SPLUNC1 α6 Peptidomimetic: A Novel Therapeutic for Asthma

Sodium Houttuyfonate Alleviates Monocrotaline-induced Pulmonary Hypertension by Regulating Orai1 and Orai2

An increased intracellular Ca2+ concentration ([Ca2+]i) is a key trigger for pulmonary arterial smooth muscle cell (PASMC) proliferation and contributes greatly to pulmonary hypertension (PH). Extracellular Ca2+ influx via a store-operated Ca2+ channel, termed store-operated Ca2+ entry (SOCE), is a crucial mechanism for [Ca2+]i increase in PASMCs. Calcium release-activated calcium modulator (Orai) proteins, consisting of three members (Orai1-3), are the main components of the store-operated Ca2+ channel. Sodium houttuyfonate (SH) is a product of the addition reaction of sodium bisulfite and houttuynin and has antibacterial, antiinflammatory, and other properties. In this study, we assessed the contributions of Orai proteins to monocrotaline (MCT)-enhanced SOCE, [Ca2+]i, and cell proliferation in PASMCs and determined the effect of SH on MCT-PH and the underlying mechanism, focusing on Orai proteins, SOCE, and [Ca2+]i in PASMCs. Our results showed that: 1) Orai1 and Orai2 were selectively upregulated in the distal pulmonary arteries and the PASMCs of MCT-PH rats; 2) knockdown of Orai1 or Orai2 reduced SOCE, [Ca2+]i, and cell proliferation without affecting their expression in PASMCs in MCT-PH rats; 3) SH significantly normalized the characteristic parameters in a dose-dependent manner in the MCT-PH rat model; and 4) SH decreased MCT-enhanced SOCE, [Ca2+]i, and PASMC proliferation via Orai1 or Orai2. These results indicate that SH likely exerts its protective role in MCT-PH by inhibiting the Orai1,2-SOCE-[Ca2+]i signaling pathway.

CC16 drives VLA-2-dependent SPLUNC1 expression

Rationale

CC16 (Club Cell Secretory Protein) is a protein produced by club cells and other non-ciliated epithelial cells within the lungs. CC16 has been shown to protect against the development of obstructive lung diseases and attenuate pulmonary pathogen burden. Despite recent advances in understanding CC16 effects in circulation, the biological mechanisms of CC16 in pulmonary epithelial responses have not been elucidated.

Objectives

We sought to determine if CC16 deficiency impairs epithelial-driven host responses and identify novel receptors expressed within the pulmonary epithelium through which CC16 imparts activity.

Methods

We utilized mass spectrometry and quantitative proteomics to investigate how CC16 deficiency impacts apically secreted pulmonary epithelial proteins. Mouse tracheal epithelial cells (MTECS), human nasal epithelial cells (HNECs) and mice were studied in naïve conditions and after Mp challenge.

Measurements and main results

We identified 8 antimicrobial proteins significantly decreased by CC16-/- MTECS, 6 of which were validated by mRNA expression in Severe Asthma Research Program (SARP) cohorts. Short Palate Lung and Nasal Epithelial Clone 1 (SPLUNC1) was the most differentially expressed protein (66-fold) and was the focus of this study. Using a combination of MTECs and HNECs, we found that CC16 enhances pulmonary epithelial-driven SPLUNC1 expression via signaling through the receptor complex Very Late Antigen-2 (VLA-2) and that rCC16 given to mice enhances pulmonary SPLUNC1 production and decreases Mycoplasma pneumoniae (Mp) burden. Likewise, rSPLUNC1 results in decreased Mp burden in mice lacking CC16 mice. The VLA-2 integrin binding site within rCC16 is necessary for induction of SPLUNC1 and the reduction in Mp burden.

Conclusion

Our findings demonstrate a novel role for CC16 in epithelial-driven host defense by up-regulating antimicrobials and define a novel epithelial receptor for CC16, VLA-2, through which signaling is necessary for enhanced SPLUNC1 production.