Abstract
BackgroundCurrent tissue engineering methods are insufficient for total joint resurfacing, and chondrocytes undergo de-differentiation when expanded on tissue culture plastic. De-differentiated chondrocytes show poor re-differentiation in culture, giving reduced glycosaminoglycan (GAG) and collagen matrix accumulation. To address this, porcine synoviocyte-derived extracellular matrix and low (5%) oxygen tension were assessed for their ability to enhance human articular chondrocyte expansion and maintain re-differentiation potential.MethodsPorcine synoviocyte matrices were devitalized using 3 non-detergent methods. These devitalized synoviocyte matrices were compared against tissue culture plastic for their ability to support human chondrocyte expansion. Expansion was further compared at both low (5%), and atmospheric (20%) oxygen tension on all surfaces. Expanded cells then underwent chondrogenic re-differentiation in aggregate culture at both low and atmospheric oxygen tension. Aggregates were assessed for their GAG and collagen content both biochemically and histologically.ResultsHuman chondrocytes expanded twice as fast on devitalized synoviocyte matrix vs. tissue culture plastic, and cells retained their re-differentiation capacity for twice the number of population doublings. There was no significant difference in growth rate between low and atmospheric oxygen tension. There was significantly less collagen type I, collagen type II, aggrecan and more MMP13 expression in cells expanded on synoviocyte matrix vs. tissue culture plastic. There were also significant effects due to oxygen tension on gene expression, wherein there was greater collagen type I, collagen type II, SOX9 and less MMP13 expression on tissue culture plastic compared to synoviocyte matrix. There was a significant increase in GAG, but not collagen, accumulation in chondrocyte aggregates re-differentiated at low oxygen tension over that achieved in atmospheric oxygen conditions.ConclusionsSynoviocyte-derived matrix supports enhanced expansion of human chondrocytes such that the chondrocytes are maintained in a state from which they can re-differentiate into a cartilage phenotype after significantly more population doublings. Also, low oxygen tension supports GAG, but not collagen, accumulation. These findings are a step towards the production of a more functional, tissue engineered cartilage.
Highlights
Human articular cartilage has long been known to have a poor repair capacity [1]
Synoviocyte-derived matrix supports enhanced expansion of human chondrocytes such that the chondrocytes are maintained in a state from which they can re-differentiate into a cartilage phenotype after significantly more population doublings
We found significantly enhanced growth of human chondrocytes on all synoviocyte matrixcoated flasks compared to cells on tissue culture (TC) plastic alone at both atmospheric (20%) O2 (Fig 2A) and low (5%) O2 (Fig 2B) conditions, regardless of the method used to devitalize the matrix
Summary
Human articular cartilage has long been known to have a poor repair capacity [1]. Cartilage consists of a largely avascular, hypocellular, collagen and glycosaminoglycan (GAG) matrix [2]. Microfracture and mosaicplasty have the advantage of being performed in a single surgery, but are only applicable to small lesions, and microfracture often results in a fibrous repair [5] Both ACI and MACI are autologous cell transplantation techniques, which have the disadvantage of requiring two surgical procedures; cartilage biopsies are taken from low load-bearing regions, grown in culture and implanted. In an objective assessment of chondrogenesis, biopsies of 406 ACI patients showed hyaline cartilage in only 14.9% of patients, mixed hyaline and fibrous cartilage in 27.5%, fibrocartilage in 47.7% and fibrous repair in the remaining 9.9% [8]; similar results have been reported elsewhere [9] This lack of hyaline cartilage formation could be due to the limited ability of human chondrocytes to expand on tissue culture (TC) plastic and their progressive loss of chondrogenic phenotype [10,11,12] and decreased capacity to re-differentiate [13].
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