1. Department of Medicine, University of California-Los Angeles, Los Angeles, CA 90095, USA
2. Department of Physiology, University of California-Los Angeles, Los Angeles, CA 90095, USA
3. Department of Orthopaedic Surgery, University of California-Los Angeles, Los Angeles, CA 90095, USA
4. Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA
5. Department of Bioengineering, University of California-Los Angeles, Los Angeles, CA 90095, USA
6. The David Geffen School of Medicine, University of California-Los Angeles, 10833 Le Conte Ave, Los Angeles, CA 90095, USA