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The article informs that osteoarthritis (OA) is a degenerative disorder and a major cause of pain and disability worldwide. For long time it has been considered a cartilage disease and currently it is best recognized as a whole joint disease whose pathogenesis is not fully understood. Study evidence shows that age affects the infrapatellar pad tissue causing a variation in extracellular matrix proteins' content and specific cells' morphometry.

The article offers information on role of piezo 1/2 mechanosensors in the infrapatellar fat pad-synovial membrane anatomo-functional unit. Topics include information on microscopic distribution of osteoarthritis pain-implied receptors; a fibro-adipose tissue of the knee; and mechanisms triggering and perpetuating the onset/progression of osteoarthritis (OA) disease.

Human meniscus plays a crucial role for knee load transmission and distribution, shock absorption, joint stability, lubrication and congruity [1], while cartilage is a smooth tissue that promotes the sliding of the articular strands. The aim of this work is to compare healthy (control) and pathological articular structures. We have analyzed samples of meniscus and articular cartilage obtained from 3 multiorgan donors (median age, 66 years), 5 patients with traumatic meniscal tear (median age, 41years) and 3 patient undergoing total knee replacement for osteoarthritis (OA) (median age, 72 years). In the different conditions we evaluated the ECM component (collagen fiber organization and proteoglycan presence), the appearance and distribution of calcification areas, and the modifications of the cellular structure. Ultrastructural analysis of control menisci and cartilage show rare condensed chromatin masses in diffuse chromatin and well preserved organelles. Both in trauma and in OA, increasing chromatin condensation, organelle degeneration and cytoplasmic vacuolization appear [2]. In pathological conditions, particularly in OA, autophagic vacuoles, which probably represent a cellular self-protection mechanism, also appear. The most evident ultrastructural changes have been observed when surgery takes place long time after trauma. In this case a high chromatin condensation, a large cytoplasmic vacuolization with degeneration of organelles and several necrotic cells can be observed. Calcification areas occur both in traumatic and osteoarthritic menisci and cartilage. In particular, specimens from traumatic menisci have a structure similar to osteoarthritic ones, especially if trauma occurs in a more adult subject. In both disorganization of collagen fibers, replaced with proteoglycans, appears. A reduction of collagen fibers sizes can be also observed, if compared to control condition. We can conclude that trauma might induces an increasing meniscal and cartilage degeneration, comparable to physiological aging. In all experimental conditions, in particular in traumatic meniscal tear, we observed apoptotic-like features. Traumatic and degenerative meniscal lesions have peculiar anatomic features and different proposed etiologies, yet both are associated with development or OA progression. [ABSTRACT FROM AUTHOR]

The extrasynovial adipose tissue Infrapatellar Fat Pad (IFP) is an emerging player in knee osteoarthritis (OA) [1,2]. While the role of constitutive adipocytes in secreting cytokines is known, little awareness on origin/function of the stem cells component exists. This study aims to isolate/characterize IFP-derived stem cells (IFP-dSCs) from OA patients investigating their role in disease development. IFP samples were processed to discard matrix and the adipocyte fraction. The resulting pellet was resuspended in proliferative medium and cultured routinely. IFP-dSCs morphology and ultrastructure were observed by optical microscope and Transmission Electron Microscope (TEM); expansion potential of cells was assessed by a population doubling level assay. IFP-dSCs vitality was assessed using a Apoptotic/Necrotic/Healthy Cells Detection Kit, while the metabolic activity of cell cultures was analysed by MTT assay. Flow cytometry analysis was performed to identify the presence of specific markers; in particular, IFP-dSCs were stained with antibodies against CD73/105/90/44/34/106, IL-6R/1R, VEGFR2. At last, IFP-dSCs plasticity was also assessed, evaluating their commitment towards the adipogenic, chondrogenic and endothelial lineages. IFP-dSCs isolation required 14 h; cells were fibroblast-like and typically spindle shaped at low density, showing a greater polygonal nucleus at high density. Semithin-sections stained with toluidine blue revealed vesicles in the cytoplasm, as confirmed by TEM analysis. These rounded formations of electrondense material were in proximity of empty round vesicles and in some contact areas a partial fusion between the external membranes was appreciable. An exponential growth during the entire long-term expansion period was observed, with a replication time of 42.7 ± 3.8 h. From passage (P)8 to P20, cells performed 11.9 ± 0.9 population doublings. IFP-dSCs immunophenotype was positive for the investigated markers, suggesting a role in modulation of inflammation; interestingly, cells were 100% CD73+bright both at low and high P in colture. Preliminary data about plasticity revealed the ability in differentiating towards adipogenic and endothelial lineages. Further analysis will be required to assess chondrogenic commitment. Experimental evidence on IFP-dSCs seem to correlate histopathological features of IFP in OA (i.e. thickening of interlobular septa, increase in vascularization and innervation) with the stem cell component. [ABSTRACT FROM AUTHOR]

The suprapatellar fat pad (SFP) is located above the patella and behind the suprapatellar joint recess with the function of increasing the congruency of the extensor mechanism. Osteoarthritis SFP has been demonstrated to produce high amount of inflammatory molecules and to be more fibrous than subcutaneous adipose tissue in osteoarthritis (OA) patients. The aim of this study was to analyze 1. the morphological characteristics of the SFP compared to that of the infrapatellar fat pad (IFP) in normal subjects; 2. the magnetic resonance (MR) volumetric characteristics of the IFP and the SFP in non-OA controls compared to moderate and endstage OA patients. Five specimens of SFP were sampled from bodies of the donation program of the University of Padova without history of OA. The SFP consisted of white adipose tissue, of lobular type, with lobules delimited by thin connective septa. Forty-four MR images were collected: a) 17 control; b) 15 patients with moderate OA ; and c) 12 patients with end-stage OA. Volume, depth, femoral and tibial arch lengths of IFP were quantified. The SFP volume, oblique, antero-posterior and, cranio-caudal lengths were determined. A decrease of IFP volume, depth, femoral, and tibial arch lengths in moderate and end-stage OA compared to controls were observed. A difference in IFP hypointense signal was found between groups. No differences were found in SFP characteristics between the groups. In controls and moderate OA patients, correlations were found among the different MRI characteristics of both IFP and SFP, while in the end-stage OA group correlations were found only in SFP. Differences of the IFP MRI morphometric characteristics between the groups analyzed supports an important role of IFP in OA pathology and progression. On the contrary, no differences were highlighted in SFP analysis suggesting that this fat pad is not clearly involved in OA, probably due to its peculiar localization and different function. [ABSTRACT FROM AUTHOR]