Evolutionary conservation of the antimicrobial function of mucus: a first defence against infection

Abstract

Mucus layers often provide a unique and multi-functional hydrogel interface between the epithelial cells of organisms and their external environment. Mucus has exceptional properties including elasticity, changeable rheology and an ability to self-repair by re-annealing, and is therefore an ideal medium for trapping and immobilising pathogens and serving as a barrier to microbial infection. The ability to produce a functional surface mucosa was an important evolutionary step, which evolved first in the Cnidaria, which includes corals, and the Ctenophora. This allowed the exclusion of non-commensal microbes and the subsequent development of the mucus-lined digestive cavity seen in higher metazoans. The fundamental architecture of the constituent glycoprotein mucins is also evolutionarily conserved. Although an understanding of the biochemical interactions between bacteria and the mucus layer are important to the goal of developing new antimicrobial strategies, they remain relatively poorly understood. This review summarises the physicochemical properties and evolutionary importance of mucus, which make it so successful in the prevention of bacterial infection. In addition, the strategies developed by bacteria to counteract the mucus layer are also explored.

Tracheal brush cells release acetylcholine in response to bitter tastants for paracrine and autocrine signaling

“…Previously, M3R was found to be involved in cholinergic autocrine signaling in lingual taste buds. 45 MC represents the first step for removing potentially dangerous inhaled particles and bacteria from the airways. 4 A negative feedback loop mediated by M2R and M5R in response to bitter substances was reported for urethral BC and a possible role of this loop for bladder overreactivity was suggested.…”

“…7,25 Another important protective mechanism is activation of MC, the oldest evolutionary mechanism of innate immunity of the airways. 45 MC represents the first step for removing potentially dangerous inhaled particles and bacteria from the airways. Consistent with previous reports, 15,16,46 we have observed that MC is regulated by ACh and that this ACh-induced increase in cilia-driven PTS is M3Rdependent.…”

Towards bioinspiredin vitromodels of intestinal mucus

“…Intestinal mucus has at least two functions: it guarantees a perfect physical separation between bacteria and cells and it regulates the absorption of substances from the lumen, acting as a selective membrane. 59 In vitro models should display a thickness and a ratio between the thickness of the loose and attached layers comparable to native mucus, as these parameters are involved in the specic functions of the different intestinal tracts. 41 To elucidate the role of the mucus in drug delivery and symbiosis with bacteria, different models have been used 60 (Fig.…”

Insights into the evolution of digestive systems from studies of Trichoplax adhaerens

“…Reproduced from (Smith et al 2015) of food into the digestive cavity/tract and to expel undigestible material and feces. Mucous also protects the digestive epithelium from harmful molecules, such as digestive enzymes, and microorganisms (Bakshani et al 2018;Dias et al 2018;Liévin-Le Moal and Servin 2006). Mucocytes have not been reported in adult Porifera, but mucous-secreting cells are present in larval sponges (Homoscleromorpha-Ereskovsky et al 2007; Demospongiae- Leys and Degnan 2001).…”