佐藤 峻

In hypoxic pulmonary hypertension (PH), pulmonary vascular remodeling is characterized by the emergence of activated adventitial fibroblasts, leading to medial smooth muscle hyperplasia. Previous studies have suggested that CD26/dipeptidyl peptidase-4 (DPP4) plays a crucial role in the pathobiological processes in lung diseases. However, its role in pulmonary fibroblasts in hypoxic PH remains unknown. Therefore, we aimed to clarify the mechanistic role of CD26/DPP4 in lung fibroblasts in hypoxic PH. Dpp4 knockout (Dpp4 KO) and wild-type (WT) mice were exposed to hypoxia for 4 weeks. The degree of PH severity and medial wall thickness was augmented in Dpp4 KO mice compared with that in WT mice, suggesting that CD26/DPP4 plays a suppressive role in the development of hypoxic PH. Transcriptome analysis of human lung fibroblasts cultured under hypoxic conditions revealed that TGFB2, TGFB3, and TGFA were all upregulated as differentially expressed genes after DPP4 knockdown with small interfering RNA treatment. These results suggest that CD26/DPP4 plays a suppressive role in TGFβ signal-regulated fibroblast activation under hypoxic conditions. Therefore, CD26/DPP4 may be a potential therapeutic target in patients with PH associated with chronic hypoxia.

Acute respiratory distress syndrome (ARDS) is characterized by dysregulated inflammation and increased permeability of lung microvascular cells. CD26/dipeptidyl peptidase-4 (DPP4) is a type II membrane protein that is expressed in several cell types and mediates multiple pleiotropic effects. We previously reported that DPP4 inhibition by sitagliptin attenuates lipopolysaccharide (LPS)-induced lung injury in mice. The current study characterized the functional role of CD26/DPP4 expression in LPS-induced lung injury in mice, isolated alveolar macrophages, and cultured lung endothelial cells. In LPS-induced lung injury, inflammatory responses [bronchoalveolar lavage fluid (BALF) neutrophil numbers and several proinflammatory cytokine levels] were attenuated in Dpp4 knockout (Dpp4 KO) mice. However, multiple assays of alveolar capillary permeability were similar between the Dpp4 KO and wild-type mice. TNF-α and IL-6 production was suppressed in alveolar macrophages isolated from Dpp4 KO mice. In contrast, in cultured mouse lung microvascular endothelial cells (MLMVECs), reduction in CD26/DPP4 expression by siRNA resulted in greater ICAM-1 and IL-6 expression after LPS stimulation. Moreover, the LPS-induced vascular monolayer permeability in vitro was higher in MLMVECs treated with Dpp4 siRNA, suggesting that CD26/DPP4 plays a protective role in endothelial barrier function. In summary, this study demonstrated that genetic deficiency of Dpp4 attenuates inflammatory responses but not permeability in LPS-induced lung injury in mice, potentially through differential functional roles of CD26/DPP4 expression in resident cellular components of the lung. CD26/DPP4 may be a potential therapeutic target for ARDS and warrants further exploration to precisely identify the multiple functional effects of CD26/DPP4 in ARDS pathophysiology.NEW & NOTEWORTHY We aimed to clarify the functional roles of CD26/DPP4 in ARDS pathophysiology using Dpp4-deficient mice and siRNA reduction techniques in cultured lung cells. Our results suggest that CD26/DPP4 expression plays a proinflammatory role in alveolar macrophages while also playing a protective role in the endothelial barrier. Dpp4 genetic deficiency attenuates inflammatory responses but not permeability in LPS-induced lung injury in mice, potentially through differential roles of CD26/DPP4 expression in the resident cellular components of the lung.

Pulmonary hypertension (PH) with interstitial lung diseases (ILDs) often causes intractable conditions. CD26/Dipeptidyl peptidase-4 (DPP4) is expressed in lung constituent cells and may be related to the pathogenesis of various respiratory diseases. We aimed to clarify the functional roles of CD26/DPP4 in PH-ILD, paying particular attention to vascular smooth muscle cells (SMCs). Dpp4 knockout (Dpp4KO) and wild type (WT) mice were administered bleomycin (BLM) intraperitoneally to establish a PH-ILD model. The BLM-induced increase in the right ventricular systolic pressure and the right ventricular hypertrophy observed in WT mice were attenuated in Dpp4KO mice. The BLM-induced vascular muscularization in small pulmonary vessels in Dpp4KO mice was milder than that in WT mice. The viability of TGFβ-stimulated human pulmonary artery SMCs (hPASMCs) was lowered due to the DPP4 knockdown with small interfering RNA. According to the results of the transcriptome analysis, upregulated genes in hPASMCs with TGFβ treatment were related to pulmonary vascular SMC proliferation via the Notch, PI3K-Akt, and NFκB signaling pathways. Additionally, DPP4 knockdown in hPASMCs inhibited the pathways upregulated by TGFβ treatment. These results suggest that genetic deficiency of Dpp4 protects against BLM-induced PH-ILD by alleviating vascular remodeling, potentially through the exertion of an antiproliferative effect via inhibition of the TGFβ-related pathways in PASMCs.

BACKGROUND AND OBJECTIVE: The possibility of combination therapy with atomoxetine (ATO) and oxybutynin (OXY) has been suggested for obstructive sleep apnoea (OSA). However, the effectiveness of this treatment remains uninvestigated in Japanese OSA patients. Therefore, we performed a randomized, crossover, phase II, single-centre prospective trial to examine the effects of ATO-OXY therapy in Japanese OSA patients. METHODS: In total, 17 OSA patients participated in this study. The effects of one night of 80-mg ATO plus 5-mg OXY administration were compared with those of no medication administered before sleep. The primary and secondary outcomes comprised the apnoea-hypopnoea index (AHI) and nadir SpO2 , SpO2 drop time and sleep architecture, respectively. The safety endpoints included drug side effects and adverse events. RESULTS: The values of AHI, nadir SpO2 , 3% oxygen desaturation index (ODI), 4% ODI, and SpO2 drop time of <90% did not significantly differ between patients receiving ATO-OXY administration and no medication. Sleep architecture exhibited a significant change: ATO-OXY increased sleep stage N1 (p < 0.0001) and decreased stage N2 (p = 0.03), rapid eye movement (p < 0.0001) and sleep efficiency (p = 0.02). However, the subanalysis demonstrated an obvious decrease in AHI in five responder patients. Total sleep time and basal sleep efficiency tended to be lower in the responders compared with nonresponders (p = 0.065). No patients experienced severe adverse events or side effects. CONCLUSION: Overall, ATO-OXY therapy does not reduce AHI in Japanese OSA patients, although AHI was decreased in a proportion of patients. Future studies for identifying treatment response group characteristics are warranted.

The pathogenesis of pulmonary fibrosis involves complex interplay between cell types and signaling pathways. Recurrent alveolar epithelial injury can occur during pulmonary inflammation, causing dysregulation of epithelial repair. Dysregulated repair interacts with mesenchymal, inflammatory, and endothelial cells to trigger fibroblast-to-myofibroblast activation. CD26/dipeptidyl peptidase-4 (DPP4) is a type II membrane protein mediating pleiotropic effect. However, the mechanistic role of CD26/DPP4 in pulmonary fibrosis remains unclear. In this study, we aimed to characterize Dpp4 deficiency in a mouse bleomycin (BLM)-induced pulmonary fibrosis model and in cell culture systems of human lung fibroblasts (HLFs). Dpp4 knockout (Dpp4 KO) mouse lungs exhibited lower Ashcroft scale indices, collagen content, and numbers of fibroblasts and myofibroblasts compared with those in C57BL/6 wild-type (WT) mice. Upregulation of Tgfb1 and Tgfb2 mRNA levels in the lungs after BLM treatment was lower in Dpp4 KO mice compared with those in WT mice. Although TGF-β-driven endothelial-to-mesenchymal transition (EndMT) has been implicated as one of the mechanisms of pulmonary fibrosis, a number of partial EndMT cells in lungs did not differ between Dpp4 KO mice and WT mice. The proliferation capacity and mRNA levels of COL1A1, a collagen deposition-related gene, in cultured HLFs were suppressed in DPP4 small interfering RNA-treated cells. This study indicates that the genetic deficiency of DPP4 has protective effects against BLM-induced pulmonary fibrosis, partly through the reduction in TGF-β expression and inhibition of fibroblast activation in the lung. Our study suggests that CD26/DPP4 inhibition is a potential therapeutic strategy for pulmonary fibrosis.