Efforts to study acne have been hindered by lack of an animal model that replicates the human condition. When administered to mice, the bacterium Propionibacterium acnes, believed to be the causative agent of acne, is cleared away rapidly with no long-term effects on the skin. Now, researchers at the University of California San Diego School of Medicine, Cedars-Sinai and UCLA have developed a new mouse model that closely resembles human acne by adding a synthetic sebum—a waxy skin secretion that increases in human adolescence. Their results are published in JCI Insight.
The bacterium Propionibacterium acnes is plentiful on everyone’s skin so why people experience acne to varying degrees or not at all has been a source of mystery. Through genetic sequencing it was recently determined that not all strains of P. acnes are the same, offering a clue as to why these differences may be.
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Using the new animal model, the authors of the current study were able to compare “good” (health-associated) and “bad” (acne-associated) strains of P. acnes. This allowed them to study what it is about the acne-associated strains that allow them to cause skin lesions.
The study was performed by inoculating mice with P. acnes and applying fresh sebum daily. The sebum they created for the model consisted of four ingredients—fatty acid, triglyceride, wax and squalene—in ratios that mimic human sebum.
When both sebum and acne-associated strains of P. acnes was applied, they saw effects resembling human acne, and the bacteria survived for weeks. These strains also caused skin inflammation, measured via elevated levels of cytokines.
When this was done with health-associated strains of P. acnes, the same amount of bacteria was still present on the skin, but lesions caused by these bacteria scored approximately two times lower than lesions caused by the acne-associated strains. The scoring measured lesion’s size, redness, dryness, and degree of skin sloughing.
These results offer additional evidence to the origins of acne and lead to insights that could help in determining who is at risk for acne and how to develop personalized treatments that target acne-promoting bacterial factors or sebum components.
Image: Mouse skin treated with synthetic human sebum, administered with strains of either acne-associated P. acnes (left) or health-associated P. acnes (right), and viewed under a microscope. Image courtesy of UC San Diego Health.