Note the negative cells (arrows) that lie near a cell with positive expression.(b)Inner annulus cells in clusters in a Thompson Grade III disc. of the human intervertebral disc. Gene expression levels in human disc tissue were detectable for both MMP28 and the MMP28 precursor. MMP28 cytoplasmic localization was present in cells of the outer annulus; it was also present in some, but not all, cells of the inner annulus and nucleus. MMP28 was not found in the ECM of healthier Grade I to II discs, but was identified in the ECM of 61% of the more degenerated Grade III to V discs (P= 0.0018). There was a significant difference in cellular MMP28 distribution in the disc (P= 0.008): the outer annulus showed the largest percentage of cells positive for MMP28 immunolocalization, followed by the inner annulus and then the nucleus. Herniated discs showed a significantly greater CHK1-IN-2 proportion of MMP28-positive cells compared with nonherniated discs (P= 0.034). == Conclusions == Findings presented here show the first documentation of intervertebral disc expression and production of MMP28. MMP28 was found in both disc cell cytoplasm and in the ECM of more degenerated specimens, with greater cellular localization in the outer annulus and in herniated disc specimens. These findings are important because of the key role of MMPs in disc turnover and homeostasis, TLR1 and previous indications of a role for this MMP in matrix repair and matrix turnover in other tissues. Our data, which show the presence of MMP28 in human disc tissue, suggest that MMP28 may have a potentially important role in ECM modulation in the healthy and degenerating disc. == Introduction == The regulation and elevation in expression of the catabolic matrix metalloproteinases (MMPs) is usually of high importance in the human intervertebral disc since upregulation of these matrix-degrading enzymes results in matrix destruction associated with disc degeneration [1]. Historically, research has focused upon MMP1, MMP2, MMP3, MMP7, MMP8, MMP9, MMP13 and, more recently, MMP19 and MMP10 [2-12]. In the present study, we switched our attention to MMP28 (epilysin), the newest member of the MMP family, discovered in 2001 by Lohi and colleagues [13] and also by Marchenko and Strongin [14]. Related to our intervertebral disc interests, we were especially interested to find data reporting that this induction of MMP28 requires epidermal injury, suggesting a role for MMP28 in extracellular matrix (ECM) homeostasis [15]. Wound healing studies showed that MMP28 was spatially and temporally regulated. Recent work by Ren and colleagues has shown that mechanical compression can act to modulate wound healing and also to modulate expression of MMP28 [16]. Mechanical compression significantly upregulated MMP28 CHK1-IN-2 secretion in hypertrophic scars [16]. The closest relative of MMP28 at the amino acid sequence level is usually MMP19 (which has recently been identified in the human intervertebral disc [11]). MMP28 is usually a 59 kDa protein, first identified in keratinocytes and testis, and expressed at lower levels in the lung, heart, colon, intestine, bone, kidney, brain and other tissues [13,17]. MMP28 has catalytic activity as an endopeptidase and has the ability to degrade casein [13], and to date this nonspecific substrate for many proteases [18] is the only protein substrate reported for MMP28. The MMP28 protein requires divalent cations for activity, and was shown to be inhibited by a synthetic MMP inhibitor. MMP28 does not include domains characteristic of other MMP subfamilies (the disintegrin and thrombospondin-like regions found in a disintegrin and metalloproteinase and in a disintegrin and metalloproteinase with thrombospondin) or the transmembrane group as found CHK1-IN-2 in membrane-type MMPs [13], and the MMP28 promotor has a unique conserved GF-box that is required for basal expression in keratinocytes [19]. Recent work by Werner and colleagues has shown that MMP28 is usually upregulated during conditions of demyelation, suggesting anotherin vivorole for MMP28 [20]. In the work reported in the present article, we investigated whether MMP28 was expressed in the human intervertebral disc. Our objectives were to determine whether MMP28 and its precursor are expressedin vivoin human disc tissue, and to assess the location of MMP28 in disc tissue using immunohistochemistry. == Materials and methods == == Clinical study populace == Experimental study of disc specimens was approved prospectively by the authors’ Human Subjects Institutional Review Board. Since disc surgeries are routinely performed in.
Oxidative Phosphorylation