Multi-color palette of fluorescent proteins for imaging the tumor microenvironment of orthotopic tumorgraft mouse models of clinical pancreatic cancer specimens

Pancreatic-cancer-patient tumor specimens were initially established subcutaneously in NOD/SCID mice immediately after surgery. The patient tumors were then harvested from NOD/SCID mice and passaged orthotopically in transgenic nude mice ubiquitously expressing red fluorescent protein (RFP). The primary patient tumors acquired RFP-expressing stroma. The RFP-expressing stroma included cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Further passage to transgenic nude mice ubiquitously expressing green fluorescent protein (GFP) resulted in tumors that acquired GFP stroma in addition to their RFP stroma, including CAFs and TAMs as well as blood vessels. The RFP stroma persisted in the tumors growing in the GFP mice. Further passage to transgenic nude mice ubiquitously expressing cyan fluorescent protein (CFP) resulted in tumors acquiring CFP stroma in addition to persisting RFP and GFP stroma, including RFP- and GFP-expressing CAFs, TAMs and blood vessels. This model can be used to image progression of patient pancreatic tumors and to visually target stroma as well as cancer cells and to individualize patient therapy.     

A transgenic red fluorescent protein‐expressing nude mouse for color‐coded imaging of the tumor microenvironment

The tumor microenvironment (TME) is critical for tumor growth and progression. We have previously developed color‐coded imaging of the TME using a green fluorescent protein (GFP) transgenic nude mouse as a host. However, most donor sources of cell types appropriate for study in the TME are from mice expressing GFP. Therefore, a nude mouse expressing red fluorescent protein (RFP) would be an appropriate host for transplantation of GFP‐expressing stromal cells as well as double‐labeled cancer cells expressing GFP in the nucleus and RFP in the cytoplasm, thereby creating a three‐color imaging model of the TME. The RFP nude mouse was obtained by crossing non‐transgenic nude mice with the transgenic C57/B6 mouse in which the β‐actin promoter drives RFP (DsRed2) expression in essentially all tissues. In crosses between nu/nu RFP male mice and nu/+ RFP female mice, the embryos fluoresced red. Approximately 50% of the offspring of these mice were RFP nude mice. In the RFP nude mouse, the organs all brightly expressed RFP, including the heart, lungs, spleen, pancreas, esophagus, stomach, duodenum, the male and female reproductive systems; brain and spinal cord; and the circulatory system, including the heart, and major arteries and veins. The skinned skeleton highly expressed RFP. The bone marrow and spleen cells were also RFP positive. GFP‐expressing human cancer cell lines, including HCT‐116‐GFP colon cancer and MDA‐MB‐435‐GFP breast cancer were orthotopically transplanted to the transgenic RFP nude mice. These human tumors grew extensively in the transgenic RFP nude mouse. Dual‐color fluorescence imaging enabled visualization of human tumor–host interaction. The RFP nude mouse model should greatly expand our knowledge of the TME. J. Cell. Biochem. 106: 279–284, 2009. © 2008 Wiley‐Liss, Inc.     

Nestin‐expressing interfollicular blood vessel network contributes to skin transplant survival and wound healing

Using nestin‐driven green fluorescent protein (ND‐GFP) transgenic mice, we previously demonstrated an inter‐hair‐follicle blood vessel network that expresses ND‐GFP and appears to originate from ND‐GFP expressing hair‐follicle stem cells. We report here that angiogenesis of transplanted skin or healing wounds originates from this ND‐GFP‐expressing microvasculature network. ND‐GFP‐expressing blood vessels were visualized growing from the ND‐GFP‐expressing hair‐follicle stem cell area and re‐establishing the dermal microvasculature network after skin transplantation or wound healing. When the ND‐GFP stem cell area from the vibrissa (whisker) from ND‐GFP mice was transplanted to transgenic mice ubiquitously expressing RFP, we observed chimeric ND‐GFP‐RFP blood vessels, suggesting the joining of inter‐follicular blood vessel networks from the transplant and host. These observations suggest that the inter‐hair‐follicle blood‐vessel network contributes to skin transplant survival and wound healing. J. Cell. Biochem. 110: 80–86, 2010. © 2010 Wiley‐Liss, Inc.     

荧光标记技术在肿瘤模型研究中的应用

目的利用绿色荧光小鼠和红色荧光蛋白标记肿瘤细胞,建立荧光标记的小鼠肿瘤模型,并建立活体荧光成像和荧光显微镜成像在整体和细胞水平直接观察肿瘤的技术。方法将小鼠B16黑色素瘤细胞接种到绿色荧光蛋白转基因小鼠皮下,建立GFP小鼠肿瘤模型。以红色荧光蛋白作为标记基因导入小鼠黑色素瘤细胞B16细胞,建立稳定表达红色荧光蛋白的细胞株。将表达红色荧光蛋白B16细胞接种到绿色荧光转基因小鼠皮下,建立双荧光小鼠肿瘤模型。用荧光显微镜和活体荧光成像系统检测小鼠肿瘤的发生发展。结果分别建立了GFP小鼠肿瘤模型和双色荧光小鼠肿瘤模型。利用活体荧光影像仪可以观察双色荧光小鼠模型中受体绿色荧光组织和红色荧光移植肿瘤相互融合。利用荧光显微镜,可以观察到肿瘤内绿色荧光标记的来源于受体小鼠的血管和免疫细胞。经香菇多糖刺激的GFP小鼠肿瘤模型的移植瘤组织中,来源于受体小鼠绿色荧光标记的免疫细胞明显多于经生理盐水刺激的对照小鼠。结论利用绿色荧光小鼠和红色荧光RFP标记肿瘤细胞建立荧光标记的小鼠肿瘤模型,采用活体荧光成像仪和荧光显微镜可在整体和细胞水平直接观察肿瘤的生长以及肿瘤与宿主的相互作用。     

In vivo imaging of nuclear-cytoplasmic deformation and partition during cancer cell death due to immune rejection

In this report, we investigated the in vivo cell biology of cancer cells during immune rejection. The use of nestin-driven green fluorescent protein (ND-GFP) transgenic mice as hosts, in which nascent blood vessels express GFP, and implanted dual-color mouse mammary tumor 060562 (MMT) cells, in which the cytoplasm expresses red fluorescent protein (RFP) and the nuclei express GFP, allowed very important novel observations of angiogenesis and subcellular death pathways during immune rejection of a tumor. Nascent blood vessels did not form in the initially-growing mouse mammary tumor in ND-GFP immunocompetent mice. In contrast, in ND-GFP immunodeficient nude mice, numerous GFP-expressing nascent blood vessels grew into the tumor. The results suggest that insufficient nascent tumor angiogenesis was important in tumor rejection. During immune rejection, the cancer cells deformed their cytoplasm and nuclei, which were readily imaged by RFP and GFP, respectively. The nuclear membrane of the cancer cells ruptured, and chromatin extruded during partition of cytoplasm and nuclei. T lymphocytes infiltrated into the initially-growing tumor in the nestin-GFP transgenic immunocompetent mice. The cytotoxic role of the sensitized T lymphocytes was confirmed in vitro when they were co-cultured with MMT cells. The CD8a-positive lymphocytes attached to the cancer cells and caused nuclear condensation, deformation, and partition from their cytoplasm, similar to what occurred in vivo. The color-coded subcellular fluorescence-imaging model of immune rejection of cancer cells can provide a comprehensive system for further testing of immune-based treatment for cancer.     

Development of the transgenic cyan fluorescent protein (CFP)‐expressing nude mouse for “Technicolor” cancer imaging

A major goal for in vivo biology is to develop models which can express multiple colors of fluorescent proteins in order to image many processes simultaneously in real time. Towards this goal, the cyan fluorescent protein (CFP) nude mouse was developed by crossing non‐transgenic nude mice with the transgenic CK/ECFP mouse in which the β‐actin promoter drives expression of CFP in almost all tissues. In crosses between nu/nu CFP male mice and nu/+ CFP female mice, approximately 50% of the embryos fluoresced blue. In the CFP nude mice, the pancreas and reproductive organs displayed the strongest fluorescent signals of all internal organs which vary in intensity. Orthotopic implantation of XPA‐1 human pancreatic cancer cells expressing red fluorescent protein (RFP); or green fluorescent protein (GFP) in the nucleus and RFP in the cytoplasm, was performed in female nude CFP mice. Color‐coded fluorescence imaging of these human pancreatic cancer cells implanted into the bright blue fluorescent pancreas of the CFP nude mouse afforded novel insight into the interaction of the pancreatic tumor and the normal pancreas, in particular the strong desmoplastic reaction of the tumor. The naturally enhanced blue fluorescence of the pancreas in the CFP mouse serves as an ideal background for color‐coded imaging of the interaction of implanted cancer cells and the host. The CFP nude mouse will provide unique understanding of the critical interplay between the cancer cells and their microenvironment. J. Cell. Biochem. 107: 328–334, 2009. © 2009 Wiley‐Liss, Inc.     

Ubiquitous expression of the monomeric red fluorescent protein mcherry in transgenic mice

The use of the green fluorescent protein (GFP) to label specific cell types and track gene expression in animal models, such as mice, has evolved to become an essential tool in biological research. Transgenic animals expressing genes of interest linked to GFP, either as a fusion protein or transcribed from an internal ribosomal entry site (IRES) are widely used. Enhanced GFP (eGFP) is the most common form of GFP used for such applications. However, a red fluorescent protein (RFP) would be highly desirable for use in dual‐labeling applications with GFP derived fluorescent proteins, and for deep in vivo imaging of tissues. Recently, a new generation of monomeric (m)RFPs, such as monomeric (m)Cherry, has been developed that are potentially useful experimentally. mCherry exhibits brighter fluorescence, matures more rapidly, has a higher tolerance for N‐terminal fusion proteins, and is more photostable compared with its predecessor mRFP1. mRFP1 itself was the first true monomer derived from its ancestor DsRed, an obligate tetramer in vivo. Here, we report the successful generation of a transgenic mouse line expressing mCherry as a fluorescent marker, driven by the ubiquitin‐C promoter. mCherry is expressed in almost all tissues analyzed including pre‐ and post‐implantation stage embryos, and white blood cells. No expression was detected in erythrocytes and thrombocytes. Importantly, we did not encounter any changes in normal development, general physiology, or reproduction. mCherry is spectrally and genetically distinct from eGFP and, therefore, serves as an excellent red fluorescent marker alone or in combination with eGFP for labelling transgenic animals. genesis 48:723–729, 2010. © 2010 Wiley‐Liss, Inc.     

Laser Scanning Cytometry for selection of green fluorescent protein transgenic mice using small number of blood cells

A Laser Scanning Cytometry-based method was developed for identification of transgenic mice expressing green fluorescent protein (GFP) using minute amounts of peripheral blood. The difference between the autofluorescence of cells not expressing GFP and the fluorescence of GFP expressing cells after excitation with Ar-ion laser (wavelength 488 nm) and detection of emitted fluorescent light in the green channel was high enough for unambiguous identification of the GFP expressing mice. The sensitivity of this method was estimated 1:10(4) for detection of rare GFP expressing cells under the conditions used. This sensitivity should be sufficient for many studies on microchimerism. Because of the possibility for relocation of the cells, this method will be particularly useful for characterizing the cells with high GFP expression using other markers of cell phenotype or conventional morphological analysis.     

Embryonic stem cells and transgenic mice ubiquitously expressing a tau-tagged green fluorescent protein

We have generated embryonic stem (ES) cells and transgenic mice carrying a tau-tagged green fluorescent protein (GFP) transgene under the control of a powerful promoter active in all cell types including those of the central nervous system. GFP requires no substrate and can be detected in fixed or living cells so is an attractive genetic marker. Tau-tagged GFP labels subcellular structures, including axons and the mitotic machinery, by binding the GFP to microtubules. This allows cell morphology to be visualized in exquisite detail. We test the application of cells derived from these mice in several types of cell-mixing experiments and demonstrate that the morphology of tau-GFP-expressing cells can be readily visualized after they have integrated into unlabeled host cells or tissues. We anticipate that these ES cells and transgenic mice will prove a novel and powerful tool for a wide variety of applications including the development of neural transplantation technologies in animal models and fundamental research into axon pathfinding mechanisms. A major advantage of the tau-GFP label is that it can be detected in living cells and labeled cells and their processes can be identified and subjected to a variety of manipulations such as electrophysiological cell recording.     

Afp::mCherry, a red fluorescent transgenic reporter of the mouse visceral endoderm

Live imaging of genetically encoded fluorescent protein reporters is increasingly being used to investigate details of the cellular behaviors that underlie the large-scale tissue rearrangements that shape the embryo. However, the majority of mouse fluorescent reporter strains are based on the green fluorescent protein (GFP). Mouse reporter strains expressing fluorescent colors other than GFP are therefore valuable for co-visualization studies with GFP, where relative positioning and relationship between two different tissues or compartments within cells are being investigated. Here, we report the generation and characterization of a transgenic Afp::mCherry mouse strain in which cis-regulatory elements from the Alpha-fetoprotein (Afp) locus were used to drive expression of the monomeric Cherry red fluorescent protein. The Afp::mCherry transgene is based on and recapitulates reporter expression of a previously described Afp::GFP strain. However, we note that perdurance of mCherry protein is not as prolonged as GFP, making the Afp::mCherry line a more faithful reporter of endogenous Afp expression. Afp::mCherry transgenic mice expressed mCherry specifically in the visceral endoderm and its derivatives, including the visceral yolk sac, gut endoderm, fetal liver, and pancreas of the embryo. The Afp::mCherry reporter was also noted to be expressed in other documented sites of Afp expression including hepatocytes as well as in pancreas, digestive tract, and brain of postnatal mice.     

Quantum dots spectrally distinguish multiple species within the tumor milieu in vivo

A solid tumor is an organ composed of cancer and host cells embedded in an extracellular matrix and nourished by blood vessels. A prerequisite to understanding tumor pathophysiology is the ability to distinguish and monitor each component in dynamic studies. Standard fluorophores hamper simultaneous intravital imaging of these components. Here, we used multiphoton microscopy techniques and transgenic mice that expressed green fluorescent protein, and combined them with the use of quantum dot preparations. We show that these fluorescent semiconductor nanocrystals can be customized to concurrently image and differentiate tumor vessels from both the perivascular cells and the matrix. Moreover, we used them to measure the ability of particles of different sizes to access the tumor. Finally, we successfully monitored the recruitment of quantum dot-labeled bone marrow-derived precursor cells to the tumor vasculature. These examples show the versatility of quantum dots for studying tumor pathophysiology and creating avenues for treatment.     

A color-coded orthotopic nude-mouse treatment model of brain-metastatic paralyzing spinal cord cancer that induces angiogenesis and neurogenesis

Objective: Cancer of the spinal cord is highly malignant and often leads to paralysis and death. A realistic mouse model would be an important benefit for the better understanding and treatment of spinal cord glioma.
Materials and methods: To develop an imageable, patient-like model of this disease, U87 human glioma tumour fragments (expressing red fluorescent protein), were transplanted by surgical orthotopic implantation into the spinal cord of nontransgenic nude mice or transgenic nude mice expressing nestin-driven green fluorescent protein (ND-GFP). In ND-GFP mice, GFP is expressed in nascent blood vessels and neural stem cells. The animals were treated with temozolomide or vehicle control.
Results: The intramedullary spinal cord tumour grew at the primary site, caused hind-limb paralysis and also metastasized to the brain. Temozolomide inhibited tumour growth ( P  < 0.01) and prevented metastasis, as well as prevented paralysis in four mice and delayed paralysis in two mice of the six tested ( P  = 0.005). In the ND-GFP-expressing host, ND-GFP cells staining positively for neuronal class III-β-tubulin or CD31, surrounded the tumour. These results suggest that the tumour stimulated both neurogenesis and angiogenesis, respectively.
Conclusion: A patient-like model of spinal cord glioma was thus developed, which can be used for the discovery of new agents, including those that inhibit invasion and metastasis of the disease as well as those that prevent paralysis.     

Movement of protein and macromolecules between host plants and the parasitic weed Phelipanche aegyptiaca Pers.

Little is known about the translocation of proteins and other macromolecules from a host plant to the parasitic weed Phelipanche spp. Long-distance movement of proteins between host and parasite was explored using transgenic tomato plants expressing green fluorescent protein (GFP) in their companion cells. We further used fluorescent probes of differing molecular weights to trace vascular continuity between the host plant and the parasite. Accumulation of GFP was observed in the central vascular bundle of leaves and in the root phloem of transgenic tomato plants expressing GFP under the regulation of AtSUC2 promoter. When transgenic tomato plants expressing GFP were parasitized with P. aegyptiaca, extensive GFP was translocated from the host phloem to the parasite phloem and accumulated in both Phelipanche tubercles and shoots. No movement of GFP to the parasite was observed when tobacco plants expressing GFP targeted to the ER were parasitized with P. aegyptiaca. Experiments using fluorescent probes of differing molecular weights to trace vascular continuity between the host plant and the parasite demonstrated that Phelipanche absorbs dextrans up to 70 kDa in size from the host and that this movement can be bi-directional. In the present study, we prove for the first time delivery of proteins from host to the parasitic weed P. aegyptiaca via phloem connections, providing information for developing parasite resistance strategies.     

The Murine Stem Cell Virus Promoter Drives Correlated Transgene Expression in the Leukocytes and Cerebellar Purkinje Cells of Transgenic Mice

The murine stem cell virus (MSCV) promoter exhibits activity in mouse hematopoietic cells and embryonic stem cells. We generated transgenic mice that expressed enhanced green fluorescent protein (GFP) under the control of the MSCV promoter. We obtained 12 transgenic founder mice through 2 independent experiments and found that the bodies of 9 of the founder neonates emitted different levels of GFP fluorescence. Flow cytometric analysis of circulating leukocytes revealed that the frequency of GFP-labeled leukocytes among white blood cells ranged from 1.6% to 47.5% across the 12 transgenic mice. The bodies of 9 founder transgenic mice showed various levels of GFP expression. GFP fluorescence was consistently observed in the cerebellum, with faint or almost no fluorescence in other brain regions. In the cerebellum, 10 founders exhibited GFP expression in Purkinje cells at frequencies of 3% to 76%. Of these, 4 mice showed Purkinje cell-specific expression, while 4 and 2 mice expressed GFP in the Bergmann glia and endothelial cells, respectively. The intensity of the GFP fluorescence in the body was relative to the proportion of GFP-positive leukocytes. Moreover, the frequency of the GFP-expressing leukocytes was significantly correlated with the frequency of GFP-expressing Purkinje cells. These results suggest that the MSCV promoter is useful for preferentially expressing a transgene in Purkinje cells. In addition, the proportion of transduced leukocytes in the peripheral circulation reflects the expression level of the transgene in Purkinje cells, which can be used as a way to monitor transgene expression properties in the cerebellum without invasive techniques.     

Generation of Two-color Transgenic Zebrafish Using the Green and Red Fluorescent Protein Reporter Genes gfp and rfp

Two tissue-specific promoters were used to express both green fluorescent protein (GFP) and red fluorescent protein (RFP) in transgenic zebrafish embryos. One promoter (CK), derived from a cytokeratin gene, is active specifically in skin epithelia in embryos, and the other promoter (MLC) from a muscle-specific gene encodes a myosin light chain 2 polypeptide. When the 2 promoters drove the 2 reporter genes to express in the same embryos, both genes were faithfully expressed in the respective tissues, skin or muscle. When the 2 fluorescent proteins were expressed in the same skin or muscle cells under the same promoter, GFP fluorescence appeared earlier than RFP fluorescence in both skin and muscle tissues, probably owing to a higher detection sensitivity of GFP. However, RFP appeared to be more stable as its fluorescence steadily increased during development. Finally, F₁ transgenic offspring were obtained expressing GFP in skin cells under the CK promoter and RFP in muscle cells under the MLC promoter. Our study demonstrates the feasibility of monitoring expression of multiple genes in different tissues in the same transgenic organism.     

Vessel destruction by tumor-targeting Salmonella typhimurium A1-R is enhanced by high tumor vascularity

Our laboratory has previously developed a tumor-targeting double-auxotrophic mutant of Salmonella typhimurium termed A1-R. The present report demonstrates that S. typhimurium A1-R destroys tumor blood vessels and this is enhanced in tumors with high vascularity. Red fluorescent protein (RFP)-expressing Lewis lung cancer cells (LLC-RFP) were transplanted subcutaneously in the ear, back skin and footpad of nestin-driven green fluorescent protein (ND-GFP) transgenic nude mice, which selectively express GFP in nascent blood vessels. Color-coded in vivo imaging demonstrated that the LLC-RFP ear tumor had the highest cell density and the footpad tumor had the least. The ear tumor had more abundant blood vessels than that on the back or footpad. The tumor-bearing mice were treated with A1-R bacteria via tail-vein injection. Tumors in the ear were the earliest responders to bacterial therapy and hemorrhaged severely the day after A1-R administration. Tumors growing in the back were the second fastest responders to bacterial treatment and appeared necrotic 3 days after A1-R administration. Tumors growing in the footpad had the least vascularity and were the last responders to A1-R. Therefore, tumor vascularity correlated positively with tumor efficacy of A1-R. The present study suggests that bacteria efficacy on tumors involves vessel destruction which depends on the extent of vascularity of the tumor.Key words: tumor targeting bacteria, Salmonella typhimurium A1-R, Lewis lung carcinoma, RFP, GFP, nestin, nude mice     

Localization of GFP in frozen sections from unfixed mouse tissues: immobilization of a highly soluble marker protein by formaldehyde vapor.

Green fluorescent protein (GFP) and its variants, such as enhanced GFP (EGFP), have been introduced into mammalian cells by transgenes, e.g., to distinguish donor from host cells after transplantation. Free GFP is extremely soluble and leaks out from liquid-covered cryostat sections so that fixation of whole organs before sectioning has been mandatory. This precludes the analysis of serial sections with respect to fixation-sensitive enzyme activities and antigens. We describe here a vapor fixation for sections from unfixed cryostat blocks of tissue that allows unrestricted enzyme and immunohistochemistry on adjacent sections, as demonstrated for cross-striated muscle and other tissues from EGFP transgenic "green mice" and for a transplantation experiment.     

Subcellular targeting of green fluorescent protein to plastids in transgenic rice plants provides a high-level expression system

In order to develop a high-level expression system in transgenic rice, we inserted a synthetic gene (sgfp) encoding a modified form of the green fluorescent protein (GFP) into two expression vectors, Act1-sgfp for an untargeted and rbcS-Tp-sgfp for a chloroplast targeted expression. Several fertile transgenic rice plants were produced by the Agrobacterium-mediated method. Confocal microscopic analyses demonstrated that, in cells expressing the Act1-sgfp, GFP fluorescence was localized within the cytoplasm and nucleoplasm whereas, in cells expressing the rbcS-Tp-sgfp fusion gene, the fluorescence was specifically targeted to chloroplasts and non-green plastids. The levels of sgfp expression were about 0.5% of the total soluble protein in mature leaf tissues of the Act1-sgfp transformed lines. In contrast, expression levels were markedly increased in mature leaf tissues of the rbcS-Tp-sgfp transformed lines, yielding about 10% of the total soluble protein. N-terminal sequencing of the localized GFPs revealed that the Tp-GFP fusion protein was correctly processed during import to non-green plastids, as well as to chloroplasts. Thus, our results demonstrate that GFP can be produced at high levels and localized in specific subcellular spaces of transgenic plants, providing a high-level expression system for general use in rice, an agronomically important cereal.     

The green fluorescent protein as a marker to visualize plant mitochondria in vivo

To determine how to utilize the green fluorescent protein (GFP) as a marker for subcellular localization and as a label for plant mitochondria in vivo, transgenic suspension cells and tobacco plants expressing GFP with and without a mitochondrial localization signal were generated. The first GFP form used, GFP1, is easily observable in cells with low autofluorescence, such as suspension cells or trichomes, but masked in green tissue. For the visualization of GFP in cells and tissues with high autofluorescence, such as leaf, the use of a very strong promoter (35S35SAMV), a highly expressed modified mGFP4 coding region and a brighter mutant form of GFP (S65T) was necessary. Confocal or two-photon laser scanning microscopy reveal a distinct subcellular localization of the fluorescence in cells expressing GFP or coxIVGFP. In cells expressing untargeted GFP, fluorescence accumulates in the nucleoplasm but is also distributed throughout the cytoplasm. It is excluded from vacuoles, nucleoli and from round bodies that are likely to be leucoplasts. In contrast, fluorescence is localized specifically to mitochondria in cells expressing coxIVGFP fusion protein as shown by co-localization with a mitochondrial-specific dye. This permits the direct observation of mitochondria and mitochondrial movements in living plant cells and tissues throughout plant development. Three-dimensional reconstruction of individual cells can give additional information about the distribution and numbers of mitochondria.     

Parabiosis and transplantation models show no evidence of circulating dermal fibroblast progenitors in bleomycin-induced skin fibrosis

To test the hypothesis of an extra-dermal origin of dermal fibroblasts, parabiosis, and transplantation models were developed utilizing a collagen promoter green fluorescent protein (GFP) reporter transgene expressed in dermal fibroblasts. Parabiotic pairs were treated with bleomycin to induce the skin fibrosis that was evaluated for a dense deposition of collagen and inflammatory cell infiltrates in the thickened dermis in comparison with parabiotic pairs treated with saline. Although, in all cases, repeated injection of bleomycin for 4 weeks induced skin fibrosis, only a few GFP positive cells were detected in skin samples from some of the treated non-transgenic mice. Unexpectedly, similar results were observed in saline treated controls. Furthermore, bone marrow chimeras were created in which non-transgenic recipient mice received injections of bone marrow cell preparations isolated from pOBCol3.6GFP transgenic mice. After bone marrow chimerism had been successfully established, fibrotic lesions in the skin were induced by local bleomycin injections. Donor GFP expressing cells were observed in the skin from all recipient mice. However, no difference in the presence of GFP expressing cells was observed between non-treated mice or mice treated with bleomycin or saline. A large number of GFP expressing cells were observed in the lung preparations from all chimeric mice. Mac-3 antibody immunostaining confirmed a macrophage phenotype for these GFP expressing cells suggesting the expression of the pOBCol3.6GFP transgene in a non-collagen producing cell. Based on these observations, we found no evidence of circulating dermal fibroblast progenitors that participate in the development of bleomycin-induced skin fibrosis.