Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
Osteoarthritis Cartilage. 2010 Jan;18(1):126-37. doi: 10.1016/j.joca.2009.08.005. Epub 2009 Sep 1.
Mechanical loading of cell-laden synthetic hydrogels is one strategy for regenerating functional cartilage. This work tests the hypothesis that type of loading (continuous vs intermittent) and timing when loading is applied (immediate vs delayed) influence anabolic and catabolic activities of chondrocytes when encapsulated in poly(ethylene glycol) (PEG) hydrogels.
Primary bovine chondrocytes encapsulated in PEG hydrogels were subjected to unconfined dynamic compressive strains applied continuously or intermittently for 1 week (i.e., immediate) or intermittently for 1 week but after a 1 week free-swelling (FS) period (i.e., delayed). Anabolic activities were assessed by gene expression for collagen II and aggrecan (AGC) and extracellular matrix (ECM) deposition by (immuno)histochemistry. Catabolic activities were assessed by gene expression for matrix metalloproteinases, MMP-1, 3, and 13.
Intermittent loading (IL) upregulated ECM and MMP expressions, e.g., 2-fold, 16-fold and 8-fold for collagen II, MMP-1, MMP-3, respectively. Continuous loading upregulated AGC expression 1.5-fold but down-regulated MMP-1 (3-fold) and -3 (2-fold) expressions. For delayed loading, chondrocytes responded to FS conditions by down-regulating MMP expressions (P<0.01), but were less sensitive to loading when applied during week 2. Spatially, deposition of ECM molecules was dependent on the timing of loading, where immediate loading favored enhanced collagen II deposition.
The type and timing of dynamic loading dramatically influenced ECM and MMP gene expression and to a lesser degree matrix deposition. Our findings suggest that early applications of IL is necessary to stimulate both anabolic and catabolic activities, which may be important in regenerating and restructuring the engineered tissue long-term.
细胞负载合成水凝胶的机械加载是再生功能性软骨的一种策略。本研究检验了以下假设：加载类型（连续与间歇）和加载时机（即时与延迟）会影响包埋在聚乙二醇（PEG）水凝胶中的软骨细胞的合成代谢和分解代谢活性。
将原代牛软骨细胞包埋在 PEG 水凝胶中，然后施加持续或间歇的无约束动态压缩应变 1 周（即时）或间歇 1 周，但在 1 周自由膨胀（FS）期后（延迟）施加。通过基因表达评估合成代谢活性，评估指标为 II 型胶原和聚集蛋白聚糖（AGC）的基因表达，通过（免疫）组织化学评估细胞外基质（ECM）沉积。通过基因表达评估分解代谢活性，评估指标为基质金属蛋白酶 MMP-1、3 和 13。
间歇加载（IL）上调 ECM 和 MMP 表达，例如，II 型胶原、MMP-1 和 MMP-3 的表达分别上调 2 倍、16 倍和 8 倍。连续加载上调 AGC 表达 1.5 倍，但下调 MMP-1（3 倍）和 MMP-3（2 倍）表达。对于延迟加载，软骨细胞对 FS 条件的反应是下调 MMP 表达（P<0.01），但在第 2 周施加时对加载的敏感性降低。空间上，ECM 分子的沉积依赖于加载的时机，即时加载有利于增强 II 型胶原的沉积。
动态加载的类型和时机显著影响 ECM 和 MMP 基因表达，对基质沉积的影响较小。我们的研究结果表明，早期应用 IL 是刺激合成代谢和分解代谢活性所必需的，这对于长期再生和重构工程组织可能很重要。
