Mucin 4 Glycoprotein Appears to Play an Important Role in Coronavirus Disease

Many surfaces of our body, including the surface of the respiratory system (from the nose to the lung), eyes, ears, intestine and others, are covered by a layer called mucus. This mucus layer serves as the body's very first line of defence against pathogens (e.g. bacteria, viruses). The main components of mucus besides water are large glycoproteins called mucins. Mucins are highly glycosylated - glycans account for 50-80% of the molecular weight of mucins. More than 20 mucins have been identified in humans, for example just in the lung 16 mucins have been identified (Mucin 1, Mucin 2, Mucin 4, Mucin 5AC, Mucin 5B, Mucin 7, Mucin 8, Mucin 11, Mucin 13, Mucin 15, Mucin 16, Mucin 18, Mucin 19, Mucin 20, Mucin 21 and Mucin 22). Mucins limit infection by different pathogens not only by providing a physical barrier but also through initiation of intracellular signalling in response to the pathogen that modulates the immune response.

Mucin 4 glycoprotein (Adapted from the Atlas of Genetics and Cytogenetics in Oncology and Haematology)

New research suggests that one of the mucin glycoproteins - Mucin 4 seems to be highly relevant for coronavirus disease. The research showed that the absence of Mucin 4 glycoprotein led to more severe disease following infection with SARS-CoV virus. It should be pointed out that this research was conducted in mice but may shed some light on the role of mucin glycoproteins in susceptibility to coronavirus infection and in determining the severity and outcome of the disease. It should be also pointed out that in this research the relevance of Mucin 4 protein for coronavirus disease was demonstrated only in female mice  – only female mice lacking Mucin 4 consistently demonstrated increased disease severity following infection with SARS-CoV virus, while males did not. That is interesting considering the fact that the epidemiological data of individuals with confirmed SARS-CoV-2 infection also shows some clear sex differences – more men than women have been infected by SARS-CoV-2 virus and the mortality rates of COVID-19 have been higher among men than women.

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