Metabolomic Profiling and Mechanotransduction of Single Chondrocytes Encapsulated in Alginate Microgels

Jacob P Fredrikson,Ronald K June,Connie B Chang,Priyanka P Brahmachary,Ayten E Erdoğan,James N Wilking,Zachary K Archambault

doi:10.3390/cells11050900

Abstract

Articular cartilage is comprised of two main components, the extracellular matrix (ECM) and the pericellular matrix (PCM). The PCM helps to protect chondrocytes in the cartilage from mechanical loads, but in patients with osteoarthritis, the PCM is weakened, resulting in increased chondrocyte stress. As chondrocytes are responsible for matrix synthesis and maintenance, it is important to understand how mechanical loads affect the cellular responses of chondrocytes. Many studies have examined chondrocyte responses to in vitro mechanical loading by embedding chondrocytes in 3-D hydrogels. However, these experiments are mostly performed in the absence of PCM, which may obscure important responses to mechanotransduction. Here, drop-based microfluidics is used to culture single chondrocytes in alginate microgels for cell-directed PCM synthesis that closely mimics the in vivo microenvironment. Chondrocytes formed PCM over 10 days in these single-cell 3-D microenvironments. Mechanotransduction studies were performed, in which single-cell microgels mimicking the cartilage PCM were embedded in high-stiffness agarose. After physiological dynamic compression in a custom-built bioreactor, microgels exhibited distinct metabolomic profiles from both uncompressed and monolayer controls. These results demonstrate the potential of single cell encapsulation in alginate microgels to advance cartilage tissue engineering and basic chondrocyte mechanobiology.

Highlights

Osteoarthritis (OA) is the most common degenerative joint disease, which affects over 300 million people worldwide [1]
Microgel-encapsulated chondrocytes have up-regulated pathways related to amino acid synthesis and central energy metabolism
Previous studies investigated the effects of alginate macrogels on the formation of the pericellular matrix (PCM), but, while these macrogels support the formation of PCM, they have insufficient stiffness to mimic the in vivo elastic modulus surrounding chondrocytes, which is between 25 and 200 kPa [13–15]

Summary

Introduction

Osteoarthritis (OA) is the most common degenerative joint disease, which affects over 300 million people worldwide [1]. The articular cartilage, the soft loadbearing tissue that lines the interfaces of joints, begins to deteriorate [2]. This is associated with pain and loss of joint function. The tissue in human articular cartilage is spatially homogeneous, including the extracellular matrix (ECM), the territorial matrix, and the pericellular matrix (PCM). The cartilage is primarily comprised of ECM, a hydrated matrix of collagen and proteoglycans [2]. The PCM, which is primarily comprised of type-VI collagen and closely encapsulates the chondrocytes, like a cocoon, directly applies stimuli for chondrocyte mechanotransduction [3]. Cartilage experiences mechanical loads that vary in frequency and amplitude from activities such as walking, running, and jumping [4]. The PCM protects the chondrocytes from these mechanical loads, but in patients with OA, the PCM is weakened, resulting in increased chondrocyte stress [5]

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