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Unfolding of membrane ruffles of in situ chondrocytes under compressive loads
Author(s) -
Moo Eng Kuan,
Herzog Walter
Publication year - 2017
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.23260
Subject(s) - chondrocyte , cartilage , membrane , materials science , biophysics , chemistry , biomedical engineering , extracellular matrix , compression (physics) , anatomy , composite material , biology , biochemistry , medicine
Impact loading results in chondrocyte death. Previous studies implicated high tensile strain rates in chondrocyte membranes as the cause of impact‐induced cell deaths. However, this hypothesis relies on the untested assumption that chondrocyte membranes unfold in vivo during physiological tissue compression, but do not unfold during impact loading. Although membrane unfolding has been observed in isolated chondrocytes during osmotically induced swelling and mechanical compression, it is not known if membrane unfolding also occurs in chondrocytes embedded in their natural extracellular matrix. This study was aimed at quantifying changes in membrane morphology of in situ superficial zone chondrocytes during slow physiological cartilage compression. Bovine cartilage‐bone explants were loaded at 5 μm/s to nominal compressive strains ranging from 0% to 50%. After holding the final strains for 45 min, the loaded cartilage was chemically pre‐fixed for 12 h. The cartilage layer was post‐processed for visualization of cell ultrastructure using electron microscopy. The changes in membrane morphology in superficial zone cells were quantified from planar electron micrographs by measuring the roughness and the complexity of the cell surfaces. Qualitatively, the cell surface ruffles that existed before loading disappeared when cartilage was loaded. Quantitatively, the roughness and complexity of cell surfaces decreased with increasing load magnitudes, suggesting a load‐dependent use of membrane reservoirs. Chondrocyte membranes unfold in a load‐dependent manner when cartilage is compressed. Under physiologically meaningful loading conditions, the cells likely expand their surface through unfolding of the membrane ruffles, and therefore avoid direct stretch of the cell membrane. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:304–310, 2017.