The hippo and the nose
Reviewed by Hassan Mohammed

Chronic rhinosinusitis with nasal polyps (CRSwNP) leads to histological changes including thickening of the basilar membrane and epithelial proliferation. Molecular mechanisms underlying these changes are still not fully clear. A signalling pathway called the hippo with Yes‐associated protein (YAP) as its main effector has been suggested to have a role in the differentiation and proliferation of airway epithelial cells. Its role in CRSwNP, however, remains unknown. The authors processed biopsies from polyps of 14 non-eosinophilic CRSwNP patients, 14 eosinophilic CRSwNP patients and inferior turbinates of 14 controls. None of the included subjects had any steroids or antibiotics in the three months preceding biopsy and none had systemic disease. Western blot, real-time PCR, cell culture and immunofluorescence were used to test for hippo pathway products. In both eosinophilic and non-eosinophilic CRSwNP patients there was significant upregulation of mRNA levels of YAP, significant increase in hippo pathway protein components, significant increase in epithelial levels of YAP and in the thickness of the basilar membrane. The authors found moderate to strong correlations between YAP expression and the visual analogue score, Lund‐Mackay CT score and Lund‐Kennedy endoscopic score in CRSwNP patients. They concluded that there is evidence that the hippo pathway and its core effector YAP play a role in promoting epithelial proliferation and differentiation in CRSwNP. This means that the hippo‐YAP pathway could be a therapeutic target in solving nasal epithelial remodelling. Additionally, YAP expression could be a useful histological marker for disease severity in patients with CRSwNP. The main limitation of the study is the small number of samples. However, it is still an interesting study highlighting potential therapeutic targets for CRSwNP.

The hippo pathway effector Yes‐associated protein promotes epithelial proliferation and remodeling in chronic rhinosinusitis with nasal polyps.
Deng H, Sun Y, Wang W, et al.
ALLERGY
2019;74:731-42.