IntroductionDegenerative joint diseases including osteoarthritis (OA) are common, particularly in the elderly. Early signs of OA include progressive loss from articular cartilage of the proteoglycan aggrecan, reflected by a loss of safranin O staining, excessive damage to type II collagen, and general degeneration and fibrillation of the cartilage surface, resulting ultimately in a loss of articular cartilage (1).One of the primary targets of this disease is type II collagen, the major structural collagen found in articular cartilage in healthy individuals. There is ordinarily a strict balance between the production of type II collagen and degradation of this protein by catabolic enzymes during normal remodeling of cartilage (1). Pathological conditions such as OA are characterized by a loss of this balance with increased proteolysis (1-5) and upregulation of the synthesis of type II procollagen (5) and aggrecan (6).Matrix metalloproteinases (MMPs) comprise a family of zinc-dependent enzymes that degrade extracellular matrix components. MMPs are synthesized in articulating joints by synovial cells and chondrocytes. In mature articular cartilage, chondrocytes maintain the cartilage-specific matrix phenotype. Elevated expression of MMPs is associated with cartilage degradation (1). MMP-13, also known as human collagenase-3, is thought to play an important role in type II collagen degradation in articular cartilage and especially in OA (4, 7-9). Type II collagen is the preferred substrate for MMP-13 (4, 7, 10). Expression and contents of MMP-1 (collagenase-1) and 11,12), expression of MMP-8 (collagenase-2), and collagenase activity (4,8) are upregulated in human OA cartilage.Spontaneous development of focal sites degeneration has been described in aging guinea pigs (13). Sublines of the inbred STR/ORT strain of mice also develop spontaneous OA with aging (14). Mice exhibit upregulated expression of MMP-13 and collagenase activity is upregulated in focal lesions (15). In guinea pigs, MMP-1 and MMP-13 are also upregulated in OA lesions associated with increased collagenase activity (16). It has been suggested that increased collagenase-3 (MMP-13) activity plays a pivotal role in the pathogenesis of osteoarthritis (OA). We have used tetracycline-regulated transcription in conjunction with a cartilage-specific promoter to target a constitutively active human MMP-13 to the hyaline cartilages and joints of transgenic mice. Postnatal expression of this transgene resulted in pathological changes in articular cartilage of the mouse joints similar to those observed in human OA. These included characteristic erosion of the articular cartilage associated with loss of proteoglycan and excessive cleavage of type II collagen by collagenase, as well as synovial hyperplasia. These results demonstrate that excessive MMP-13 activity can result in articular cartilage degradation and joint pathology of the kind observed in OA, suggesting that excessive activity of this proteinase can lead to this disease.

No abstract

No abstract

No abstract

The c-Jun N-terminal kinase (JNK) pathway potentially links together the three major pathological hallmarks of Alzheimer’s disease (AD): development of amyloid plaques, neurofibrillary tangles, and brain atrophy. As activation of the JNK pathway has been observed in amyloid models of AD in association with peri-plaque regions and neuritic dystrophy, as we confirm here for Tg2576/PSM146L transgenic mice, we directly tested whether JNK inhibition could provide neuroprotection in a novel brain slice model for amyloid precursor protein (APP)-induced neurodegeneration. We found that APP/amyloid β (Aβ)-induced neurodegeneration is blocked by both small molecule and peptide inhibitors of JNK, and provide evidence that this neuroprotection occurs downstream of APP/Aβ production and processing. Our findings demonstrate that Aβ can induce neurodegeneration, at least in part, through the JNK pathway and suggest that inhibition of JNK may be of therapeutic utility in the treatment of AD.