Regional variations in certain cellular characteristics in human lumbar intervertebral discs, including the presence of alpha-smooth muscle actin

An evaluation of the regional variation of certain cellular features in the human intervertebral disc (IVD) could lead to a better understanding of si te-specific properties relative to degradation, response to injury, and hea ling processes. The objective of this study was to determine how cell densi ty, cell morphology, cell grouping, and expression of a specific actin isof orm varied with location and degeneration in the human disc. A total of 41 human L4-L5 and L5-S1 discs removed postmortem from 21 individuals were ana lyzed. The discs were graded for degeneration based on the Thompson scale a nd processed for evaluation. Microtomed sections from paraffin-embedded spe cimens were stained with hematoxylin and eosin or a monoclonal antibody to alpha -smooth muscle actin (alpha -SMA), an actin isoform often associated with contraction., significant regional dependence was found for most of th e measured parameters. A fourfold increase in cell density was found in pro ceeding from the nucleus pulposus (NP) to the outer annulus (OA) of the IVD . Approximately 30% of the cells in the NP were present in groups. Virtuall y all of the cells in the NP and 40% of those in the OA were round. Moreove r, notable percentages (12-15%) of the cells in the NP and inner annulus (T A) contained alpha -SMA. Only pair density was found to be correlated with Thompson grade, with more degenerated specimens having higher values. A gre ater effect was also observed on the percentage of cells in groups. These f indings provide the basis for future work to investigate the importance of cells in groups, the role of alpha -SMA in the disc, and the changes in the se cellular characteristics in pathological disc conditions. (C) 2001 Ortho paedic Research Society. Published by Elsevier Science Ltd. All rights rese rved.