Introduction: Osteoarthritis (OA) is one of the most common causes of knee pain, and the most common form of
arthritis. It causes pain and disability, and there is currently no cure. Recent research in knee OA highlights the
role of the meniscus in OA pathology. In this thesis, the overall aim was to study the proteome and microstructure
of the human meniscus, both in healthy subjects and OA patients, in order to increase our knowledge about the
human meniscus and the processes that occur during degeneration and OA.
Design: In the first part of this thesis, posterior horns of medial and lateral menisci from deceased donors and OA
patients were analysed with histology and micro-computed tomography (μCT), in order to compare the
microstructure of healthy and OA menisci (paper I). In the second, and major part of this thesis, human menisci
were analysed with mass spectrometry (MS)-based proteomics. First, meniscus body samples and articular
cartilage samples from deceased donors were compared using two different MS-based methods – dataindependent
acquisition (DIA) and data-dependent acquisition (DDA) (paper II). Next, three zones (peripheral,
middle and inner zone) of the body of the medial meniscus from deceased donors were compared using DIA
(paper III). Lastly, meniscal plugs from the same meniscal posterior horns that had been used in paper I, were
analysed with DIA.
Results: In paper I, we found that higher histopathological scores were associated with more degeneration, and
that medial menisci from OA patients had the highest degree of degeneration. We also observed that the degree
of degeneration varied between the different sections of the meniscus. In paper II, we showed that the majority of
the proteins were similar between articular cartilage and meniscus, but that there were nonetheless some
proteomic differences. Furthermore, we found that DIA identified more differentially expressed proteins, with less
missing values. In paper III, we observed that many proteins were common to all zones of the meniscus, and that
the majority of meniscal proteins were associated with ECM organisation. The largest zonal differences were
between the peripheral and inner zones. In paper IV, where we compared menisci from OA patients and deceased
donors, we showed that the largest differences could be seen between the medial menisci from the two groups,
and that there was an increase of proteoglycans and proteins such as MMP3 and TIMP1.
Conclusions: Due to the many advantages of DIA, we considered it superior to DDA and used it in subsequent
MS analyses. Although articular cartilage and meniscus had similar proteomic compositions, we detected several
differences by MS. We also detected large differences between the peripheral and inner zones of the healthy
meniscus body, probably related to the higher degree of cellularity and vascularisation in the peripheral zone. On
the other hand, the middle and inner zones of the meniscus contained more extracellular proteins and therefore
appeared to be more similar to articular cartilage. Comparison of healthy and OA menisci revealed increased
degeneration of the OA menisci, with more disorganised collagen networks and the presence of cysts and
calcifications. The OA menisci also had an increase of proteins such as MMP3 and TIMP1, which suggests
simultaneous activation of both catabolic and anabolic processes. The increased degeneration in OA menisci
suggests a strong association between OA and meniscal degeneration.