Publikationsdatenbank

Expression analyses of CLCA members in the feline respiratory tract:
biomolecules in feline asthma? (2021)

Art

Hochschulschrift

Autor

Erickson, Nancy Ann (WE 12)

Quelle

Berlin: Mensch & Buch Verlag, 2021 — XII, 132 Seiten

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/31630

Kontakt

Institut für Tierpathologie

Robert-von-Ostertag-Str. 15
14163 Berlin
+49 30 838 62450
pathologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Certain members of the highly conserved chloride channel regulator, calcium-activated (CLCA) family have been implicated in inflammatory mucus-based respiratory conditions such as asthma, chronic obstructive pulmonary disease or cystic fibrosis which may either occur naturally or may be experimentally induced in animal species to model the respective human disease. CLCA1, the most intensively investigated member of this family to date, was shown to be highly expressed in these respiratory diseases and had been discussed as a therapeutic target. The CLCA family has been systematically characterized in naive and diseased conditions in humans and mice, and, to a lesser extent, in horses and naive pigs. It has not only revealed strong similarities but also distinct species-specific differences in genetic organization or protein structure and expression pattern, with partially functional contradictory results, particularly between human and murine CLCA orthologs. These interspecies differences are further complicated by possible redundancies or compensatory effects of homologous CLCA members and may limit the value of mouse models. Hence, caution is warranted in translating results from one species to another. Asthma is a highly relevant and naturally occurring disease not only in horses but also in cats, in which it shares many characteristics with the human disease. The feline CLCA family is, however, unknown to date. Hence, this study aimed at characterizing the gene and protein structure of the CLCA family in comparison to the orthologs of other well-investigated species, i.e. humans, mice, and pigs. Furthermore, it aspired at elucidating the mRNA and protein expression profile of feline CLCA members in healthy cats for the first time, particularly in the respiratory tract. Last but not least, it aimed gathering first evidence of allegedly differential expressional regulation of CLCA1 in feline asthma. It could be shown that the feline CLCA orthologs are grouped into four clusters, identical to all other species investigated to date with typical conservation of CLCA1 and CLCA2 on the genomic level. However, the cat possesses single and fully functional CLCA members not only in clusters 1 and 2 but, in contrast to all other species, both in clusters 3 and 4, which, hence, makes the cat particularly relevant in studying these individual CLCA members. Regarding CLCA1, the feline ortholog not only shows an identical genetic and protein structure as compared to the other species investigated, but also concerning its tissue expression pattern. In the naive respiratory tract, CLCA1 immunohistochemically localized to virtually all mucus cells and was found to be secreted extracellularly mucus. This expression pattern identical to all other species analyzed to date may point toward a conserved function of CLCA1 in this microenvironment. However, feline CLCAA1 was not detected in submucosal glands in which it is expressed in all aforementioned species. This niche seems to be occupied by a different CLCA member, CLCA3, in the cat. Surprisingly and in contrast to all aforementioned species, feline CLCA2 was neither found in SMGs nor in any other cell type of the feline respiratory tract, hence, excluding any possible compensatory or synergistic effect of CLCA2 in the cat, as had been proposed for CLCA2 in other species, at least during homeostatic conditions. The allegedly soluble protein CLCA3 was primarily found in ciliated respiratory epithelial cells and, importantly, also in mucus-producing SMG cells of the upper respiratory tract, similar to its murine orthologs CLCA3a1 and -3a2. It therefore appears that in cats, CLCA3 may substitute for the lack of CLCA1 and CLCA2 specifically in SMGs, with possible overlapping functions in that microenvironment. Similar to mice, but in contrast to man and pigs, the feline respiratory tract was devoid of CLCA4 expression. In the airways of asthmatic cats, CLCA1 intensely labelled the entire bronchial mucus layer, identical to all other species exhibiting chronic respiratory conditions with increased mucus production. This seemingly increased CLCA1 secretion cat may indicate a similar function as considered for human asthma patients and respective animal models. It is suggestive of a role in feline asthma in which it may serve as a biomarker and/or therapeutic target and needs to be investigated in future studies in detail. However, fundamental species-specific differences of other CLCA family members on the genomic and protein level may also imply functional diversity in homeostatic and challenged airways and, hence, may modulate the respiratory conditions differently and thereby impede the translatability of animal models. Therefore, an in-depth understanding of the heterogeneity of this gene family is required, especially concerning the respiratory tract.