Iron-oxide minerals in the human tissues.

Iron is critically important and highly regulated trace metal in the human body. However, in its free ion form, it is known to be cytotoxic; therefore, it is bound to iron storing protein, ferritin. Ferritin is a key regulator of body iron homeostasis able to form various types of minerals depending on the tissue environment. Each mineral, e.g. magnetite, maghemite, goethite, akaganeite or hematite, present in the ferritin core carry different characteristics possibly affecting cells in the tissue. In specific cases, it can lead to disease development. Widely studied connection with neurodegenerative conditions is widely studied, including Alzheimer disease. Although the exact ferritin structure and its distribution throughout a human body are still not fully known, many studies have attempted to elucidate the mechanisms involved in its regulation and pathogenesis. In this review, we try to summarize the iron uptake into the body. Next, we discuss the known occurrence of ferritin in human tissues. Lastly, we also examine the formation of iron oxides and their involvement in brain functions.

Topical vanadate enhances the repair of median laparotomy incisions.

BACKGROUND: There are over two million laparotomies performed in the United States each year with an incisional hernia rate between 2% and 11%. A total of 100,000 ventral hernia repairs are undertaken each year with recurrences as high as 50%. MATERIALS AND METHODS: Full thickness midline fascia incisions from the xiphoid to the pubic symphysis were made in rats. The fascia and/or muscular layer was sutured closed and a gel with 300 µM of sodium orthovanadate or saline was placed over the suture line with the skin closed over it. On day 10, 1-cm strips from the superior, middle, and inferior regions of the abdominal wall were tested for breaking strength and processed for histology. RESULTS: The mean wound breaking strength of vanadate-treated wounds was 18.6 ± 2.7 N compared with 9.4 ± 3.6 N for controls (P < 0.0001). Similar quantities of granulation tissue were deposited in treated and control wounds. Fine green birefringence patterns, characteristic of immature connective tissue, were seen in control samples viewed with polarized light. In contrast, vanadate-treated wounds showed thick yellow-orange birefringence patterns characteristics of more mature connective tissue. Using α-smooth muscle actin immunostaining, myofibroblasts were prominent in control incisions, but few were identified in vanadate-treated incisions. CONCLUSIONS: In rat laparotomy wounds, a single application of vanadate increases wound breaking strength, through enhanced connective tissue organization. These combined data suggest topical application of vanadate immediately after fascial closure will increase wound strength, possibly reducing hernia recurrences in the repaired abdominal wall.

A mathematical model of collagen lattice contraction.

Two mathematical models for fibroblast-collagen interaction are proposed which reproduce qualitative features of fibroblast-populated collagen lattice contraction. Both models are force based and model the cells as individual entities with discrete attachment sites; however, the collagen lattice is modelled differently in each model. In the collagen lattice model, the lattice is more interconnected and formed by triangulating nodes to form the fibrous structure. In the collagen fibre model, the nodes are not triangulated, are less interconnected, and the collagen fibres are modelled as a string of nodes. Both models suggest that the overall increase in stress of the lattice as it contracts is not the cause of the reduced rate of contraction, but that the reduced rate of contraction is due to inactivation of the fibroblasts.

Mast cells prevent dexamethasone-induced cell death of cultured fibroblasts: relationship to gap junctional intercellular communications.

BACKGROUND: Dexamethasone, a common therapy for reducing hypertrophic scar, sometimes fails. However, in cell culture, all dexamethasone-treated fibroblasts die. In co-cultures, gap junction intercellular communications between mast cells and fibroblasts promote profibrotic activities. Does the co-culture of mast cells with fibroblasts prevent dexamethasone-induced fibroblast death? METHODS: Survival of fibroblasts co-cultured with RMC-1 cells, a rat mast cell line, receiving dexamethasone was studied. RMC-1 cells pretreated with a secretagogue that degranulated mast cells and/or with a long-acting gap junction intercellular communications inhibitor were compared to untreated RMC-1 cells co-cultured with fibroblasts and dexamethasone. RESULTS: Fibroblasts alone treated with dexamethasone all died in 3 hours. Fibroblasts co-cultured with intact RMC-1 cells or with degranulated RMC-1 cells in dexamethasone all survived. No fibroblasts survived, co-cultured with RMC-1 cells unable to form gap junction intercellular communications with fibroblasts. CONCLUSIONS: Dexamethasone-treated fibroblasts, forming gap junction intercellular communications with mast cells, may explain why dexamethasone therapy sometimes fails. Gap junction intercellular communications between scar mast cells and fibroblasts or myofibroblasts apparently blocks the death of these cell populations. Preventing gap junction intercellular communications between mast cells and fibroblasts by including anti-gap junction intercellular communication agents may enhance the effectiveness of steroid therapy in treating excessive scarring.

Discovery of 505-million-year old chitin in the basal demosponge Vauxia gracilenta.

Sponges are probably the earliest branching animals, and their fossil record dates back to the Precambrian. Identifying their skeletal structure and composition is thus a crucial step in improving our understanding of the early evolution of metazoans. Here, we present the discovery of 505-million-year-old chitin, found in exceptionally well preserved Vauxia gracilenta sponges from the Middle Cambrian Burgess Shale. Our new findings indicate that, given the right fossilization conditions, chitin is stable for much longer than previously suspected. The preservation of chitin in these fossils opens new avenues for research into other ancient fossil groups.

Development of novel treatment options for patients with haemophilia.

UNLABELLED: Treatment of haemophilia has vastly improved over the last years, but many needs are still unmet. Baxter is continuously pursuing the aim to provide new therapeutic options to patients with haemophilia and to their treating physicians. In fact, there are several opportunities to improve existing therapies, e.g., by new indications for existing products, the introduction of new products, and by novel therapeutic approaches other than factor replacement. Among these, Baxter is working on a number of innovations, such as pharmacokinetics-tailored factor VIII prophylaxis, bypassing agent prophylaxis with FEIBA in inhibitor patients, development of a longer acting pegylated recombinant FVIII, a new recombinant factor IX, a new recombinant factor FVIIa, the first recombinant von Willebrand factor, recombinant ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) as well as gene therapy to cure haemophilia B. CONCLUSION: Baxter is truly committed to the benefit for the patient, and therefore engaged in providing a more and more individualized treatment, in increasing efficiency of current products, in developing new products and new approaches with added value.

Cell-populated collagen lattice contraction model for the investigation of fibroblast collagen interactions.

The fibroblast-populated collagen lattice (FPCL) was intended to act as the dermal component for "skin-equivalent" or artificial skin developed for skin grafting burn patients. The "skin-equivalent" was clinically unsuccessful as a skin graft, but today it is successfully used as a dressing for the management of chronic wounds. The FPCL has, however, become an instrument for investigating cell-connective tissue interactions within a three-dimensional matrix. Through the capacity of cell compaction of collagen fibrils, the FPCL undergoes a reduction in volume referred to as lattice contraction. Lattice contraction proceeds by cell-generated forces that reduce the water mass between collagen fibers, generating a closer relationship between collagen fibers. The compaction of collagen fibers is responsible for the reduction in the FPCL volume. Cell-generated forces through the linkage of collagen fibers with fibroblast's cytoskeletal actin-rich microfilament structures are responsible for the completion of the collagen matrix compaction. The type of culture dish used to cast FPCL as well as the cell number will dictate the mechanism for compacting collagen matrices. Fibroblasts, at moderate density, cast as an FPCL within a petri dish and released from the surface of the dish soon after casting compact collagen fibers through cell tractional forces. Fibroblasts at moderate density cast as an FPCL within a tissue culture dish and not released for 4 days upon release show rapid lattice contraction through a mechanism of cell contraction forces. Fibroblasts at high density cast in an FPCL within a petri dish, released from the surface of the dish soon after casting, compact a collagen lattice very rapidly through forces related to cell elongation. The advantage of the FPCL contraction model is the study of cells in the three-dimensional environment, which is similar to the environment from which these cells were isolated. In this chapter methods are described for manufacturing collagen lattices, which assess the three forces involved in compacting and/or organizing collagen fibrils into thicker collagen fibers. The clinical relevance of the FPCL contraction model is related to advancing our understanding of wound contraction and scar contracture.

Through gap junction communications, co-cultured mast cells and fibroblasts generate fibroblast activities allied with hypertrophic scarring.

BACKGROUND: The prominent inflammatory cell identified in excessive scarring is the mast cell. Hypertrophic scar exhibits myofibroblasts derived from the transformation of fibroblasts, increased collagen synthesis, and stationary nonmigratory resident cells. The co-culture of fibroblasts with an established rat mast cell line (RMC-1) was used to explore the hypothesis of whether mast cells through gap junctional intercellular communications guide fibroblasts in promoting excessive scarring. METHODS: Human dermal fibroblasts were cultured alone or co-cultured with RMC-1 cells as is or with either blocked gap junctional intercellular communications or devoid of cytoplasmic granules. Collagen synthesis was analyzed by dot blot analysis; immunohistology identified myofibroblasts, and a cell migration assay measured fibroblast locomotion. RESULTS: Fibroblasts co-cultured with RMC-1 cells transformed into myofibroblasts, had increased collagen synthesis, and showed retarded cell migration. In contrast, RMC-1 cells unable to form gap junctional intercellular communications were similar to fibroblasts alone, failing to promote these activities. Degranulated RMC-1 cells were as effective as intact RMC-1 cells. CONCLUSIONS: Mast cells induce fibroblast activities associated with hypertrophic scarring through gap junctional intercellular communications. Eliminating the mast cell or its gap junctional intercellular communications with fibroblasts may be a possible approach in preventing hypertrophic scarring or reducing fibrotic conditions.

Capsular contracture after breast reconstruction: collagen fiber orientation and organization.

BACKGROUND: Breast implant capsular contracture is a common complication of implant-based breast reconstruction. To develop nonsurgical interventions to combat breast capsular contractures, a clearer understanding of the process is required. Comparing breast implant-related capsular contracture to the fibrotic scarring process, the hypothesis is that these processes differ with regard to the compaction of collagen fibers within the connective tissue matrix. METHODS: Morphologic differences in the connective tissue matrix by light, polarized light, and fluorescence microscopy documents these differences. Discarded Baker grade II and III periimplant capsules harvested during routine breast reconstructive operations were used for the evaluation. RESULTS: Within severe breast capsule contractures, light microscopy revealed the absence of mast cells, whereas polarized light microcopy showed that collagen fiber bundles were consolidated into thick cable-like structures. In less severe breast capsules, mast cells were present, whereas thick cable-like collagen structures were absent. By fluorescence microscopy, fibroblast populations associated with severe contractures were oriented perpendicular to the long axis, suggesting a spiral orientation in the compaction of these cable-like structures. These findings were absent in less severe contractures. CONCLUSIONS: To the authors' knowledge, these histologic findings in breast implant capsules are unreported and unique when compared with other fibrotic contractures. Elucidating the biological mechanisms involved in the reorganization of collagen fiber bundles that lead to implant-related capsular contracture is a critical step for developing strategies to treat and control breast capsule contractures.

A Snapshot of Direct Cell-Cell Communications in Wound Healing and Scarring.

SIGNIFICANCE: The repair of wounds usually terminates with a scar. The healing from a severe tissue loss can create a new clinical problem, excessive scarring. Approaches to prevent excessive scarring will optimize the repair process. Controlling gap-junction communications between cells and/or the transport of the proteins that form gap junctions offers new approaches for controlling this problem. RECENT ADVANCES: Gap-junctional intercellular communication (GJIC) requires hemichannels, connexon structures, embedded in the plasma membrane of coupled cells. The connexon is composed of six proteins from the connexin (Cx) family. The docking of connexons between the neighboring cells forms a gated channel, where small molecules can pass directly between the cytoplasm of cells. In wound repair, GJIC between fibroblasts in granulation tissue advances wound repair. Also, the GJIC between mast cells and fibroblasts during the remodeling phase of repair may explain how mast cells promote excessive scarring. In addition, Cx can affect transforming growth factor beta (TGF-ß) intracellular signaling through its shared binding site on microtubules within fibroblasts. CRITICAL ISSUES: Can excessive scarring be controlled through limiting the local amassing of mast cells or preventing their interactions with wound fibroblasts through GJIC? FUTURE DIRECTIONS: The prevention of the accumulation of mast cells in granulation tissue or interfering with their communications via GJIC with fibroblasts offers new approaches for preventing excess scarring. The association of Cx with microtubules altering TGF-ß signaling presents a new target for improving the quality of repair as well as the deposition of unnecessary fibrosis.

Thymosin ß4 affecting the cytoskeleton organization of the myofibroblasts.

In previous studies, granulation tissue from subcutaneous sponge implants in rats receiving thymosin ß4, a 43-amino acid actin-binding protein that advances wound repair, produced the unexpected absence of myofibroblast populations, along with uniform organized collagen fibers within the newly deposited connective tissue matrix. This result raised the question of whether the Tß4 effect on blocking fibroblasts transformation into myofibroblasts a direct or indirect one. We report here work in progress to address this question. When human dermal fibroblasts are plated at low density, upon reaching confluence, they all express α smooth muscle actin (αSMA) within their cytoplasmic stress fibers, morphologically defining them as myofibroblasts. Treating low-density plated fibroblasts with Tß4 prevents their expression of αSMA, as well as the generation an uneven distribution of microtubules within the cytoplasm. The speculation is that Tß4 disruption of the distribution of microtubules alters the TGF-ß-Smad signaling pathway, thus blocking fibroblast transformation into myofibroblasts.

BAX 855, a PEGylated rFVIII product with prolonged half-life. Development, functional and structural characterisation.

A longer acting recombinant FVIII is expected to serve patients' demand for a more convenient prophylactic therapy. We have developed BAX 855, a PEGylated form of Baxter's rFVIII product ADVATE™ based on the ADVATE™ manufacturing process. The conjugation process for preparing BAX 855 uses a novel PEG reagent. The production process was adjusted to yield a rFVIII conjugate with a low PEGylation degree of about 2 moles PEG per FVIII molecule. This optimised modification degree resulted in an improved PK profile for rFVIII without compromising its specific activity. PEGylation sites were identified by employing various HPLC- and MS-based methods. These studies not only indicated that about 60% of the PEG chains are localised to the B-domain, which is cleaved off upon physiological activation during the coagulation process, but also demonstrated an excellent lot to lot consistency with regard to PEGylation site distribution. Detailed biochemical characterization further showed that PEGylated FVIII retained all the physiological functions of the FVIII molecule with the exception of binding to the LRP clearance receptor which was reduced for BAX 855 compared to ADVATE™. This might provide an explanation for the prolonged circulation time of BAX 855 as reduced receptor binding might slow-down clearance. Preclinical studies showed improved pharmacokinetic behaviour and clinically relevant prolonged efficacy compared to ADVATE™ without any signs of toxicity or elevated immunogenicity. The comprehensive preclinical data package formed the basis for approval of the phase 1 clinical study by European authorities which started in 2011.

Evidence that translocation of collagen fibril segments plays a role in early intrinsic tendon repair.

BACKGROUND: Severed tendon repair advances with either a scar through extrinsic repair or regeneration through intrinsic repair. The authors examined whether intrinsic tendon repair reintroduces embryonic fibrillogenesis, whereby preformed collagen fibril segments are incorporated into growing collagen fibers at wound edges. METHODS: Isolated tendons from 10-day-old chicken embryos were suspended in 1 mg/ml of the antibiotic gentamicin for 90 days, which released fibril segments that were fluorescently tagged with rhodamine. Tendons isolated from 14-day-old chicken embryos were wounded to half their diameter and then maintained as explants in stationary organ culture. Fluorescent-tagged fibril segments were introduced to wounded tendon explants in the presence of high concentrations of neomycin, an antibiotic; cycloheximide, a protein synthesis inhibitor; cytochalasin D, a disruptor of microfilaments; and colchicine, a disruptor of microtubules. At 24 hours, explants were viewed by means of fluorescent microscopy. RESULTS: Untreated, wounded tendon explants showed the translocation of fluorescent-tagged fibril segments from the explant surface to accumulation at wound edges. In the presence of high concentrations of neomycin, cytochalasin D, or colchicine, fluorescent-tagged fibril segments failed to accumulate at wound edges and were retained on the explant surface. Inhibition of protein synthesis by cycloheximide did not alter the accumulation of fluorescent-tagged fibril segments at wound edges. CONCLUSIONS: Inhibiting fluorescent-tagged fibril segment accumulation by antibiotics is consistent with their role in releasing fibril segments. Experimental findings show fibril segment translocation and accumulation at wound edges involves microfilaments and microtubules, but not protein synthesis. The experiments support the hypothesis that intrinsic tendon repair advances through the incorporation of fibril segments at wound edges.

Collagen Organization Critical Role in Wound Contraction.

BACKGROUND: Open wound closure by wound contraction produces a healed defect made up mostly of dermis. Generating thicker collagen fibers condenses granulation tissue, which pulls surrounding skin into the defect. THE PROBLEM: What is the mechanism for open wound contraction? Is it through the generation of contractile force using sustained myosin ATPase, thus causing cell contraction or by rapid myosin ATPase that condenses collagen fibrils into fibers? BASIC/CLINICAL SCIENCE ADDRESSED: The mechanism for wound contraction is not often debated after the discovery of the myofibroblast. Myofibroblasts are the major cell phenotype in maturing granulation tissue. It is concluded, not quite accurately, that myofibroblasts are responsible for wound contraction. As wound contraction progresses, polarized light microscopy reveals birefringence patterns associated with ever-increasing thickening of collagen fibers. Collagen fibers thicken by eliminating water between fibrils. Wound contraction requires collagen synthesis and granulation tissue compaction. Both myofibroblasts and fibroblasts synthesize collagen, but fibroblasts, not myofibroblasts, compact collagen. Free-floating fibroblast-populated collagen lattices (FPCL) contract by rapid myosin ATPase, thus resulting in thicker collagen fibers by elongated fibroblasts. The release of an attached FPCL, using sustained myosin ATPase, produces rapid lattice contraction, now populated with contracted myofibroblasts in the absence of thick collagen fibers. DISCUSSION: In vivo and in vitro studies show that rapid myosin ATPase is the motor for wound contraction. Myofibroblasts maintain steady mechano-tension through sustained myosin ATPase, which generates cell contraction forces that fail to produce thicker collagen fibers. The hypothesis is that cytoplasmic microfilaments pull collagen fibrils over the fibroblast's plasma membrane surface, bringing collagen fibrils in closer contact with one another. The self-assembly nature of collagen fixes collagen fibrils in regular arrays generating thicker collagen fibers. CONCLUSION: Wound contraction progresses through fibroblasts generating thicker collagen fibers, using tractional forces; rather than by myofibroblasts utilizing cell contraction forces.

Demonstrating collagen tendon fibril segments involvement in intrinsic tendon repair.

Severed tendons can undergo regenerative healing, intrinsic tendon repair. Fibrillogenesis of chick tendon involves "collagen fibril segments" (CFS), which are the building blocks of collagen fibers that make up tendon fascicles. The CFS are 10.5 micron in length, composed of tropocollagen monomers arranged in parallel arrays. Rather than incorporating single tropocollagen molecules into growing collagen fibers, incorporating large CFS units is the mechanism for generating collagen fibers. Is intrinsic tendon repair through the reestablishment of tendon embryogenesis? Gentamicin treated 10-day-old chick embryo tendons released CFS were fluorescently tagged with Rhodamine (Rh). Organ cultured severed 14-day-old embryo tendon explants received Rh tagged CFS. At day 4 auto fluorescent tagged CFS were identified at the severed tendon ends by fluorescent microscopy. Accumulation of fluorescent tagged CFS was exclusively localized to the severed ends of tendon explants. Parallels between collagen fiber growth during embryonic fibrillogenesis and tendon repair reveal CFS incorporation is responsible for collagen fibers growth. CFS incorporation into frayed collagen fibers from severed tendons is the proposed mechanism for intrinsic tendon repair, which is an example of regenerative repair.

Fibroblast expression of α-smooth muscle actin, α2ß1 integrin and αvß3 integrin: influence of surface rigidity.

Open wound contraction necessitates cell and connective tissue interactions, that produce tension. Investigating fibroblast responses to tension utilizes collagen coated polyacrylamide gels with differences in stiffness. Human foreskin fibroblasts were plated on native type I collagen-coated polyacrylamide gel cover slips with different rigidities, which were controlled by bis-acrylamide concentrations. Changes in alpha smooth muscle actin (αSMA), α2ß1 integrin (CD49B) and αvß3 integrin (CD-51) were documented by immuno-histology and Western blot analysis. Cells plated on rigid gels were longer, and expressed αvß3 integrin and αSMA within cytoplasmic stress fibers. In contrast, cells on flexible gels were shorter, expressed α2ß1 integrin and had fine cytoskeletal microfilaments without αSMA. Increased tension changed the actin makeup of the cytoskeleton and the integrin expressed on the cell's surface. These in vitro findings are in agreement with the tension buildup as an open wound closes by wound contraction. It supports the notion that cells under minimal tension in early granulation tissue express α2ß1 integrin, required for organizing fine collagen fibrils into thick collagen fibers. Thicker fibers create a rigid matrix, generating more tension. With increased tension cytoskeletal stress fibers develop that contain αSMA and αvß3 integrin that replaces α2ß1 integrin, consistent with cell switching from collagen to non-collagen proteins interactions.

Rat mast cells enhance fibroblast proliferation and fibroblast-populated collagen lattice contraction through gap junctional intercellular communications.

BACKGROUND: Mast cells' association with fibrosis is known, but the mechanics of that association are unclear. The hypothesis is that mast cells promote fibroblast profibrotic activities through heterocellular gap junctional intercellular communications. Casting populated collagen lattices with both human mastocytoma cell line (HMC-1), an established mast cell line, and fibroblasts enhances lattice contraction via gap junctional intercellular communications. Unfortunately, in monolayer culture, HMC-1 cells and fibroblasts do not form heterocellular gap junctional intercellular communications. Freshly isolated rat peritoneal mast cells, however, establish these communications with fibroblasts in monolayer culture. Isolated rat peritoneal mast cells, however, survive only 7 days. Establishing a rat mast cell line that grows in the same medium as fibroblasts advances the study of mast cell-fibroblast interactions. HMC-1 cells thrive without supplements, suggesting that they release the factor(s) necessary for their viability. Spent HMC-1 medium may contain the factor(s) that generate a viable rat mast cell line. METHODS: Rat peritoneal-isolated mast cells grew in culture medium containing spent HMC-1 medium for 4 weeks. At 4 weeks, rat mast cells (RMC-1) were successfully maintained in Dulbecco's Modified Eagle Medium with 10% serum. RESULTS: RMC-1 cells formed heterocellular gap junctional intercellular communications with fibroblasts, enhancing both fibroblast proliferation and co-cultured RMC-1/fibroblast/populated collagen lattice contraction. Enhanced fibroblast proliferation and lattice contraction failed to occur by including RMC-1 cells unable to establish gap junctional intercellular communications with fibroblasts, but cell proliferation was not affected by including degranulated RMC-1 cells. CONCLUSION: Heterocellular gap junctional intercellular communications with mast cells increase in fibroblast proliferation and fibroblast PCL contraction, two hypertrophic scar fibroblast activities.

Recombinant ADAMTS13 normalizes von Willebrand factor-cleaving activity in plasma of acquired TTP patients by overriding inhibitory antibodies.

BACKGROUND: Severe deficiency of the von Willebrand factor (VWF)-cleaving protease ADAMTS13 as observed in acquired thrombotic thrombocytopenic purpura (TTP) is caused by inhibitory and non-inhibitory autoantibodies directed against the protease. Current treatment with plasma exchange is considered to remove circulating antibodies and to concurrently replenish the deficient enzyme. OBJECTIVES: To explore the use of recombinant ADAMTS13 (rADAMTS13) as a potential therapeutic agent in acquired TTP, we investigated its efficacy in normalizing VWF-cleaving activity in the presence of ADAMTS13 inhibitors. METHODS: Thirty-six plasma samples from TTP patients were adjusted to predefined inhibitor titers, and recovery of ADAMTS13 activity was analyzed following supplementation with rADAMTS13. RESULTS: We showed a linear relation between the inhibitor titer measured and effective rADAMTS13 concentration necessary for reconstitution of VWF-cleaving activity in the presence of neutralizing autoantibodies. CONCLUSIONS: Our results support the further investigation of the potential therapeutic applicability of rADAMTS13 as an adjunctive therapy in acquired TTP.

Modulatory effects of connexin-43 expression on gap junction intercellular communications with mast cells and fibroblasts.

The influence of mast cells upon aberrant wound repair and excessive fibrosis has supportive evidence, but the mechanism for these mast cell activities is unclear. It is proposed that heterocellular gap junction intercellular communication (GJIC) between fibroblasts and mast cells directs some fibroblast activities. An in vitro model was used employing a rodent derived peritoneal mast cell line (RMC-1) and human dermal derived fibroblasts. The influence of the expression of the gap junction channel structural protein, connexin 43 (Cx-43) on heterocellular GJIC, the expression of microtubule ß-tubulin and microfilament α smooth muscle actin (SMA) were investigated. The knockdown of Cx-43 by siRNA in RMC-1 cells completely blocked GJIC between RMC-1 cells. SiRNA knockdown of Cx-43 within fibroblasts only dampened GJIC between fibroblasts. It appears Cx-43 is the only expressed connexin (Cx) in RMC-1 cells. Fibroblasts express other Cxs that participate in GJIC between fibroblasts in the absence of Cx-43 expression. Heterocellular GJIC between RMC-1 cells and fibroblasts transformed fibroblasts into myofibroblasts, expressing α SMA within cytoplasmic stress fibers. The knockdown of Cx-43 in RMC-1 cells increased ß-tubulin expression, but its knockdown in fibroblasts reduced ß-tubulin expression. Knocking down the expression of Cx-43 in fibroblasts limited αSMA expression. Cx-43 participation is critical for heterocellular GJIC between mast cells and fibroblasts, which may herald a novel direction for controlling fibrosis.