medical perspectives. We outline structural and mechanistic considerations that are relevant to the design of HIF hydroxylase inhibitors, including likely determinants of specificity, and review published reports on their activity in pre-clinical models and clinical trials.

The role of HIF in immunity and inflammation

Uncontrolled or non-resolving inflammation underpins a range of disease states including rheumatoid arthritis, inflammatory bowel disease and atherosclerosis. Hypoxia is a prominent feature of chronically inflamed tissues. This is due to elevated oxygen consumption by highly metabolically active inflamed resident cells and activated infiltrating immunocytes, as well as diminished oxygen supply due to vascular dysfunction. Tissue hypoxia can have a significant impact upon inflammatory signaling pathways in immune and non-immune cells and this can impact upon disease progression. In this review, we will discuss the relationship between tissue hypoxia and inflammation and identify how hypoxia-sensitive signaling pathways are potential therapeutic targets in chronic inflammatory disease.

Recent Advances in Developing Inhibitors for Hypoxia-Inducible Factor Prolyl Hydroxylases and Their Therapeutic Implications

Hypoxia-inducible factor (HIF) prolyl hydroxylases (PHDs) are members of the 2-oxoglutarate dependent non-heme iron dioxygenases. Due to their physiological roles in regulation of HIF-1α stability, many efforts have been focused on searching for selective PHD inhibitors to control HIF-1α levels for therapeutic applications. In this review, we first describe the structure of PHD2 as a molecular basis for structure-based drug design (SBDD) and various experimental methods developed for measuring PHD activity. We further discuss the current status of the development of PHD inhibitors enabled by combining SBDD approaches with high-throughput screening. Finally, we highlight the clinical implications of small molecule PHD inhibitors.

The role of placenta-derived mesenchymal stem cells in healing of induced full-thickness skin wound in a mouse model

We examined the effect of placenta-derived MSCs (PDMSCs) injection intraregionally and intraperitoneally on healing of induced full thickness mice skin wounds; moreover, the mechanisms by which MSCs exert their effects were also studied. Sixty female mice were divided into three groups after induction of full thickness skin wound; untreated group, wounded mice were injected with MSCs derived from human placenta intraperitoneally or intraregionally. Skin biopsies were obtained 7 and 12 days after wound incision for histological examinations, detection of vascular endothelial growth factor (VEGF) by ELISA, and estimation of expression of mouse ICAM-1, Integrin β1, Integrin β3 genes and human albumin and GAPDH genes by reverse transcription polymerase chain reaction. Human placenta derived-MSCs treated groups showed accelerated wound healing than non-treated group. VEGF, Integrin β1, and Integrin β3 levels were significantly increased in the intraregionally and intraperitoneally treated mice as compared to non-treated group at day 7 after wound induction. ICAM-1 showed significant decrease in its expression in treated groups compared with non-treated group. Interestingly, the intraperitoneal MSCs injections showed better results than intraregional one. PDMSCs accelerate full thickness skin wound healing and the intraperitoneal MSCs injections are more effective than intraregional one. MSCs promote wound healing through release of proangiogenic factors as VEGF, increase healing promoting factors as integrin β1 and β3, and decrease proinflammatory cytokines as ICAM-1.

A distinct regulatory region of the Bmp5 locus activates gene expression following adult bone fracture or soft tissue injury

Bone morphogenetic proteins (BMPs) are key signaling molecules required for normal development of bones and other tissues. Previous studies have shown that null mutations in the mouse Bmp5 gene alter the size, shape and number of multiple bone and cartilage structures during development. Bmp5 mutations also delay healing of rib fractures in adult mutants, suggesting that the same signals used to pattern embryonic bone and cartilage are also reused during skeletal regeneration and repair. Despite intense interest in BMPs as agents for stimulating bone formation in clinical applications, little is known about the regulatory elements that control developmental or injury-induced BMP expression. To compare the DNA sequences that activate gene expression during embryonic bone formation and following acute injuries in adult animals, we assayed regions surrounding the Bmp5 gene for their ability to stimulate lacZ reporter gene expression in transgenic mice. Multiple genomic fragments, distributed across the Bmp5 locus, collectively coordinate expression in discrete anatomic domains during normal development, including in embryonic ribs. In contrast, a distinct regulatory region activated expression following rib fracture in adult animals. The same injury control region triggered gene expression in mesenchymal cells following tibia fracture, in migrating keratinocytes following dorsal skin wounding, and in regenerating epithelial cells following lung injury. The Bmp5 gene thus contains an "injury response" control region that is distinct from embryonic enhancers, and that is activated by multiple types of injury in adult animals.

Impairment of hypoxia-induced HIF-1α signaling in keratinocytes and fibroblasts by sulfur mustard is counteracted by a selective PHD-2 inhibitor

Skin exposure to sulfur mustard (SM) provokes long-term complications in wound healing. Similar to chronic wounds, SM-induced skin lesions are associated with low levels of oxygen in the wound tissue. Normally, skin cells respond to hypoxia by stabilization of the transcription factor hypoxia-inducible factor 1 alpha (HIF-1α). HIF-1α modulates expression of genes including VEGFA, BNIP3, and MMP2 that control processes such as angiogenesis, growth, and extracellular proteolysis essential for proper wound healing. The results of our studies revealed that exposure of primary normal human epidermal keratinocytes (NHEK) and primary normal human dermal fibroblasts (NHDF) to SM significantly impaired hypoxia-induced HIF-1α stabilization and target gene expression in these cells. Addition of a selective inhibitor of the oxygen-sensitive prolyl hydroxylase domain-containing protein 2 (PHD-2), IOX2, fully recovered HIF-1α stability, nuclear translocation, and target gene expression in NHEK and NHDF. Moreover, functional studies using a scratch wound assay demonstrated that the application of IOX2 efficiently counteracted SM-mediated deficiencies in monolayer regeneration under hypoxic conditions in NHEK and NHDF. Our findings describe a pathomechanism by which SM negatively affects hypoxia-stimulated HIF-1α signaling in keratinocytes and fibroblasts and thus possibly contributes to delayed wound healing in SM-injured patients that could be treated with PHD-2 inhibitors.

Epidermal closure regulates histolysis during mammalian (Mus) digit regeneration

Mammalian digit regeneration progresses through consistent stages: histolysis, inflammation, epidermal closure, blastema formation, and finally redifferentiation. What we do not yet know is how each stage can affect others. Questions of stage timing, tissue interactions, and microenvironmental states are becoming increasingly important as we look toward solutions for whole limb regeneration. This study focuses on the timing of epidermal closure which, in mammals, is delayed compared to more regenerative animals like the axolotl. We use a standard wound closure device, Dermabond (2-octyl cyanoacrylate), to induce earlier epidermal closure, and we evaluate the effect of fast epidermal closure on histolysis, blastema formation, and redifferentiation. We find that fast epidermal closure is reliant upon a hypoxic microenvironment. Additionally, early epidermal closure eliminates the histolysis stage and results in a regenerate that more closely replicates the amputated structure. We show that tools like Dermabond and oxygen are able to independently influence the various stages of regeneration enabling us to uncouple histolysis, wound closure, and other regenerative events. With this study, we start to understand how each stage of mammalian digit regeneration is controlled.

Formalin evokes calcium transients from the endoplasmatic reticulum

The formalin test is the most widely used behavioral screening test for analgesic compounds. The cellular mechanism of action of formaldehyde, inducing a typically biphasic pain-related behavior in rodents is addressed in this study. The chemoreceptor channel TRPA1 was suggested as primary transducer, but the high concentrations used in the formalin test elicit a similar response in TRPA1 wildtype and knockout animals. Here we show that formaldehyde evokes a dose-dependent calcium release from intracellular stores in mouse sensory neurons and primary keratinocytes as well as in non-neuronal cell lines, and independent of TRPA1. The source of calcium is the endoplasmatic reticulum and inhibition of the sarco/endoplasmic reticulum calcium-ATPase has a major contribution. This TRPA1-independent mechanism may underlie formaldehyde-induced pan-neuronal excitation and subsequent inflammation.

Therapeutic inhibition of prolyl hydroxylase domain-containing enzymes in surgery: putative applications and challenges

Oxygen is essential for metazoans to generate energy. Upon oxygen deprivation adaptive and protective pathways are induced, mediated by hypoxia-inducible factors (HIFs) and prolyl hydroxylase domain-containing enzymes (PHDs). Both play a pivotal role in various conditions associated with prolonged ischemia and inflammation, and are promising targets for therapeutic intervention. This review focuses on aspects of therapeutic PHD modulation in surgically relevant disease conditions such as hepatic and intestinal disorders, wound healing, innate immune responses, and tumorigenesis, and discusses the therapeutic potential and challenges of PHD inhibition in surgical patients.

Signaling hypoxia by hypoxia-inducible factor protein hydroxylases: a historical overview and future perspectives

By the early 1900s, the close matching of oxygen supply with demand was recognized to be a fundamental requirement for physiological function, and multiple adaptive responses to environment hypoxia had been described. Nevertheless, the widespread operation of mechanisms that directly sense and respond to levels of oxygen in animal cells was not appreciated for most of the twentieth century with investigators generally stressing the regulatory importance of metabolic products. Work over the last 25 years has overturned that paradigm. It has revealed the existence of a set of “oxygen-sensing” 2-oxoglutarate dependent dioxygenases that catalyze the hydroxylation of specific amino acid residues and thereby control the stability and activity of hypoxia-inducible factor. The hypoxia-inducible factor hydroxylase pathway regulates a massive transcriptional cascade that is operative in essentially all animal cells. It transduces a wide range of responses to hypoxia, extending well beyond the classical boundaries of hypoxia physiology. Here we review the discovery and elucidation of these pathways, and consider the opportunities and challenges that have been brought into focus by the findings, including new implications for the integrated physiology of hypoxia and therapeutic approaches to ischemic/hypoxic disease.

Regulation of wound healing and fibrosis by hypoxia and hypoxia-inducible factor-1

Wound healing is a complex multi-step process that requires spatial and temporal orchestration of cellular and non-cellular components. Hypoxia is one of the prominent microenvironmental factors in tissue injury and wound healing. Hypoxic responses, mainly mediated by a master transcription factor of oxygen homeostasis, hypoxia-inducible factor-1 (HIF-1), have been shown to be critically involved in virtually all processes of wound healing and remodeling. Yet, mechanisms underlying hypoxic regulation of wound healing are still poorly understood. Better understanding of how the wound healing process is regulated by the hypoxic microenvironment and HIF-1 signaling pathway will provide insight into the development of a novel therapeutic strategy for impaired wound healing conditions such as diabetic wound and fibrosis. In this review, we will discuss recent studies illuminating the roles of HIF-1 in physiologic and pathologic wound repair and further, the therapeutic potentials of HIF-1 stabilization or inhibition.

[What's new in dermatological research?]

In 2013, news from research has clearly shown that dermatology is bound to occupy a more important place in fundamental research. Among these evidences are an increasing number of papers devoted to "Skin" in journals with the highest impact factors and the excellence of the scientific program of the International Investigative Dermatology Meeting held in May in Edinburgh. This paper outlines a selection of scientific works published between September 2012 and August 2013 or presented as communications at the IID Meeting. This selection was made based on the quality of methods used by the authors to obtain results, and on the impact of these scientific results in terms of pathophysiological and therapeutical advances.

Wound healing improvement with PHD-2 silenced fibroblasts in diabetic mice

BACKGROUND

Hypoxia-inducible factor 1α is the central regulator of the hypoxia-induced response which results in the up-regulation of angiogenic factors. Its activity is under precise regulation of prolyl-hydroxylase domain 2. We hypothesized that PHD2 silenced fibroblasts would increase the expression of angiogenic factors, which might contribute to the improvement of the diabetic wound healing.

MATERIALS AND METHODS

50 dB/db mice were employed and randomly assigned into five groups with 10 mice in each: group 1 (untreated cell), group 2 (PHD2 silenced cell), group 3 (L-mimosine treated cells), group 4 (nontargeting siRNA treated cells) and group 5 (sham control). Fibroblasts were cultivated from the dermis of mice in each group and treated with PHD2 targeting siRNA, L-mimosine and non-targeting siRNA respectively. A fraction of the fibroblasts were employed to verify the silencing rate of PHD2 after 48 hours. The autologous fibroblasts (treated and untreated) labeled with adenovirus-GFP were implanted around the wound (Φ6mm), which was created on the dorsum of each mouse. The status of wounds was recorded periodically. Ten days postoperatively, 3 mice from each group were sacrificed and wound tissues were harvested. Molecular biological examinations were performed to evaluate the expressions of cytokines. 28 days postoperatively, the remaining mice were sacrificed. Histological examinations were performed to evaluate the densities of GFP+ cells and capillaries.

RESULTS

The expression of PHD2 reduced to 12.5%, and the expressions of HIF-1α and VEGFa increased significantly after PHD2 siRNA treatment. With the increasing expressions of HIF-1α and VEGFa, the time to wound closure in group 2 was less than 2 weeks. Increased numbers of GFP+ cells and capillaries were observed in group 2.

CONCLUSION

PHD2 siRNA treatment not only increased the expression of HIF1α and VEGFa, but also improved the fibroblast proliferation. These effects might contribute to the improvement of the diabetic wound healing.