Non-coding RNAs Analysis of Eosinophil Subtypes in Asthma

Chronic airway inflammation rich in eosinophils is an important feature seen in asthma. Airway and blood eosinophilia is associated with increased rates of asthma exacerbations and more intense treatment. Recently, the existence of two distinct eosinophils subtypes was revealed-lung-resident eosinophils (rEOS), which maturate independently to interleukin (IL) 5, with the primary function to maintain tissue homeostasis, and inflammatory eosinophils (iEOS), which mature in IL-5-dependent manner and are mainly involved in immune responses. Eosinophils' effect on the airway remodeling in asthma depends not only on the activity but also by their viable number in the lungs. Blood iEOS infiltrate the airways mainly after the environmental stimulus like allergen and leave the airways with bronchial secretions. However, rEOS reside lung tissue for their entire lifetime regulating local immunity. Blood rEOS and iEOS ratio alters in asthma, compared with healthy controls. It is known that the predominant eosinophils subtype in allergic asthma are iEOS, while rEOS are basic subtype in severe eosinophilic asthma patients, moreover, they are different in adhesive properties and survivability as well. Distinct biological properties allows to speculate about their different functions in asthma, however, there are still little information. Data about differently expressed microRNA (miRNA) profiles in eosinophils in asthma suggests, that eosinophils subtypes can be distinct in non-coding RNA (ncRNA) - microRNA (miRNA), piwi-interacting RNA (piRNA) and long non-coding RNA (IncRNA) profiles that could describe their role in asthma pathogenesis and act as biomarkers to discern asthma phenotypes.

Asthma is not cured, and only well-balanced treatment can control the course and severity of the disease. Most clinical symptoms rise from aberrant chronic airway inflammation mostly eosinophilic. Eosinophils are terminally differentiated granulocytes that actively contribute to innate and adaptive inflammatory cascades through the production and release of diverse chemokines, cytokines, lipid mediators and other growth factors. IL-5 plays a fundamental role in eosinophils maturation in the bone marrow, their recruitment, and activation at sites of inflammation. Historically eosinophils were described as a critical player in host defense, including parasites, viruses, fungi, or bacteria, giving them a destructive inflammatory cell label. However, it became clear that steady-state eosinophils can contribute to the immunoregulation and tissue homeostasis as well. Studies revealed that there are distinct eosinophils subtypes - immunoregulatory lung-resident eosinophils (rEOS) and inflammatory eosinophils (iEOS), involved in immune responses. Distinct eosinophils subtypes with different functions determines the separate treatment. There are still only a few studies describing distinct eosinophils subtypes in the lungs or blood. It is the beginning of a new promising research area for better individualized eosinophilic asthma treatment, moreover, other eosinophilic diseases as well. Peripheral blood eosinophils studies are sufficiently relevant to the tissue eosinophils studies, as blood eosinophils are released into the bloodstream in a fully maturated form. Moreover, peripheral blood study could give additional information with possibilities to prevent eosinophils effects in the early stage, before migration to the airways. Furthermore, the existence of tissue-resident eosinophils in peripheral blood is confirmed and primary research for eosinophil subtypes surface markers was made according to the data of human blood eosinophils. Data about differently differently expressed microRNA (miRNA) profiles in eosinophils in asthma suggests, that eosinophils subtypes can be distinct in non-coding RNA (ncRNA) - microRNA (miRNA), piwi-interacting RNA (piRNA) and long non-coding RNA (IncRNA) profiles that could describe their role in asthma pathogenesis and act as biomarkers to discern asthma phenotypes. Researchers have plan to expand research by analyzing non-coding RNA (ncRNA) - miRNA, piRNA and lncRNA profiles of rEOS and iEOS as well as selected ncRNA signatures in blood plasma estimating their diagnostic value. Moreover, additional investigation of ncRNA in eosinophil-derived exosomes will provide important data about possible effect of eosinophils subtypes on airway remodeling via secreted ncRNA. ncRNAs are key regulators for gene transcription. However, there is evidence about their dysregulation in eosinophils during asthma. It will give important information about molecular signaling pathways that regulate the activity of distinct eosinophil subtypes during health and asthma, and provide the essential information about possible new therapeutic targets for their control. Additionally researchers will investigate the biological differences between rEOS and iEOS, including surface integrins and eosinophilopoietins receptors expression, adhesive properties, survivability, synthesized reactive oxygen species and apoptosis, as well as their effect on pulmonary structural cells physiological activity as proliferation, apoptosis, migration, contractility and proteins production, and will relate it with molecular signaling pathways, regulated by distinct expressed ncRNAs. ncRNAs can be stored in eosinophils exosomes and expressed to the surrounding environment. Information about ncRNAs in eosinophils-derived exosomes will demonstrate their function by affecting the other cells, especially after migration to airways. Moreover, ncRNAs are stable and resistant to blood RNases and differentially expressed in several pathologies. Researchers suppose that altered blood levels of ncRNAs could act as a possible new diagnostic biomarker in asthma.