Psoriasis and gut microbiota: is there a connection?

The psoriasis is a skin disease that is identified by red, scaly patches that cover specific parts of the body. These can be a source of itching and irritation, with their intensity varying from one individual to another. They appear following a skin inflammation caused by a failure of the immune system. T lymphocytes produce inflammatory molecules (cytokines Il-17, Il-22, TNF-alpha, among others). These stimulate the proliferation of keratinocytes. The renewal period of these cells, normally three weeks, then becomes three days. This results in an accumulation of immature keratinocytes on the skin surface, increasing the thickness of the outer layer (the cornea), this is the phenomenon of hyperkeratosis.

The skin symptoms of psoriasis can affect any area of the body, from the ears to the tongue, including the genital areas which can lead to various clinical forms. However, the scaly plaques are generally located on the scalp, elbows and knees. They are sometimes accompanied by a rheumatism.

The microbiota is a collection of microorganisms that includes non-pathogenic viruses, bacteria, and fungi. These microorganisms contribute to numerous processes, both local and systemic. The gut microbiota is the most populated of all and is located in the small intestine and the colon.

The gut microbiota has numerous implications on general health. Among other things, it promotes the body's digestive, metabolic, and immune functions. An imbalance in the gut microbiota, also known as dysbiosis, can have various impacts on health. Could it be implicated in psoriasis?

Studies have shown that the gut microbiota exhibits alterations in patients suffering from psoriasis compared to the control group. The bacterium Akkermansia muciniphila has been particularly observed at a lower rate in patients with psoriasis. This bacterium would play a role in the pathogenesis of inflammatory diseases. It has also been demonstrated that a decrease in Faecalibacterium prausnitzii with an increase in Escherichia coli occurs during psoriasis. The Bacteroidia has been found in abundance in psoriatic patients while Firmicutes was predominant in the control group. These study results have supported the idea of the presence of a gut microbiota-skin axis which could particularly play a role in the pathogenesis of psoriasis.

A more recent study has revealed that the gut microbiota plays a role in homeostasis and the immune system and particularly in Th17 cells. Indeed, a dysbiosis can affect the activation of immune cells via the IL-23 / IL-17 signalling pathway and lead to the production of IL-22 and interferon gamma (IFN-γ), causing hyperproliferation of keratinocytes. All these changes in the composition of the gut microbiota influence the activation of the immune system and the skin inflammation associated with psoriasis.

Note: In the case of psoriasis, it is necessary to prioritise a diet that reduces intestinal permeability and to avoid consuming foods that exacerbate the symptoms.

HUANG L. & al. Dysbiosis of gut microbiota was closely associated with psoriasis. Science China Life Sciences (2018).

HSU D. K. & al. Role of skin and gut microbiota in the pathogenesis of psoriasis, an Q6 inflammatory skin disease. Medicine in Microecology (2020).

BUHAS M. C. & al. Gut Microbiota in Psoriasis. Nutrients (2022).