Relevance of meniscal cell regional phenotype to tissue engineering

<b><i>Purpose</i>:</b> Meniscus contains heterogeneous populations of cells that have not been fully characterized. Cell phenotype is often lost during culture; however, culture expansion is typically required for tissue engineering. We examined and compared cell-surface molecule expression levels on human meniscus cells from the vascular and avascular regions and articular chondrocytes while documenting changes during culture-induced dedifferentiation. <b><i>Materials and Methods</i>:</b> Expressions of 16 different surface molecules were examined by flow cytometry after monolayer culture for 24 h, 1 week, and 2 weeks. Menisci were also immunostained to document the spatial distributions of selected surface molecules. <b><i>Results</i>:</b> Meniscus cells and chondrocytes exhibited several similarities in surface molecule profiles with dynamic changes during culture. A greater percentage of meniscal cells were positive for CD14, CD26, CD49c, and CD49f compared to articular chondrocytes. Initially, more meniscal cells from the vascular region were positive for CD90 compared to cells from the avascular region or chondrocytes. Cells from the vascular region also expressed higher levels of CD166 and CD271 compared to cells from the avascular region. CD90, CD166, and CD271-positive cells were predominately perivascular in location. However, CD166-positive cells were also located in the superficial layer and in the adjacent synovial and adipose tissue. <b><i>Conclusions</i>:</b> These surface marker profiles provide a target phenotype for differentiation of progenitors in tissue engineering. The spatial location of progenitor cells in meniscus is consistent with higher regenerative capacity of the vascular region, while the surface progenitor subpopulations have potential to be utilized in tears created in the avascular region.

**目的**：半月板（meniscus）内含有尚未被完全鉴定的异质性细胞群。细胞表型在体外培养过程中常会发生丢失，但组织工程通常需要进行细胞培养扩增。本研究对来自血管区与无血管区的人半月板细胞及关节软骨细胞（articular chondrocytes）的细胞表面分子表达水平进行了检测与对比，并记录了培养诱导的去分化（dedifferentiation）过程中的分子表达变化。
**材料与方法**：本研究采用流式细胞术（flow cytometry）检测了单层培养24小时、1周及2周后16种不同表面分子的表达情况；同时还对半月板组织进行了免疫染色，以明确选定表面分子的空间分布特征。
**结果**：半月板细胞与软骨细胞的表面分子谱存在多处共性，且其表达水平在培养过程中呈现动态变化。相较于关节软骨细胞，表达CD14、CD26、CD49c及CD49f的半月板细胞占比更高。培养初始阶段，血管区来源的半月板细胞中CD90阳性细胞占比高于无血管区来源的细胞或软骨细胞。血管区来源的细胞相较于无血管区来源的细胞，其CD166与CD271的表达水平也更高。CD90、CD166及CD271阳性细胞主要定位于血管周围区域，但CD166阳性细胞同时也分布于组织表层以及邻近的滑膜与脂肪组织中。
**结论**：上述表面标志物谱可为组织工程中祖细胞（progenitor cells）的定向分化提供目标表型。半月板内祖细胞的空间分布特征与血管区更高的再生能力相符，同时通过表面标志物筛选得到的祖细胞亚群，有望用于修复无血管区出现的半月板撕裂损伤。