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Lack of cathepsin activities alter or prevent the development of lung granulomas in a mouse model of… Samokhin, Andriy O; Yves Gauthier, Jacques; Percival, M D; Brömme, Dieter Jan 20, 2011

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Lack of cathepsin activities alter or prevent thedevelopment of lung granulomas in a mousemodel of sarcoidosisSamokhin et al.Samokhin et al. Respiratory Research 2011, 12:13 (20 January 2011)RESEARCH Open AccessLack of cathepsin activities alter or prevent thedevelopment of lung granulomas in a mousemodel of sarcoidosisAndriy O Samokhin1, Jacques Yves Gauthier2, M David Percival2, Dieter Brömme1*AbstractBackground: Remodeling of lung tissues during the process of granuloma formation requires significantrestructuring of the extra-cellular matrix and cathepsins K, L and S are among the strongest extra-cellular matrixdegrading enzymes. Cathepsin K is highly expressed in various pathological granulomatous infiltrates and all threeenzymes in their active form are detected in bronchoalveolar lavage fluids from patients with sarcoidosis.Granulomatous inflammation is driven by T-cell response and cathepsins S and L are actively involved in theregulation of antigen presentation and T-cell selection. Here, we show that the disruption of the activities ofcathepsins K, L, or S affects the development of lung granulomas in a mouse model of sarcoidosis.Methods: Apolipoprotein E-deficient mice lacking cathepsin K or L were fed Paigen diet for 16 weeks and lungswere analyzed and compared with their cathepsin-expressing littermates. The role of cathepsin S in thedevelopment of granulomas was evaluated using mice treated for 8 weeks with a potent and selective cathepsin Sinhibitor.Results: When compared to wild-type litters, more cathepsin K-deficient mice had lung granulomas, butindividually affected mice developed smaller granulomas that were present in lower numbers. The absence ofcathepsin K increased the number of multinucleated giant cells and the collagen content in granulomas. CathepsinL deficiency resulted in decreased size and number of lung granulomas. Apoe-/- mice treated with a selectivecathepsin S inhibitor did not develop lung granulomas and only individual epithelioid cells were observed.Conclusions: Cathepsin K deficiency affected mostly the occurrence and composition of lung granulomas,whereas cathepsin L deficiency significantly reduced their number and cathepsin S inhibition prevented theformation of granulomas.BackgroundCathepsins K, L and S are members of the papain family ofcysteine proteases that have been recently implicated inthe development of various lung diseases [1]. It is believedthat cathepsins participate in lung tissue remodeling basedon their ability to degrade extra-cellular matrix, theirinvolvement in the regulation of immune responses andtheir potential contribution to the kallikrein-kinin system[2-5]. In this study, we investigated the roles of cathepsinsK, L, and S in the development of granulomas in mouselungs that have features of human granulomas ofsarcoidosis [6]. Sarcoidosis is a systemic disease character-ized by the presence of noncaseating epithelioid granulo-mas with a pulmonary involvement in ~90% of thepatients [7,8]. Cathepsins K, L, and S are expressed bylung macrophages, fibroblasts, and epithelial cells [9].Significant expression of cathepsin K was first found ingranulomas induced by Echinococcus granulosus inbovine lung [10]. A strong expression of cathepsin K wasalso observed in epithelioid and multinucleated giant cells(MGCs) in patients with sarcoidosis and tuberculosis[11,12]. The presence of active forms of cathepsins K, Land S was found in bronchoalveolar lavage fluids frompatients with sarcoidosis [13]. Recently, we described thatApoe-/- mice fed a cholate-containing high fat diet developlung granulomas that have many features of human* Correspondence: dbromme@interchange.ubc.ca1Department of Oral Biological and Medical Sciences, Faculty of Dentistry,University of British Columbia, Vancouver, BC, CanadaFull list of author information is available at the end of the articleSamokhin et al. Respiratory Research 2011, 12:13© 2011 Samokhin et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the CreativeCommons Attribution License (, which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.granulomas of sarcoidosis [6]. Epithelioid and MGCs insuch granulomas have shown strong immunostaining forcathepsin K suggesting that this protease might beinvolved in granuloma formation or resorption (6).Similarly to cathepsin K, cathepsins L and S are ableto degrade major extracellular proteins [14] but they arealso involved in immune responses [15,16]. Since cathe-psins L and S play significant role in antigen presenta-tion and T cell selection [15,17] and the formation ofgranulomas has been linked to T cell activation [18-21],the disruption of cathepsins L and S activities mightaffect the development of granulomas.Thus, based on the strong expression of cathepsin K ingranulomas and the pivotal role of cathepsins S and L inthe antigen presentation and T-cell selection, we hypothe-sized that the disruption of these protease activities mightinterfere with lung granuloma formation. In this study, weinvestigated the effect of cathepsin K and L deficienciesand cathepsin S inhibition on the development of lunggranulomas in Apoe-/- mice on Paigen diet.MethodsAnimalsThree groups of mice were used: apolipoprotein E-defi-cient (Apoe-/-) mice (Jackson Laboratories), doubleknockout mice lacking apolipoprotein E and cathepsinK (Apoe-/- Ctsk-/-) (n = 10) and double knockout micelacking apolipoprotein E and cathepsin L (Apoe-/-Ctsl-/-) (n = 19). Double knockout Apoe-/- Ctsk-/- andApoe-/- Ctsl-/- mice were generated by crossing Apoe-/-with the Ctsk-/- or Ctsl-/- mice as previously described[22]. Ctsk-/- and Ctsl-/- mice were kindly provided byDrs. P. Saftig (University of Kiel, Germany) and C.Peters (University of Freiburg, Germany). The singlecathepsin deficiencies have the following phenotypes:Cathepsin K-deficient mice show an osteopetrotic phe-notype with excessive trabeculation of the bone-marrowspace [23] and increased fibrosis in lungs after treatmentwith bleomycin [24]. Cathepsin L-deficient mice defi-cient mice develop periodic hair loss and epidermalhyperplasia [25].The following primer sequences were used for ApoE:5"-GCCTAGCCGAGGGAGAGCCG-3"; 5"-TGTGACTTGGGAGCTCTGCAGC-3"; 5"-GCCGCCCCGACTG-CATCT-3"; for cathepsin K: 5"-GCCACACCCACACCCTAGAAG-3"; 5"-ACA AGT GTA CAT TCC CGTACC-3"; and for cathepsin L: 5"-GGAGGGAGAGCGA-TATGGG-3"; 5"-TTCCTCATTGGTCTT-CCG-3"; 5"-CGGAGAACCTGCGTGCAATCC-3”. At 6 weeks of agemice were switched from normal to Paigen fat diet(HFD) which contained 18% fat, 1% cholesterol and 0.5%cholate; Test diet 57W4; Purina Mills. LLC, St. Louis,MO). After 16 weeks on HFD, mice were euthanizedafter overnight fasting by exsanguination under xylazine-ketamine anesthesia. Another two groups of Apoe-/-mice were studied after 8 weeks on HFD, one groupreceived high fat diet alone (n = 12) and another receivedthe same diet plus 0.01% w/w cathepsin S inhibitor (n =12). The medicated diet was formulated by mixing thechow in meal form with finely dispersed crystalline,orally-active inhibitor to obtain a uniform distribution.The cathepsin S inhibitor (cpd 6 in [26]) was dosed asthe sulfoxide prodrug (cpd 7 (Figure 1) in [26]) which israpidly converted into the active sulfone inhibitor in vivo.The mice consumed approximately 4 g food per day withno difference in food intake or body weight increase(average final body weight 23.7 g males, 20.0 g females)between the two groups. Control Apoe-/- mice used forCD4+ cell quantification in lungs were on normal diet for22 weeks. Single cathepsin K and L null mice on high fatdiet were not evaluated as previous experiments revealedthat the induction of lung granuloma formation by highfat diet was dependent on the apolipoprotein E deficiency[6]. All animal procedures were approved by the Cana-dian Council on Animal Care.Tissue preparationAfter perfusion with ice-cold phosphate-buffered saline(PBS), lungs and thymuses were fixed in 10% bufferedformalin for 5 hours at 4°C, embedded in paraffin, and5 μm sections were cut and mounted onto Superfrost/Plus slides (Fisher-Scientific, Ottawa, ON).ImmunohistochemistrySections were dewaxed, rehydrated, blocked with 10%goat serum in PBS, and incubated overnight at 4°C withthe primary antibody in 1% BSA in PBS: affinity purifiedrabbit polyclonal anti-cathepsin K (1: 50) [27], mousemonoclonal antibody against SMC a-actin (1:100, Bio-meda, Foster City, CA), rat anti-mouse Mac-3 antibody(1:100, Pharmingen, San Diego, CA), rabbit polyclonalanti-mouse osteopontin (1:100, ARP, Belmont, MA),rabbit polyclonal anti-CD4 (1:100, Abbiotec, San Diego,CA), rabbit polyclonal anti-CD8 (1:100, ANASPEC, SanJose, CA) or goat polyclonal anti-cathepsin S and anti-cathepsin L (Santa Cruz Biotechnology, Inc., Santa Cruz,CA). Sections stained for cathepsins S and L wereblocked with 10% donkey serum in PBS. As negativeFigure 1 Structure of the cathepsin S inhibitor. Nitrile-basedcathepsin S inhibitor (compound 7 according to [26]).Samokhin et al. Respiratory Research 2011, 12:13 2 of 9controls, we used mouse, rabbit, rat or goat IgG at thesame concentrations as the corresponding primary anti-bodies and for cathepsin K and L antibodies tissuesections from cathepsin K- and L-deficient mice wereused. Tissue sections were then incubated with theappropriate secondary antibody: goat anti-rabbit Cy3-conjugated, goat anti-mouse Cy2-conjugated antibody(1:200, Rockland, Gilbertsville, PA), goat anti-rat FITC-conjugated antibody (1:200, Sigma-Aldrich, St. Louis,MO), and donkey anti-goat Texas Red-conjugated(1:200 v/v, Jackson ImmunoResearch Laboratories, WestGrove, PA).Gomori’s trichrome stainingSections were deparaffinized, hydrated with a gradedalcohol series and distilled water, and placed in pre-heated Bouin’s solution at 58°C for 10 min. Sectionswere stained in Weigert’s iron hematoxylin solution for5 min, washed under running water for 30 sec, stainedwith Gomori’s trichrome solution (Sigma-Aldrich, St.Louis, MO) for 15 min, placed in 0.5% acetic acid for10 sec, and then mounted for light microscopy.Morphometry, collagen content, and cell composition ofgranulomasThe areas of granulomas stained positively for Mac-3,osteopontin, CD4 and CD8, and collagen were quanti-fied using color threshold and calculated as percentageof granuloma area. The size of granulomas was mea-sured in mm2. Trichrome stained sections were used forthe measurement of granuloma size and for the quantifi-cation of collagen content. Images were captured with aLeica DMI 6000B microscope (Leica Microsystems, Inc,Richmond Hill, ON) and analyzed with Openlab 3software.Quantification of the number of granulomas,multinucleated giant cells and CD4-positive cellsFive sections 200 μm apart from each other were ana-lyzed for each lung. For CD4-positive cell quantificationthree pictures per lung section were taken using a 40-fold magnification, avoiding areas with dominating tra-cheal or bronchial tissue. The average number of granu-lomas and multinucleated giant cells per section and theaverage number of CD4-positive cells per captured areafor each mouse were used for statistical analyses.Statistical analysisStudent’s t-tests were performed when values past testfor normal distribution. Data are presented as mean ±standard deviation. Discontinuous data (such as thenumber of granulomas) were analyzed using the Mann-Whitney U-test. Significance was concluded whenP < 0.05.ResultsCathepsins K, L and S are expressed in mouse lunggranulomasRecently, we described that Apoe-/- mice receiving HFDdevelop epithelioid lung granulomas with characteristicfeatures of granulomas of sarcoidosis [6]. Granulomaswere composed of epithelioid cells, macrophages and Tcells, and some granulomas also contained fibroblastsand multinucleated giant cells (MGCs) [6]. Figure 2Adisplays the typical phenotype of granulomas seen inthis model. Similarly to granulomas of sarcoidosis,mouse lung granulomas were intensively stained forcathepsin K with the highest immunoreactivity inepithelioid cells forming the core of the granulomas(Figure 2B). Analysis of consecutive sections stained forcathepsins L and S revealed that similarly to cathepsinK, cathepsin L was prevalently observed in the core ofgranulomas, whereas cathepsin S staining was weakerand uniformly distributed throughout the lung tissue(Figure 2C, D).Cathepsin K deficiency increased the incidence ofgranulomatous infiltrations in lungsSimilarly to Apoe-/- mice, Apoe-/- Ctsk-/- mice receivingHFD showed fibrotic changes in lung tissues and thepresence of such inclusions as Schaumann’s bodies andcrystalline structures (Figure 3A), which are nonspecificbut are often present in patients with sarcoidosis.Apoe-/- Ctsk-/- mice also developed inducible bronchus-associated lymphoid tissues (iBALT) which are usuallyinduced by inflammatory reactions and are present inFigure 2 Expression of cathepsins in lung granulomas .Cathepsins K, L and S are expressed in lung granulomas of Apoe-/-mice. (A), trichrome stained section shows well-formed lunggranulomas. (B), cathepsin K immunostaining (red - cathepsin K,blue - nuclei). (C), cathepsin L immunostaining (red - cathepsin L,blue - nuclei). (D), cathepsin S immunostaining (red - cathepsin S,blue - nuclei). (A), scale bar 130 μm, (B-D), scale bars 65 μm.Samokhin et al. Respiratory Research 2011, 12:13 3 of 9bronchovascular bundles [28] (Figure 3B). Evidences ofacute lung injury, such as alveolar monocyte/neutrophilinfiltration and proteinosis, were also observed (Figure3B and 3C). In Apoe-/- mice, 41% of the animals dis-played lung granulomas, whereas in their cathepsinK-deficient littermates this number reached 88%(table 1). Notable differences in the morphology of gran-ulomatous infiltrations were also observed. In some lungareas, the presence of epithelioid cells did not result inthe development of well-formed and ball-shaped granu-lomas that were predominant in cathepsin K-expressingmice. In cathepsin K-knockout mice, epithelioid cellswere often organized in amorphous or ring-like struc-tures formed by epithelioid cells (Figure 3D) and granu-lomas often contained an accumulation of fibroblast-likeshaped cells showing positive staining for a-actin (Fig-ure 3E). In some lung areas, extensive accumulation ofcollagen fibers and epithelioid cells covered large areasbetween airways and blood vessels (Figure 3F, G). Inmore fibrotic areas that had honeycombing appearance,individual epithelioid cells were randomly dispersed (Fig-ure 3H). The average size of granulomas was significantlysmaller in cathepsin K-deficient mice (see below) whencompared to cathepsin K-expressing littermates, butsome granulomas reached comparatively large sizes (Fig-ure 2I) that might be related to changes in granulomadevelopment in the absence of cathepsin K.Analysis of lung granuloma composition revealed thatcathepsin K-deficient mice contained significantly highernumber of MGCs per lung section (Figure 4A-C). Granu-lomas contained foreign body-type MGCs, with randomdistribution of nuclei (Figure 4A) and Langhans-typeMGCs with horseshoe-like arrangements of nuclei(Figure 4B). Epithelioid cells and MGCs were intensivelyFigure 3 Structural changes in lungs of Apoe-/-Ctsk-/- mice. (A), extensive fibrosis with Schaumann’s bodies (arrowhead) and crystallinestructures (arrow). (B), inducible bronchus-associated lymphoid tissues (iBALT) and alveolar monocyte/neutrophilic infiltration. (C), proteinosis. (D),ring-like structures formed by epithelioid cells. (E), smooth muscle cell a-actin positive cells in granulomas (green - smooth muscle cell a-actin,blue - nuclei). (F), accumulation of epithelioid cells between layers of collagen fibers (* shows area magnified on G). (H), individual epithelioidcells in fibrotic areas with honeycombing appearance. (I), two granulomas with relatively large size. (A-D, F-I), trichrome stained sections. (A-E andI), scale bars 65 μm; (F), scale bar 260 μm; (G), scale bar 30 μm; (H), scale bar 130 μm.Table 1 Percentage of mice with granulomas, proteinosisor iBALT in lungsApoe-/-(16 w)Apoe-/-Ctsk-/-(16 w)Apoe-/-Ctsl-/-(16 w)Apoe-/-(8 w)Apoe-/-(cat S inh)(8 w)Granulomas 41 88 31 41 -Proteinosis 17 11 26 9 8iBALT 47 77 31 36 15Samokhin et al. Respiratory Research 2011, 12:13 4 of 9stained for osteopontin, whereas the macrophage markerMac-3, was not expressed in giant cells (Figure 4D-F).Granuloma cell composition analyzed by immunohisto-chemical staining did not reveal significant differences inthe amount of CD4+ and CD8+ T cells as well as Mac-3(macrophage marker) and osteopontin positive cells(epithelioid cells marker) in Apoe-/- Ctsk-/- mice whencompared to their cathepsin K-expressing littermates(Figure 4G and [6]). The collagen content was signifi-cantly higher in granulomas of mice lacking cathepsin K(Figure 4H).Cathepsins K and L deficiencies and cathepsin Sinhibition decreases the number and size of lunggranulomasApoe-/- mice lacking cathepsin K have shown a higherincidence of lung granulomas compared to Apoe-/- mice(table 1), but the size of granulomas was significantlysmaller (Figure 5A, B, D). Cathepsin L deficiencyresulted in the lower incidence and smaller size ofgranulomas (table 1 and Figure 5C, D). The number ofgranulomas decreased dramatically from an average of34 per lung section in Apoe-/- mice to one in Apoe-/-Ctsl-/- mice (Figure 5E). After 8 weeks of HFD the sizeof granulomas in Apoe-/- mice was smaller compared to16 weeks of diet (12.6 ± 3.66 mm2 vs. 20.8 ± 4.3) butgranulomas were still well-formed (Figure 5F) and simi-larly to 16 weeks, they were present in 41% of mice(table 1). In cathepsin S inhibitor-treated mice only indi-vidual epithelioid cells without well-formed granulomaswere observed (Figure 5G) and epithelioid cells werepresent in 30% of mouse lungs. After one week of dos-ing, morning blood levels of active inhibitor reached1.0 ± 0.16 μM (n = 6 animals). This concentration likelyapproximates the peak blood level as mice feed predo-minantly at night. Cathepsin S is highly expressed in thespleen and antigen-presenting cells and its inhibitionimpairs antigen presentation and causes a build-up ofintermediate invariant chain (Ii) breakdown products[29,30]. Previously, we reported significant accumulationFigure 4 Granuloma composition in cathepsin K-deficient mice. (A), granuloma with several foreign body-type MGCs. (B), granuloma withLanghans-type MGC (C), cathepsin K-deficient mice had significantly higher number of MGCs per lung section, (* - p < 0.05 when compared toApoe-/- mice). (D), Mac-3 positive cells in granuloma (green - Mac-3, blue - nuclei), (E), osteopontin-containing epitheloid and giant cells (red -osteopontin, blue - nuclei), (F), merge of D and E. (G), percentage of granuloma area stained for Mac-3, osteopontin, CD4 and CD8. (H) Thecollagen-stained area was quantified using color threshold and calculated as percentage of granuloma area (* - p < 0.05 when compared toApoe-/- mice). (A, D-F), scale bars 30 μm, (B), scale bar, 20 μm.Samokhin et al. Respiratory Research 2011, 12:13 5 of 9of 10 kDa products of Ii degradation in cathepsin S inhi-bitor-treated mice after 8 weeks of HFD that providesan evidence of an efficient inhibition of cathepsin S [31].Effect of cathepsins on thymus hypertrophyIn addition to fibrosis and granulomatous inflammationin lung, HFD induces fibrotic changes and hypertrophyin the thymus. Previously, we observed that after16 weeks on HFD, Apoe-/- mice had more than a 3-foldincrease in thymus weight compared to their littermateson normal diet [6]. Cathepsin K and L deficiencies andcathepsin S inhibition did not prevent the developmentof fibrotic changes in thymi. In all mice, an accumula-tion of collagen fibers and the presence of MGCs wereobserved (Figure 6A-C). But the thymus hypertrophywas dependent on cathepsin activities: mice receivingthe cathepsin S inhibitor, or lacking cathepsin K, haveshown insignificantly lower weights of thymi, whereas inApoe-/- Ctsl-/- mice thymi had more than 5 times smal-ler weights when compared to Apoe-/- mice (Figure 6D,F). As cathepsin L-deficient mice had a lower total bodyweight, a ratio between thymus and total body weightwas evaluated. This proportion was significantly lowerin cathepsin K-null mice and more than 4-times smallerin cathepsin L-deficient mice (Figure 6E).Accumulation of CD4-positive cells in lungs is affected bycathepsin S inhibitor and cathepsin L deficiencyThe formation of lung granulomas was accompanied bya more than 5-fold increase in the number of CD4-positive cells in lungs of mice on HFD when comparedto mice on normal diet (Figure 7A, B). Cathepsin K defi-ciency did not affect the CD4 population when com-pared to Apoe-/- mice. In contrast, disruption ofcathepsin L and S activities resulted in an 18% and 43%lower accumulation of CD4-positive cells in lungs(Figure 7B, C).DiscussionThe formation of lung granulomas results in an exten-sive extracellular matrix remodeling. Collagen and elas-tin are the major components of the pulmonary matrixFigure 5 Changes in granuloma size and numbers. Granulomas in Apoe-/- (A), Apoe-/-Ctsk-/- (B) and Apoe-/-Ctsl-/- mice after 16 weeks on HFD (C).(D), size of granulomas was significantly smaller in cathepsin K- and L-deficient mice. (E), number of granulomas in cathepsin L-deficient mice wasdramatically decreased. (F), granulomas in Apoe-/- mice after 8 weeks on HFD. (G), Apoe-/- mice treated with cathepsin S inhibitor developed onlyindividual epithelioid cells after 8 weeks on HFD. (A-C, F, G), trichrome stained sections, scale bars 65 μm. * - p < 0.05 when compared to Apoe-/- mice.Samokhin et al. Respiratory Research 2011, 12:13 6 of 9and it is believed that a cooperative action of multipleenzymes is required for its turnover. Cathepsin K has aunique ability to cleave highly efficiently triple helicalcollagen at multiple sites and to act as a potent elastaseas well [32]. Its strong expression in lung granulomassuggested an important role in granuloma formationand resolution, and indeed, lungs of Apoe-/- Ctsk-/-mice showed significant differences in granulomaappearance, size, and composition. The increased inci-dence of lung granulomas in cathepsin K-deficient mice(88% vs. 41%) correlates with the increased collagenfibers deposition (10% vs 20%) that may consequentlyresult in a delayed granuloma resolution. Lung granu-loma formation and their spontaneous resolution ascommonly observed in patients with sarcoidosis [33]require remodeling of the extracellular matrix. It istempting to speculate that the increased amount of col-lagen in granulomas (Figure 4H) and the presence ofabundant collagen fibers between epithelioid cells inareas without well-formed granulomas (Figure 3F, G) inCtsk-/- mice is due to the lack of the collagenase activityof cathepsin K. This accumulation of collagen fibersmight also be responsible for the smaller number andsize of granulomas. In our measurements, accumulationsof epithelioid cells were considered as granulomas onlywhen they were present as well-formed and ball-shapedstructures that are characteristic for sarcoidosis. InApoe-/- Ctsk-/- mice, epithelioid cells were oftenFigure 6 Fibrosis and MGCs in thymus. (A), fibrotic thymus in Apoe-/-Ctsl-/- mice. (B), foreign body type MGCs with random distribution ofnuclei in Apoe-/-Ctsk-/- mice. (C), Langhans-type MGCs with horseshoe-like arrangement of nuclei in cathepsin S inhibitor treated mice. (D),cathepsin L deficiency prevents hypertrophy of thymus. (E), proportion of thymus to total body weight was significantly lower in cathepsin K-and L-deficient mice. (F), cathepsin S inhibitor treatment did not prevent thymus hypertrophy. * - p < 0.05 when compared to Apoe-/- mice. A-C,trichrome staining. (A), scale bar 130 μm, (B, C), scale bars 30 μm.Figure 7 Effect of cathepsins on the amount of CD4-positive cells in lungs. The number of CD4-positive cells (A) was more than a 5-timeshigher in lungs of Apoe-/- mice as a result of HFD-feeding (B). Apoe-/- Ctsk-/- mice did not reveal a significant difference in its CD4 population,whereas Apoe-/- Ctsl-/- mice showed less dramatic accumulation of CD4+ cells when compared to Apoe-/- mice (* - p < 0.05 between Apoe-/-mice on HFD and Apoe-/- mice on normal diet; * - p < 0.05 when compared to Apoe-/- mice on HFD). Cathepsin S inhibitor treatment resultedin a significant reduction of CD4+ cells in lungs of mice on HFD (C, * - p < 0.05 when compared to mice on HFD without inhibitor). (A), Scalebar 30 μm.Samokhin et al. Respiratory Research 2011, 12:13 7 of 9observed forming ring-like structures with dispersed col-lagen fibers, or were randomly distributed in fibroticareas (Figure 3D, H).The cell composition of granulomas in cathepsinK-deficient mice was also changed. They contained asignificantly higher number of MGCs. This type of cellsis formed by the fusion of cells from the monocyte-macrophage lineage [34]. In atherosclerotic plaquesfrom Apoe-/- Ctsk-/- mice, macrophages have anincreased size [35] and microarray analyses haverevealed the upregulation of several macrophage genes,including CD36 [36]. Since CD36 participates in macro-phage fusion [37], we suggest that it might be responsi-ble for the increased number of MGCs in cathepsinK-deficient mice. The disruption of cathepsins L and Sactivities resulted in a more significant effect on granu-loma formation. Cathepsin L deficiency reduced the sizeand the number of lung granulomas whereas mice trea-ted with the cathepsin S inhibitor did not develop well-formed granulomas.Analysis of available literature data suggests that thepreventive effect of cathepsin L deficiency or cathepsinS inhibition on lung granuloma development may notonly depend on their extracellular matrix-degradingactivities, but on their involvement in antigen presenta-tion as well [17,38]. Cathepsin S is expressed in B cells,macrophages, and dendritic cells and is required forinvariant chain (li) degradation and antigen processing[30]. Cathepsin S-deficient mice have decreased MHCclass II presentation in B and dendritic cells, and areduced number of CD4+ T-cells [15]. On the otherhand, cathepsin L is expressed in cortical thymic epithe-lial cells and macrophages and is responsible for lidegradation in CD4+ T cell selection in the thymus [17].Cathepsin L-deficient mice have a reduction in theirnumbers of CD4+ cells in thymus and peripheral organs[39]. The roles of cathepsins S and L on the functionsof CD4+ may have a direct influence on sarcoidosisdevelopment. T cell activation is mandatory for thedevelopment of granulomatous reactions and CD4+ Tcells of the Th1-type are essential for the formation andthe maintenance of granulomas [18-21]. The decreasedamount of CD4+ cells in lungs of mice lacking cathepsinL or treated with cathepsin S inhibitor (Figure 7B, C)supports the suggestion that the effect of these twocathepsins on the granuloma formation is related totheir role in antigen presentation and T-cell selection.In addition to its involvement in antigen presentation,cathepsin L has been described to play a role in T-cellactin polymerization, shape polarization, chemotaxis.Cathepsin L deficiency significantly decreases theexpression of laminin, fibronectin, and collagens I and IIin thymus of cathepsin L-deficient mice [40]. This mightpartially explain why Apoe-/- Ctsl-/- mice hadsignificantly smaller thymi compared to Apoe-/- mice(Figure 7D, E).In conclusion, our results show that the disruption ofcathepsin L and S activities prevents the development oflung granulomas, whereas cathepsin K deficiency resultsin altered granuloma composition in mice. These resultssuggest that interventions in cathepsin S and L activitiesmay yield a therapeutic benefit for patients with sarcoi-dosis, i.e., a potential prevention of disease progression.Such an approach, however, would require extreme cau-tion as both cathepsins have been described as criticalparticipants in antigen presentation and their inhibitionmay result in increased infection and cancer rates.AcknowledgementsThe authors gratefully acknowledge Drs. Paul Saftig (University of Kiel,Germany) and Christoph Peters (University of Freiburg, Germany) forproviding the mouse strains for cathepsin K and L-deficiencies. We alsogratefully acknowledge Stephanie Alleyn, Aleksandar Popovic, Simon Wong,Denis Normandin and Réné St-Jacques from Merck-Frosst for their excellenttechnical assistance and assistance with animal care during this study. Thiswork was supported by the CIHR grant C04-0435 and a Canada ResearchChair Award (D. B.).Statement of Authors’ contributionsAOS designed and carried out experiments, analysed data and wrote thepaper, JYG carried out experiments with cathepsin S inhibitor, MDPdesigned and carried out experiments with cathepsin S inhibitor and wroteinhibitor-related sections of the paper, DB conceived experiments, analyseddata and wrote the paper. All authors have approved the final manuscript.Declaration of competing interestsThe authors declare that they have no competing interests.Author details1Department of Oral Biological and Medical Sciences, Faculty of Dentistry,University of British Columbia, Vancouver, BC, Canada. 2Merck Frosst Centerfor Therapeutic Research, Kirkland, QC, Canada.Received: 9 September 2010 Accepted: 20 January 2011Published: 20 January 2011References1. Wolters PJ, Chapman HA: Importance of lysosomal cysteine proteases inlung disease. Respir Res 2000, 1(3):170-177.2. 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Honey K, Nakagawa T, Peters C, Rudensky A: Cathepsin L regulates CD4+T cell selection independently of its effect on invariant chain: a role inthe generation of positively selecting peptide ligands. J Exp Med 2002,195(10):1349-1358.40. Lombardi G, Burzyn D, Mundinano J, Berguer P, Bekinschtein P, Costa H,Castillo LF, Goldman A, Meiss R, Piazzon I, et al: Cathepsin-L influences theexpression of extracellular matrix in lymphoid organs and plays a role inthe regulation of thymic output and of peripheral T cell number.J Immunol 2005, 174(11):7022-7032.doi:10.1186/1465-9921-12-13Cite this article as: Samokhin et al.: Lack of cathepsin activities alter orprevent the development of lung granulomas in a mouse model ofsarcoidosis. 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