Bone marrow stem cells expressing keratinocyte growth factor via an inducible lentivirus protects against bleomycin-induced pulmonary fibrosis

Abstract

Many common diseases of the gas exchange surface of the lung have no specific treatment but cause serious morbidity and mortality. Idiopathic Pulmonary Fibrosis (IPF) is characterized by alveolar epithelial cell injury, interstitial inflammation, fibroblast proliferation and collagen accumulation within the lung parenchyma. Keratinocyte Growth Factor (KGF, also known as FGF-7) is a critical mediator of pulmonary epithelial repair through stimulation of epithelial cell proliferation. During repair, the lung not only uses resident cells after injury but also recruits circulating bone marrow-derived cells (BMDC). Several groups have used Mesenchymal Stromal Cells (MSCs) as therapeutic vectors, but little is known about the potential of Hematopoietic Stem cells (HSCs). Using an inducible lentiviral vector (Tet-On) expressing KGF, we were able to efficiently transduce both MSCs and HSCs, and demonstrated that KGF expression is induced in a regulated manner both in vitro and in vivo. We used the in vivo bleomycin-induced lung fibrosis model to assess the potential therapeutic effect of MSCs and HSCs. While both populations reduced the collagen accumulation associated with bleomycin-induced lung fibrosis, only transplantation of transduced HSCs greatly attenuated the histological damage. Using double immunohistochemistry, we show that the reduced lung damage likely occurs through endogenous type II pneumocyte proliferation induced by KGF. Taken together, our data indicates that bone marrow transplantation of lentivirus-transduced HSCs can attenuate lung damage, and shows for the first time the potential of using an inducible Tet-On system for cell based gene therapy in the lung.

Figure 1. In vitro characterization of MSCs expressing KGF and their therapeutic potential in bleomycin-induced lung injury.

A) Schematic representation of the lentiviral vector used in this study. B) Schematic of experimental design. C57Bl/6 mice received bleomycin (BLM) by o.p. instillation, followed 8 h later by i.v. injection of 0.5×10⁶ MSCs-eGFP or MSCs-KGF-eGFP, repeated three days later and then sacrificed at day 14. C) eGFP expression of transduced MSCs at the day of injection. D) Rare MSCs-eGFP and MSC-KGF-eGFP cells are detected in the lung after injury by immunohistochemistry (brown stained cells, arrows). (Scale bar = 100 µm. Inserts, scale bar = 50 µm). E) Representative images of Martius Scarlet Blue stained lung sections. (Scale bar = 100 µm). F) Comparison of morphometric analysis using Ashcroft Score, 14 days after bleomycin, showed no reduction of fibrosis with transduced MSCs. Bars represent means ± SEM. G) RT-PCR analysis for Collagen 1α1 mRNA from lung extracts showed significant differences between bleomycin and bleomycin +MSCs-KGF-eGFP groups while H) there was no difference in lung collagen accumulation as measured by reverse-phase HPLC quantification of lung hydroxyproline. Statistical differences were detected between saline and bleomycin groups regardless of MSC administration (*p<0.05). Bars represent means ± SEM. Statistically significant differences are indicated by p-values from a One-Way ANOVA test.

Figure 2. Lineage negative HSCs KGF-eGFP transduction and differentiation potential.

A) Schematic of experimental design. 8 weeks-old C57Bl/6 mice were lethally irradiated followed by intravenous injection of 0.6×10⁶ transduced lin- HSCs (BMT). 7 weeks after BMT, mice received doxycycline in drinking water to induce gene expression and chimerism was analysed one week later. 9 weeks after BMT, mice received bleomycin by o.p. instillation and were sacrificed at day 14. B) Flow cytometry analysis showed eGFP expression in vitro after adding doxycycline to lin- HSCs transduced with LV-eGFP (MOCK) and LV-KGF-eGFP. C) Amount and type of colonies in methylcellulose after culture of transduced Lin^- HSCs with MOCK or KGF-eGFP was unchanged. BFU-E, erytrocyte; CFU-G, granulocyte; CFU-M, myeloid; CFU-GM, mixed granulocyte and myeloid.

Figure 3. Therapeutic potential of KGF expressing Lin- HSCs in bleomycin-induced lung fibrosis in mice.

A) GFP immuno-staining 14 days after bleomycin demonstrated brown stained cells (arrows) in mice given doxycycline in drinking water. (Scale bars = 100 µm; inserts, scale bars = 50 µm). B) Martius Scarlet Blue stained lung sections showed a reduction of fibrosis in mice expressing KGF-eGFP. Scale bar = 100 µm. C) Semi-quantitative representative morphometric analysis using Ashcroft Score, confirmed the reduction in lung fibrosis when KGF is expressed by bone marrow cells. (p = 0.03; Mann-Whitney). D) RT-PCR analysis for Collagen 1α1 mRNA from lung extracts showed reduced collagen in the bleomycin + KGF-eGFP group versus bleomycin only group (p = 0.012; One-Way ANOVA). E) KGF attenuated lung collagen accumulation after bleomycin instillation in mice, as measured by reverse-phase HPLC quantification. A statistical significant increase was detected in saline versus bleomycin only group, but not the HSC-KGF treated group. (p = 0.0179, One-Way ANOVA). All bars represent means ± SEM.

Figure 4. Bone marrow derived cells expressing KGF induced alveolar epithelial cell proliferation within the injured lung.

A) Double immunofluorescence with lung epithelial type II marker Surfactant Protein C (SP-C) (green) and proliferation marker Ki-67 (red) on paraffin lung sections, 14 days after bleomycin administration. Bone marrow cells expressing KGF increased proliferation of alveolar type II cells in both saline and BLM groups. Arrows indicate proliferating lung epithelial cells. (Scale bars = 100 µm; inserts, scale bars = 50 µm). B) Contiguous light microscopy photomicrographs corresponding to A. C) Quantification of double positive SP-C and Ki-67 stained cells showed an increase in proliferating epithelial cells when KGF is expressed. Bars represent mean from 6-areas/lung sections counted ± SEM. (P-values from Two-Way ANOVA). D) qRT-PCR analysis for KGF mRNA from lung extracts showing increased levels of KGF in doxycycline treated mice. Bars represent means ± SEM. (P-values from Student's T-test).

Figure 5. Bone marrow derived cells expressing KGF reduce inflammatory cytokines, macrophage chemo-attractants and α-sma.

A) qRT-PCR analysis for inflammatory cytokines revealed significant reductions of TNF-α and CCL-2 and CCL-9 chemokine mRNA in lung extracts from doxycycline treated BLM-KGF mice compared with BLM treatment alone. Bars represent means ± SEM. (P-values from One-Way ANOVA). B) α-sma stained lung sections showed a reduction of myofibroblast-type cells in the lungs of mice treated with KGF-eGFP. Scale bar = 50 µm.