Timothy D. Blalock

Interference with Transforming Growth Factor-β/ Smad3 Signaling Results in Accelerated Healing of Wounds in Previously Irradiated Skin

Transforming growth factor (TGF)-beta regulates many aspects of wound repair including inflammation, chemotaxis, and deposition of extracellular matrix. We previously showed that epithelialization of incisional wounds is accelerated in mice null for Smad3, a key cytoplasmic mediator of TGF-beta signaling. Here, we investigated the effects of loss of Smad3 on healing of wounds in skin previously exposed to ionizing radiation, in which scarring fibrosis complicates healing. Cutaneous wounds made in Smad3-null mice 6 weeks after irradiation showed decreased wound widths, enhanced epithelialization, and reduced numbers of neutrophils and myofibroblasts compared to wounds in irradiated wild-type littermates. Differences in breaking strength of wild-type and Smad3-null wounds were not significant. As shown previously for neutrophils, chemotaxis of primary dermal fibroblasts to TGF-beta required Smad3, but differentiation of fibroblasts to myofibroblasts by TGF-beta was independent of Smad3. Previous irradiation-enhanced induction of connective tissue growth factor mRNA in wild-type, but not Smad3-null fibroblasts, suggested that this may contribute to the heightened scarring in irradiated wild-type skin as demonstrated by Picrosirius red staining. Overall, the data suggest that attenuation of Smad3 signaling might improve the healing of wounds in previously irradiated skin commensurate with an inhibition of fibrosis.

Mediation of Transforming Growth Factor-β1-Stimulated Matrix Contraction by Fibroblasts: A Role for Connective Tissue Growth Factor in Contractile Scarring

Excessive cell-mediated tissue contraction after injury can lead to morbid contractile scarring in the body. In the eye this can cause blindness because of posterior capsule opacification, proliferative vitroretinopathy, failure of glaucoma filtration surgery, and corneal haze. During repair, transforming growth factor (TGF)-beta and connective tissue growth factor (CTGF) genes are co-ordinately expressed. Although TGF-beta and CTGF stimulate new matrix deposition, their role and regulation during contractile scarring is unknown. In this study, an in vitro model of collagen matrix contraction culminating from tractional forces generated by fibroblasts showed that both TGF-beta(1) and CTGF-stimulated contraction. Using a specific anti-sense oligodeoxynucleotide to CTGF the procontractile activity of TGF-beta(1) was found to be mediated by CTGF. During contraction fibroblasts produced similar levels of matrix metalloproteinases (MMPs)-2 and -9 with TGF-beta(1) or CTGF and a modest increase in MMP-1 with CTGF only (indicated by zymography and enzyme-linked immunosorbent assay). The requirement of MMPs for contraction was demonstrated using a broad-spectrum synthetic inhibitor. This study demonstrates a new function for CTGF in mediating matrix contraction by fibroblasts involving MMPs and suggests a novel regulatory mechanism for TGF-beta-stimulated contraction. Inhibition of CTGF activity or gene transcription could be a suitable target for anti-scarring therapies.

MUC16 is lost from the uterodome (pinopode) surface of the receptive human endometrium: in vitro evidence that MUC16 is a barrier to trophoblast adherence.

Abstract In order for the preimplantation embryo to implant into the uterus, the trophoblast cells must initially adhere to the uterine epithelial surface. In preparation, the luminal secretory cells of the epithelium lose their nonadhesive character and their surface microvilli and bulge into the lumen, forming uterodomes (pinopodes; uterodome is used instead of pinopode, since in humans the surface membrane exocytoses rather than endocytoses (Murphy, Hum Reprod 2000; 15:2451–2454). Previous research has led to the hypothesis that loss of the nonadhesive membrane-spanning mucin MUC1 from the uterodome surface allows trophoblast adherence. Immunofluorescence microscopic assay of luminal epithelia on human uterine biopsies taken from LH+0 to LH+13 show that another membrane-spanning mucin, MUC16, was lost from uterodome surfaces in all samples taken during the receptive phase, LH+6 to LH+8 (n = 12), and that MUC1 was present on uterodomes in 4 of 12 samples and on all ciliated cells of the epithelium in the receptive phase. Short interfering RNA (siRNA) knockdown of MUC16 in a uterine epithelial cell line ECC-1 that, like uterine epithelium, expresses MUC16 and MUC1 allowed increased adherence of cells of a trophoblast cell line. In parallel experiments, siRNA knockdown of MUC1 did not affect trophoblast cell adherence. These data indicate that MUC16 is a membrane component of the nonreceptive luminal uterine surface, which prevents cell adhesion, and that its removal during uterodome formation facilitates adhesion of the trophoblast.

Release of Membrane-associated Mucins from Ocular Surface Epithelia

PURPOSE Three membrane-associated mucins (MAMs)--MUC1, MUC4, and MUC16--are expressed at the ocular surface epithelium. Soluble forms of MAMs are detected in human tears, but the mechanisms of their release from the apical cells are unknown. The purpose of this study was to identify physiologic agents that induce ocular surface MAM release. METHODS An immortalized human corneal-limbal epithelial cell line (HCLE) expressing the same MAMs as native tissue was used. An antibody specific to the MUC16 cytoplasmic tail was developed to confirm that only the extracellular domain is released into the tear fluid or culture media. Effects of agents that have been shown to be present in tears or are implicated in the release or shedding of MAMs in other epithelia (neutrophil elastase, tumor necrosis factor [TNF]), TNF-alpha-converting enzyme, and matrix metalloproteinase-7 and -9) were assessed on HCLE cells. HCLE cell surface proteins were biotinylated to measure the efficiency of induced MAM release and surface restoration. Effects of induced release on surface barrier function were measured by rose bengal dye penetrance. RESULTS MUC16 in tears and in HCLE-conditioned medium lacked the cytoplasmic tail. TNF induced the release of MUC1, MUC4, and MUC16 from the HCLE surface. Matrix metalloproteinase-7 and neutrophil elastase induced the release of MUC16 but not of MUC1 or MUC4. Neutrophil elastase removed 68% of MUC16, 78% of which was restored to the HCLE cell surface 24 hours after release. Neutrophil elastase-treated HCLE cells showed significantly reduced rose bengal dye exclusion. CONCLUSIONS Results suggest that the extracellular domains of MUC1, MUC4, and MUC16 can be released from the ocular surface by agents in tears. Neutrophil elastase and TNF, present in higher amounts in the tears of patients with dry eye, may cause MAM release, allowing rose bengal staining.

Connective tissue growth factor in pterygium: simultaneous presence with vascular endothelial growth factor - possible contributing factor to conjunctival scarring.

Abstract Background. Various growth factors have been detected in pterygium and been associated with its vasculogenesis. The basic pathophysiological mechanisms responsible especially for the fibrotic activity in pterygium are, however, not yet known. Connective tissue growth factor (CTGF) has been shown to be substantially involved in various processes of fibrosis. We report on the presence of CTGF in pterygium and its simultaneous presence with vascular endothelial growth factor (VEGF). Methods. Samples of pterygium were collected during surgery with informed consent of the patients. Specific, non-commercial primary antibodies against CTGF were used to detect CTGF using immunohistochemistry. Specificity of antibodies was confirmed with Western-blot analysis. The same specimens were stained with commercial antibodies for VEGF. Additionally RT-PCR analysis was performed from pterygium samples. Results. CTGF was detected in the epithelium of all samples as well as in some stromal keratocytes. The RT-PCR confirmed the identity of CTGF in these samples. The staining pattern differed slightly from that of VEGF, which was detected in all samples. The control sections were negative. Conclusion. CTGF is present in the epithelium of a majority of pterygia and probably contributes to fibrosis. Simultaneous presence with VEGF suggests growth factor interaction and possible involvement in apoptotic dysregulation.

Immunohistochemical localization of EGF, TGF-alpha, TGF-beta, and their receptors in rat corneas during healing of excimer laser ablation.

Purpose: Members of the epidermal growth factor (EGF) and transforming growth factor beta (TGF-β) families of growth factors and receptors are known to regulate key aspects of corneal wound healing, including epithelial migration and scar formation. To further understand their roles, mRNA levels were measured and proteins were immunolocalized in rat corneas at multiple time points during healing of excimer laser ablation injury. Methods: Excimer laser photoablation was performed to a depth of 50 μm on rat corneas. Levels of mRNAs for EGF, TGF-α, TGF-β isoforms 1, 2, and 3, and their receptors (EGF-R and TGFβ-IIR) were measured by quantitative RT-PCR on days 0, 1.5, 7, 21, 42, and 91 after ablation. Immunohistochemical localization of the growth factors and their receptors was performed on days 0, 7, and 21 in corneal sections. Results: Levels of EGF mRNA remained stable in rat corneas after ablation (68 ± 12 copies/cell, mean ± SD), whereas levels of TGF-α mRNA progressively increased sixfold to a maximum at day 42 (300 copies/cell) then slightly decreased on day 91. Levels of EGF-R mRNA rapidly increased 60-fold on day 7 compared with day 0 (571 vs. 9 copies/cell) then decreased sixfold above baseline at day 91. Levels of TGF-β1 mRNA remained stable (36 ± 10 copies/cell), whereas levels of TGF-β2 and TGF-β3 mRNAs peaked on day 21 (300-fold and 25-fold increase) and remained elevated through day 91. Levels of TGFβ-IIR mRNA showed a similar pattern. Immunostaining of all the growth factors and receptors was primarily in basal layers of epithelial cells in uninjured cornea and during healing. Intensity of immunostaining for TGF-β1, TGFβ-IR, and TGFβ-IIR increased appreciably in the basal epithelial layers after ablation. Conclusions: Levels of mRNAs for several key members of the EGF and TGF-β systems increase during corneal wound healing. In addition, the proteins are primarily localized in basal layers of epithelial cells, which suggest these cells are active in synthesizing autocrine and paracrine growth factors that modulate corneal wound healing.

Detection of connective tissue growth factor in human aqueous humor.

Purpose: Connective tissue growth factor (CTGF) has been shown to be substantially involved in various processes of fibrosis. We investigated if CTGF is present in aqueous humor (AH). Methods: Samples from AH were collected from 10 volunteers during cataract surgery. Specific ELISA analysis was performed with goat IGG against human CTGF. Results: CTGF was above the detection limit of the assay in 80% of the samples. The concentration of CTGF in the anterior chamber fluid was 1.24 ± (SD) 0.26 ng/ml. Conclusion: CTGF is present in a majority of AH samples, possibly representing a constant component in this fluid. The origin and physiological importance of CTGF is yet unclear. The involvement of CTGF in processes of intraocular fibrosis and wound healing is possible.

Effect of Connective Tissue Growth Factor on Protein Kinase Expression and Activity in Human Corneal Fibroblasts

PURPOSE To investigate signal transduction pathways for connective tissue growth factor (CTGF) in human corneal fibroblasts (HCF). METHODS Expression of 75 kinases in cultures of serum-starved (HCF) were investigated using protein kinase screens, and changes in levels of phosphorylation of 31 different phosphoproteins were determined at 0, 5, and 15 minutes after treatment with CTGF. Levels of phosphorylation of three signal transducing phosphoproteins (extracellular regulated kinase 1 [ERK1], extracellular regulated kinase 2 [ERK2] [MAPKs], and signal transducer and activator of transcription 3 [STAT3]) were measured at nine time points after exposure to CTGF using Western immunoblots. Inhibition of Ras, MEK1/2 (MAPKK), and ERK1/2, on CTGF-stimulated fibroblast proliferation and collagen gel contraction was assessed using selective inhibitors farnesylthiosalicylic acid, PD-98059, and SB203580, respectively. RESULTS Thirty two of the 75 kinases (43%) evaluated by the kinase screen were detected in extracts of quiescent HCF, suggesting these kinases are available to respond acutely to CTGF exposure. Addition of CTGF increased levels of phosphorylation of five phosphoproteins (ERK1 and 2, MEK1/2 [MAPKK], STAT3, and SAPK/JNK), and decreased levels of phosphorylation of 14 phosphoproteins (including protein kinases B and C) after 5 and 15 minutes. Further analysis of ERK1 and 2 and STAT3 phosphorylation showed rapid increases within 1 minute of CTGF exposure that peaked between 5 and 10 minutes then returned to pretreatment levels by 30 minutes. Treatment of HCF with selective inhibitors of Ras, MEK 1/2, and ERK1/2 individually blocked both CTGF induced cell proliferation, and collagen gel contraction. CONCLUSIONS Results from protein kinase screens and selective kinase inhibitors demonstrate Ras/MEK/ERK/STAT3 pathway is required for CTGF signaling in HCF.

Hammerhead ribozyme-mediated knockdown of mRNA for fibrotic growth factors: transforming growth factor-beta 1 and connective tissue growth factor.

Excessive scarring (fibrosis) is a major cause of pathologies in multiple tissues, including lung, liver, kidney, heart, cornea, and skin. The transforming growth factor-β (TGF-β) system has been shown to play a key role in regulating the formation of scar tissue throughout the body. Furthermore, connective tissue growth factor (CTGF) has been shown to mediate most of the fibrotic actions of TGF-β, including stimulation of synthesis of extracellular matrix and differentiation of fibroblasts into myofibroblasts. Currently, no approved drugs selectively and specifically regulate scar formation. Thus, there is a need for a drug that selectively targets the TGF-β cascade at the molecular level and has minimal off-target side effects. This chapter focuses on the design of hammerhead ribozymes, measurement of kinetic activity, and assessment of knockdown mRNAs of TGF-β and CTGF in cell cultures.

Topical application of recombinant platelet-derived growth factor increases the rate of healing and the level of proteins that regulate this response.

A bipedicle ischaemic rat skin flap model was used to study the effects of daily topical applications of platelet‐derived growth factor (PDGF) on the healing of ischaemic wounds. Levels of tumour necrosis factor‐alpha (TNFA), interleukin 1‐beta (IL1B) and both the latent and active forms of matrix metalloproteinase 2 (MMP2) and 9 (MMP9) were measured. Full‐thickness wounds were made on a total of 72 adult male Sprague–Dawley rats. Each group of 18 rats with normal and ischaemic wounds received either vehicle or 0·01% recombinant PDGF‐BB. Additional applications were made on the wounds on a daily basis. Wound areas were measured at 0, 1, 3, 5, 7 9 and 13 days after wounding. Ischaemia caused a delay in wound healing as well as an increase in TNFA, IL1B and both the pro and active forms of MMP2 and MMP9. PDGF accelerated the rate of wound healing in both normal and ischaemic wounds and negated the effect of ischaemia. PDGF reduced the TNFA concentration in both normal and ischaemic wounds, and the rate of wound healing closely resembled the pattern of TNFA protein expression. PDGF also reduced both the magnitude and duration of the increases in IL1B and both the pro and active forms of MMP2 and MMP9 induced by ischaemia.