Allergic rhinitis (AR) is a non-infectious chronic inflammatory disease of the nasal mucosa, which is mainly mediated by IgE after the body is exposed to allergens. It has been shown that transplantation of human mesenchymal stem cells (MSCs) into AR animal models can improve the AR behavioral phenotype. Furthermore, there are recent studies that states exosomes are the main mediators of MSC therapy. However, the effect of exosomes on AR has not been investigated.
In the established AR mouse model, different concentrations of MSC-derived exosomes (MSCs-Exo) were applied via intranasal delivery. The AR symptom scores, the eosinophils in the nasal mucosal section, the inflammation infiltration in the spleen section, and IgE, ovalbumin-specific IgE (OVA-sIgE), histamine, IgG1, IgG2a and other Th1/Th2 related inflammatory factors were evaluated by Hematoxylin–eosin staining, Elisa, real-time PCR.
We found that intranasal administration of MSCs-Exo could not only reduce the behavior of nasal scratching and sneezing in mice, but also cause a decline in related immune indicators via the MAPK pathway, including the spleen index, tissue staining, and the expression of inflammation-related cytokines. Moreover, we found that the optimal concentration of MSCs-Exo was 4×108/mL.
The significant beneficial effects of exosomes may be exploited to develop a new, non-invasive treatment strategy for AR.
Allergic rhinitis (AR) is a non-infectious inflammatory disease of the nasal mucosa which is mainly mediated by IgE and driven by Th2 cells after exposure to allergens. The main clinical symptoms are sneezing, a runny nose, nasal itching, and nasal congestion1. It has been reported that 10–40% of adults worldwide suffer from AR, and in developing countries, the situation is even worse, as the number of cases of AR rapidly increased in recent decades, especially in China2. The main treatment methods for AR are allergen avoidance, drug therapy, and specific immunotherapy3. However, drug therapy can only manage symptoms and cannot reverse or alleviate the immune imbalance. Although specific immunotherapy can desensitize patients to allergens and prevent the development of lesions, it has a long treatment cycle, which tends to result in poor patient compliance and unproductive treatments4. Therefore, it is urgent to find new directions for effective treatment.
Mesenchymal stem cells (MSCs) have the potential for self-renewal and multi-directional differentiation5 and have immunomodulatory functions6. Previous studies have shown that transplantation of MSCs via the tail vein into an AR mouse model can improve symptoms7, 8. Xenogeneic MSCs have also been proven to exert similar therapeutic effects in AR mice9. In addition, MSCs can also reduce the immunological indicators and adjust the Th1/Th2 reaction balance in AR patients10. The application of MSCs has resulted in definite curative effects. However, MSCs have several disadvantages, including vascular obstruction caused by the large cells11, unpredictable differentiation in the host12, and reported concerns regarding the cancer progression13, 14.
It has also been proven that exosomes secreted by MSCs (MSCs-Exo) have the same efficacy as MSCs; more importantly, transplantation with its associated risks can be avoided15. Exosomes are homogenous vesicles with a diameter of 30–150 nm secreted by a variety of cells16. The vesicles contain different types of proteins, nucleotides, and other substances. Cells can swallow the vesicles through endocytosis so that the active substances in the vesicles can function inside the cells17. MSCs-Exo can mimic the functions of MSCs and exert similar immunomodulatory effects18. Moreover, exosomes do not have a nuclear structure and cannot be amplified in the host, and thus they are safer in clinical application19. However, the clinical use of MSCs-Exo to treat AR has never been investigated. In this paper, we show that AR mice treated with MSCs-Exo by intranasal administration showed a significant improvement in behavior and histology via MAPK signaling.
Female BLAB/c mice were purchased from Nanjing Medical University and were bred in Nanjing Drum Tower Hospital. All mice were nurtured in ventilated cages and had free access to water and food. The protocols were approved by the Animal Care and Use Committee of Nanjing Medical University and animals were treated following the National Institutes of Health Guide for the Care and Use of Laboratory Animals. All operations were carried out in accordance with the approved procedures.
AR model and MSCs-Exo treatment
BALB/c mice were sensitized with ovalbumin (OVA) (Sigma-Aldrich, A5503) and aluminum hydroxide gel (Thermo Scientific, 77161) to establish the AR model. At 4 weeks of age, the mice were randomly divided into the control group, the AR group, and the MSCs-Exo treatment group. AR mice were given an intraperitoneal injection of 100 μg OVA in 100 μl PBS combined with 100 μl aluminum hydroxide gel on days 1, 5, and 10 and were treated intranasally with 20 μl 10% OVA in PBS per nostril every day from day 15 to 21. Mice in the control group were given an intraperitoneal injection of 100 μl PBS combined with 100 μl aluminum hydroxide gel, and they were treated intranasally with 20 μl PBS per nostril every day. Mice in the MSCs-Exo treatment group were given an intraperitoneal injection of 20 μg of OVA in 100 μl PBS combined with 100 μl aluminum hydroxide gel on days 1, 5, and 10; were treated intranasally with 20 μl 10% OVA in PBS per nostril every day from day 15 to 21; and were treated intranasally with 20 μl MSCs-Exo at different concentrations per nostril every day. Administration was performed using a 10-μL pipette with no anesthetics.
After the last intranasal administration of 10% OVA on day 21, mice were separately placed in a 10×10×15 cm3 cage. After waiting for 10 min, their symptoms were observed for 10 min. The behaviors that were observed and quantified included nose scratching and sneezing.
Determination of spleen index
The spleen index was calculated according to the following formula: spleen index (mg/g) = spleen weight (mg) ÷ animal body weight (g).
Nasal lavage fluids and serum collection
At 24 h after the last intranasal administration, mice were sacrificed by cervical dislocation. PBS (1 ml) was injected into the posterior nostril and a 1.5-mL EP tube was used to collect the nasal lavage fluid at the anterior nostril. The nasal lavage fluid was centrifuged at 2000 rpm for 7 min at 4°C and stored at −20°C until analysis. Blood samples were collected from the orbital venous plexus by capillaries. The blood samples were rested for 60 min, centrifuged at 4000 rpm for 10 min at 4°C, and stored at −20°C until analysis.
Isolation of exosomes
The human umbilical cord was taken from a full-term infant, cut into small pieces, and cultured. Cells were split when the cells reached 80–90% confluence. In the following procedures, only P5 generation cells were used. After the cells grew to 70% confluence, the culture medium was discarded, the cells were washed thoroughly with PBS, and the medium was replaced with serum-free medium for 48 h. Next, the conditioned medium was collected, centrifuged at 1000 ×g for 20 min to remove cell debris, and centrifuged at 2000 ×g for 20 min, and the supernatant was filtered using a 220-nm filter. Next, the filtered supernatant was centrifuged at 10,000 ×g for 60 min at 4°C, and the supernatant was filtered using a 220-nm filter again. The filtered supernatant was centrifuged at 100,000 ×g for 3 h at 4°C, the supernatant was discarded, the pelleted exosomes were diluted in 1 ml of pulse medium, and the effective diameter of exosomes was assessed by dynamic light scattering (DLS, Brookhaven Instruments).
Transmission electron microscopy
For transmission electron microscopy (TEM), exosomes were isolated as described and directly fixed in 200 μl of 2% paraformaldehyde. Exosome preparations (20 μl) were allowed to adsorb in a 75 mesh Formvar/carbon coated grid for 30 min at room temperature. Grids were then washed with PBS (membrane side facing down) and dried using a filter paper. TEM was performed using a Hitachi H-9000 transmission electron microscope at 300 kV, and images were captured using a slow-scan CCD camera.
RNA extraction and real-time PCR
The spleen was taken from the sacrificed mice for RNA extraction using TRIzol™ Reagent (ThermoFisher, 15596026). RNA was reverse transcribed into cDNA using the RevertAid First Strand cDNA Synthesis Kit (Thermo Fisher Scientific, K1622). The concentration and integrity of RNA and cDNA were measured using a NanoDrop (Thermo Fisher, 2000). The mRNA expression values of the genes were normalized to the mRNA expression of actin. The results were calculated using the comparative cycle threshold (ΔΔCt) method. The primers used were as follows: IL-4(F): GGTCTCAACCCCCAGCTAGT; IL-4(R): GCCGATGATCTCTCTCAAGTGAT; IL-5(F): CTCTGTTGACAAGCAATGAGACG; IL-5(R): TCTTCAGTATGTCTAGCCCCTG; IL-6(F): TAGTCCTTCCTACCCCAATTTCC; IL-6(R): TTGGTCCTTAGCCACTCCTTC; IL-10(F): GCTCTTACTGACTGGCATGAG; IL-10(R): CGCAGCTCTAGGAGCATGTG; IL-13(F): CCTGGCTCTTGCTTGCCTT; IL-13(R): GGTCTTGTGTGATGTTGCTCA; IL-17(F): TTTAACTCCCTTGGCGCAAAA; IL-17(R): CTTTCCCTCCGCATTGACAC; ICAM-1(F): GTGATGCTCAGGTATCCATCCA; ICAM-1(R): CACAGTTCTCAAAGCACAGCG; IFN-γ(F): ATGAACGCTACACACTGCATC; IFN-γ(R): CCATCCTTTTGCCAGTTCCTC; CCL-11(F): GAATCACCAACAACAGATGCAC; CCL-11(R): ATCCTGGACCCACTTCTTCTT; TGF-β1(F): TCTGCATTGCACTTATGCTGA; TGF-β1(R): AAAGGGCGATCTAGTGATGGA; TGF-β2(F): CCGCTGCATATCGTCCTGTG; TGF-β1(R): AGTGGATGGATGGTCCTATTACA; IKK(F): ACAGCCAGGAGATGGTACG; IKK(R): CAGGGTGACTGAGTCGAGAC; IKB(F): GCGGATGCCGATGAATGGT; IKB(R): TGACGTAGCCAAAGACTAAGGG; JUN(F): CCTTCTACGACGATGCCCTC; JUN(R): GGTTCAAGGTCATGCTCTGTTT; JNK(F): CAGACTGTACCCTCAAGATCCT; JNK(R): ATGCACCCGACAGACCAGA; ERK(F): GGTTGTTCCCAAATGCTGACT; ERK(R): CAACTTCAATCCTCTTGTGAGGG; FOS(F): CGGGTTTCAACGCCGACTA; FOS(R): TTGGCACTAGAGACGGACAGA.
Standard wells and blank wells were set in accordance with the protocol of the Bioswamp ELISA kit. Serum (40 μl) was added to each sample well, and 10 μl biotinylated antibody and 50 μl HRP-conjugated reagent were added to each well except the blank well. After incubating for 30 min at 37°C, washing buffer was added to every well and samples were rested for 30 s five times. Then, chromogen solution was added to each well and samples were incubated for 10 min at 37°C. Lastly, stop solution was added to terminate the reaction and the optical density (OD) at 450 nm was measured within 15 min.
After mice were sacrificed, their entire heads and spleens were soaked in 10% neutral formalin fixative for 24 h, because the nasal cavity of BALB/c mice is small. Afterwards, the heads were soaked in 0.5 M ethylene diamine tetraacetic acid for decalcification for 4 weeks. After the mouse skull was softened, the tissues were conventionally dehydrated, embedded in paraffin, and sectioned in the coronal position (about 3 μm thick slices). The histopathological changes of the nasal mucosa were visualized with hematoxylin–eosin staining. The same steps were applied to the spleens.
At least three independent experiments were performed for each experimental condition. Data were analyzed by GraphPad Prism 5 software and are shown as mean ± SEM. In addition, two-tailed, unpaired Student t-tests were used. Animals were randomly assigned during collection, but the data analysis was single-masked.
Characterization of MSCs-Exo
MSCs-Exo have been recognized as a promising substitution for MSCs. Our size distribution analysis revealed that the MSCs-Exo were around 100 nm in diameter (Figure 1B). TEM analysis of the morphology further confirmed the exosomes’ identity (Figure 1A).
Intranasal delivery of MSCs-Exo relieves AR symptoms
We used an AR mouse model to investigate the role of MSCs-Exo in AR (Figure 2A). We measured the number of sneezing and nose rubbing motions during 10 min after the last intranasal administration of OVA. The results showed that the mice in the AR group sneezed and rubbed more frequently than those in the control group. Moreover, the numbers of sneezing and rubbing events were significantly lower in the MSCs-Exo treatment group compared to the AR group (Figure 2B). In conclusion, intranasal treatment with MSCs-Exo could notably reduce sneezing and rubbing frequencies, thus indicating that MSCs-Exo could relieve the symptoms in AR mice.
Intranasal delivery of MSCs-Exo reduces AR inflammation
To further understand the effects of MSCs-Exo on AR, the levels of different inflammation-related indicators were measured. As shown in Figure 2C, sections of the control group revealed normal nasal cavity mucosa. In the AR group, we observed more infiltrating eosinophils and lymphocytes, glandular secretion, and mucosal swelling (Figure 2D). After MSCs-Exo treatment, there were significantly fewer infiltrating cells and less glandular secretion and mucosal swelling in the nasal mucosa (Figure 2E). Additionally, the quantification of eosinophils (Figure 2F) suggested that MSCs-Exo have a therapeutic effect on AR mice. The spleen index, which also reflects the inflammatory status, demonstrated similar differences between the three groups (Figure 3A). Spleen sections from different groups are shown in Figure 3B–D. We observed apparent splenic sinus edema, splenic capsule incrassation, and vasodilation in the AR group (Figure 3C), and MSCs-Exo administration reduced inflammation.
The cytokine levels in the spleen, including Th2 cytokines (IL-4, IL-5, IL-6, IL-10, IL-13, and TGF-β), a Th1 cytokine (IFN-γ), a Th17 cytokine (IL-17), an eosinophil chemoattractant (CCL-11)20, and an adhesion receptor (ICAM-1)21, were analyzed by RT-PCR at 24 h after the last treatment. As shown in Figure 4A, IL-4, IL-5, IL-6, IL-13, CCL-11, and ICAM-1 levels were significantly decreased in the MSCs-Exo group compared to the AR group. While there were no differences in IL-17 and TGF-β levels, IL-10 and IFN-γ levels were obviously enhanced in the MSCs-Exo group compared to the AR group. The serum concentrations of histamine, OVA-IgE, IgE, IgG1, and IgG2a, and the concentrations of histamine, OVA-IgE, and IgG1 in bronchoalveolar lavage fluid (BALF), were measured by ELISA. The MSCs-Exo mice expressed low levels of OVA-IgE, IgE, and IgG1, but not IgG2a (Figure 4B and C). These results verify our hypothesis that intranasal delivery of MSCs-Exo could inhibit allergic airway inflammation and regulate the balance of Th1/Th2 in OVA-sensitized mice.
Optimal concentration of MSCs-Exo
After clarifying the therapeutic effect of MSCs-Exo, we used different concentrations of MSCs-Exo to find the optimal concentration for AR treatment. We used 4×106/mL, 4×107 /mL, 4×108/mL, 4×109/mL, and 4×1010/mL exosomes for intranasal administration in AR mice (Figure 5A). We found that the effect was dose-dependent (Figure 5B–E). At a concentration of 4×106/mL, we observed basically no effect on the sneezing and rubbing events and inflammation-related indicators. At concentrations higher than 4×108/mL, no significant further improvement in the inflammatory symptoms of the mice was observed. This result suggests that the optimal concentration of MSCs-Exo to reduce allergic inflammation in mice is around 4×108/mL.
MSCs-EXO suppress inflammation via the MAPK pathway
As shown in Figure 6, the mRNA levels of JUN, FOS, ERK, JNK, IKB, and IKK were significantly higher in the AR group than in the control group, while the mRNA levels of JUN, FOS, ERK, and JNK were significantly lower in the MSCs-Exo group than in the AR group but higher than in the control group. Furthermore, there were no differences in the mRNA levels of IKK and IKB between the AR group and the MSCs-Exo group. These results imply that AR might stimulate inflammation by activating the MAPK and NF-κB pathways, while MSCs-Exo alleviates inflammation by inhibiting the MAPK pathway.
We have verified that the AR mouse model was successfully established. We first showed that intranasal delivery of MSCs-Exo could not only relieve the main AR symptoms, sneezing and runny nose, but also decrease various inflammation indicators, including the spleen index, tissue staining, and the expression of inflammation-related cytokines. Moreover, we found that the optimal concentration of MSCs-Exo was 4×108/mL. Besides, we demonstrated that the MAPK and NF-κB pathways play an important role in inflammation, and that MSCs-Exo ameliorated AR by inhibiting the expression of MAPK pathway proteins, which modulated the immune response in the AR mouse model.
MSCs exert immunoregulatory effects by inhibiting T cell proliferation, inactivating allogeneic T cells, influencing T cell apoptosis22, and inhibiting B cell proliferation to decrease antibody secretion23. Furthermore, MSCs inhibit the differentiation and maturation of dendritic cells, resulting in a decline in the ability to activate T cells24. MSCs exert the above immunomodulatory effects mainly through the paracrine secretion of exosomes25. The presence of microvilli and columnar cells in the nasal cavity can intensify drug absorption26, and intranasal administration is not only safe but also convenient to operate. These advantages increase its feasibility for clinical application. Therefore, we chose to study the therapeutic effect of MSCs-Exo on AR by intranasal delivery; our results verify that intranasal administration of MSCs-Exo works not only locally but also systemically.
After exposure to the specific allergen, IgE mediates mast cell degranulation, causing itching and sneezing and further promoting hemangiectasis and increasing secretion of submucosal glands, thus resulting in obstruction and rhinorrhea. The immunohistological characteristics of AR include the infiltration of eosinophils and the predominant expression of cytokines secreted by Th2 cells, with a reduced activity level of Th1 cells, which contributes to the late-phase response such as nasal obstruction and hyperreactivity27, 28. Our results correspond with the mechanism underlying AR described above. In the AR model, IgE, OVA-IgE, IgG1, and histamine levels in BALF and serum and Th2 cytokine levels increased, corresponding to severe local and systematic symptoms. After intranasal administration of MSCs-Exo, the decrease in IgE, OVA-IgE, and histamine levels relieved the classic symptoms; the decrease in CCL-11 levels is linked to lower eosinophil infiltration; the change in ICAM-1 and Th2 cytokine levels is linked to reduced inflammation; and increased IFN-γ levels can stimulate the expression of IgG2a and inhibit the production of IgG3, IgG1, IgG2b, and IgE29, thus further exerting a therapeutic effect on AR. Many studies have also demonstrated that after intravenous treatment with different kinds of exosomes in an asthma mouse model, inflammation of lung tissues decreased, and Th2 cytokine and inflammatory cytokine levels were lower in serum and BALF30-32. All these results imply that intranasal delivery of MSCs-Exo has an effect similar to that of intravenous delivery to suppress allergic reactions.
In order to pave the way for clinical application in the near future, we examined the effects of different doses, and found that the optimal concentration is 4×108/mL. When the concentration of MSCs-Exo is lower than 4×108/mL, the efficacy decreases significantly. Once the concentration is higher than 4×108/mL, the curative effects do not further increase significantly. The data show that MSCs-Exo works in a dose-dependent manner, which supports future clinical research.
The activation of NF-κB plays an important role in allergic diseases, inducing the accumulation of inflammatory cells33. When activated by inflammatory signals, the released NF-κB induces the transcription of many inflammatory cytokines, which are related to the pathogenesis of asthma34. MAPKs are involved in many different cellular events, including allergic diseases35. Mammalian MAPKs are mainly divided into three categories: extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p3836. The activation of MAPK is critical for the production of inflammatory cytokines37, and functional differentiation into Th1 or Th2 subsets38. Notably, inhibition of ERK promotes the transition of Th2 lymphocytes to Th139. Our results showed that the expression of genes related to the NF-κB and MAPK pathways increased significantly in AR mice, but after MSCs-Exo treatment, the expression of genes related to the NF-κB pathway did not decrease significantly, while MSCs-Exo treatment significantly inhibits ERK, JNK, JUN, and FOS expression. The results confirm that the NF-κB and MAPK pathways play important roles in AR and indicate that MSCs-Exo do not reduce the activation of NF-κB to alleviate the symptoms of AR. MSCs-Exo inhibit inflammation by restricting OVA from affecting the MAPK pathway in AR mice.
While our results have demonstrated that intranasal delivery of MSCs-Exo is an effective therapy for AR, the specific mechanism has not been adequately revealed. It has not been researched how the MAPK pathway regulates the expression of cytokines to play a therapeutic role in AR. The specific functional components of MSCs-Exo have not been identified, and it is unknown how long they remain active. Previously, the effects of intranasal and intravenous delivery of MSCs-Exo on the brain were compared, and intranasal delivery was more effective40. For AR, no direct comparisons between intravenous and intranasal delivery have been made. Note also that we only studied intranasal administration of MSCs-Exo isolated from human umbilical cord; and while this extends the current treatment methods, it will be interesting to test exosomes secreted by other cells to examine the different effects.
Intranasal administration of MSCs-Exo has been researched in various diseases, including complete spinal cord injury41, microglia-mediated neuroinflammation42, and autism spectrum disorders43. It is noteworthy that intranasal delivery of MSC-Exo could substantially expand pulmonary IL-10-producing interstitial macrophages to protect against allergic asthma in mice44. However, research on intranasal delivery of MSC-Exo in AR is still scarce. Our results offer a theoretical and experimental basis for the future clinical local application of MSCs-Exo in the nasal cavity for the treatment of AR, which can effectively alleviate pain in AR patients and has significant clinical and social value.
In conclusion, the effect of exosomes on AR has firstly been investigated in this study, we found that intranasal administration of MSCs-Exo could not only reduce the behavior of nasal scratching and sneezing in mice, but also cause a decline in related immune indicators via the MAPK pathway. The significant beneficial effects of exosomes may provide a new, non-invasive treatment strategy for AR.
AR: Allergic rhinitis
MSCs: Mesenchymal stem cells
MSCs-Exo: MSC-derived exosomes
OVA-sIgE: ovalbumin-specific IgE
TEM: transmission electron microscopy
OD: optical density
BALF: bronchoalveolar lavage fluid
ERK: extracellular signal-regulated kinase
JNK: c-Jun N-terminal kinase
This work was supported by grants from Nanjing Medical Science and Technique Development Foundation (QRX17051, YKK20070) and the Project of Invigorating Health Care Through Science, Technology and Education (ZDXKB2016015). We also thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.
CY, YC, BW, XC, and XG conceived and designed the experiments. CY, YC, XX, XD, SL, HW, XW and ZX performed the experiments. CY, YC, XX, XD, SL, BW, XC, and XG analyzed the data. CY, YC, BW, XC, and XG wrote the paper. All authors read and approved the final manuscript.
Supported by grants from Nanjing Medical Science and Technique Development Foundation (QRX17051, YKK20070) and the Project of Invigorating Health Care Through Science, Technology and Education (ZDXKB2016015).
Availability of data and materials
All data generated or analyzed during this study are available from the corresponding author upon reasonable request.
Ethics approval and consent to participate
The animal procedures were approved by the Animal Care and Use Committee of Nanjing Medical University and animals were treated following the National Institutes of Health Guide for the Care and Use of Laboratory Animals. All operations were carried out in accordance with the approved procedures. All umbilical cord samples were taken after informed and written consent, and the study was approved by the Research Ethics Board of Nanjing Drum Tower Hospital (permit number 2017-161-01).
Consent for publication
The authors declare no competing interests.
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