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Open Access Research article

Linked decreases in liver kinase B1 and AMP-activated protein kinase activity modulate matrix catabolic responses to biomechanical injury in chondrocytes

Freyr Petursson1, Matt Husa2, Ron June3, Martin Lotz4, Robert Terkeltaub1* and Ru Liu-Bryan1*

Author Affiliations

1 VA San Diego Healthcare System, Department of Medicine, University of California San Diego, 111K, 3350 La Jolla Village Drive, San Diego, CA 92161, USA

2 Department of Medicine, The Ohio State University, 480 Medical Center Drive, Columbus, OH 43210, USA

3 Mechanical and Industrial Engineering Department, Montana State University, PO Box 173800 Bozeman, MT 59717-3800, USA

4 The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA

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Arthritis Research & Therapy 2013, 15:R77  doi:10.1186/ar4254

Published: 25 July 2013

Abstract

Introduction

AMP-activated protein kinase (AMPK) maintains cultured chondrocyte matrix homeostasis in response to inflammatory cytokines. AMPK activity is decreased in human knee osteoarthritis (OA) chondrocytes. Liver kinase B1 (LKB1) is one of the upstream activators of AMPK. Hence, we examined the relationship between LKB1 and AMPK activity in OA and aging cartilages, and in chondrocytes subjected to inflammatory cytokine treatment and biomechanical compression injury, and performed translational studies of AMPK pharmacologic activation.

Methods

We assessed activity (phosphorylation) of LKB1 and AMPKα in mouse knee OA cartilage, in aging mouse cartilage (6 to 24 months), and in chondrocytes after mechanical injury by dynamic compression, via immunohistochemistry or western blot. We knocked down LKB1 by siRNA transfection. Nitric oxide, matrix metalloproteinase (MMP)-3, and MMP-13 release were measured by Griess reaction and ELISA, respectively.

Results

Knockdown of LKB1 attenuated chondrocyte AMPK activity, and increased nitric oxide, MMP-3 and MMP-13 release (P <0.05) in response to IL-1β and TNFα. Both LKB1 and AMPK activity were decreased in mouse knee OA and aged knee cartilage, and in bovine chondrocytes after biomechanical injury. Pretreatment of bovine chondrocytes with AMPK activators AICAR and A-769662 inhibited both AMPKα dephosphorylation and catabolic responses after biomechanical injury.

Conclusion

LKB1 is required for chondrocyte AMPK activity, thereby inhibiting matrix catabolic responses to inflammatory cytokines. Concurrent loss of LKB1 and AMPK activity in articular chondrocytes is associated with OA, aging and biomechanical injury. Conversely, pharmacologic AMPK activation attenuates catabolic responses to biomechanical injury, suggesting a potentially novel approach to inhibit OA development and progression.

Keywords:
osteoarthritis; cartilage; aging; MMP-3; nitric oxide