1. ¹Division of Dermatology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
2. ²Department of Dermatology, Greater Los Angeles Healthcare System Veterans Affairs, Los Angeles, California, USA

Correspondence: Dr J Kim, Division of Dermatology, David Geffen School of Medicine at UCLA, 52–121 CHS, 10833 Le Conte Avenue, Los Angeles, CA 90095, USA. E-mail: jekim@mednet.ucla.edu

Received 19 December 2007; Revised 31 March 2008; Accepted 18 April 2008; Published online 19 June 2008.

Abstract

Propionibacterium acnes is a critical component in the pathogenesis of acne vulgaris, stimulating the production of various inflammatory mediators, such as cytokines and chemokines, important in the local inflammatory response found in acne. This study explored the role of P. acnes and its ability to induce matrix metalloproteinases (MMPs) in primary human monocytes and how this induction is regulated by retinoids. MMP-1- and MMP-9-expressing cells were present in perifollicular and dermal inflammatory infiltrates within acne lesions, suggesting their role in acne pathogenesis. In vitro, we found that P. acnes induced MMP-9 and MMP-1 mRNA, and the expression of MMP-9, but not of MMP-1, was found to be Toll-like receptor 2-dependent. P. acnes induced the mRNA expression of tissue inhibitors of metalloproteinase (TIMP)-1, the main regulator of MMP-9 and MMP-1. Treatment of monocytes with all-trans retinoic acid (ATRA) significantly decreased baseline MMP-9 expression. Furthermore, co-treatment of monocytes with ATRA and P. acnes inhibited MMP-9 and MMP-1 induction, while augmenting TIMP-1 expression. These data indicate that P. acnes-induced MMPs and TIMPs may be involved in acne pathogenesis and that retinoic acid modulates MMP and TIMP expression, shifting from a matrix-degradative phenotype to a matrix-preserving phenotype.