Modulation of the gene expression of annulus fibrosus-derived stem cells using poly(ether carbonateurethane)urea scaffolds of tunable elasticity

Significance Statement

Annulus fibrosus (AF) injuries lead to substantial intervertebral disc deterioration which characterizes degenerative disc diseases. Repair of AF, however, remains challenging due to the tremendous heterogeneity of Annulus fibrosus tissue. Since the differentiation of stem cells significantly relies on the elasticity of substrate, a series of biodegradable poly(ether carbonate urethane)urea (PECUU) materials whose elasticity resembled that of native Annulus fibrosus tissue were synthesized in this study. When Annulus fibrosus-derived stem cells (AFSCs) were cultured on electrospun PECUU fibrous scaffolds, the gene expression and protein production of major matrix components, including collagen-I, collagen-II and aggrecan, and cell traction forces gradually changed with the elasticity of PECUU. Such substrate elasticity-dependent modulation of Annulus fibrosus-derived stem cells was similar to the gradual transition in the genetic, biochemical, and biomechanical characteristics of cells from inner to outer regions of native Annulus fibrosus tissue. This work has, for the first time, revealed that Annulus fibrosus-derived stem cells are able to present different gene expression patterns simply as a result of the elasticity of scaffold material. Findings from this study will help develop adequate materials for Annulus fibrosus regeneration.

About the author

Professor Bin Li is the director of the Biomaterials and Cell Mechanics Laboratory (BCML) of Orthopedic Institute at Soochow University, Suzhou, China. He received the bachelor degree in 1996 and PhD degree in Materials Science from Tsinghua University in 2001. He then joined the Institute of Materials Research and Engineering, Singapore as a Research Associate until 2004. After that he consecutively pursued research training at Carnegie Mellon University, University of Pittsburgh, and Harvard University until 2009, when he took the current position as a full professor at Soochow University. He is the recipient of the Orthopaedics Research Award (1st prize) from Chinese Orthopaedic Association, Xu Guangqi Program from the French Embassy in China, and France Talent Innovation from the Consulate General of France in Shanghai. He currently serves as the chair of China Development Committee of International Chinese Musculoskeletal Research Society (ICMRS). He is a fellow of Chinese Orthopaedic Research Society (CORS), Chinese Association of Orthopaedic Surgeons (CAOS), Chinese Association of Rehabilitation Medicine (CARM), and International Society of Orthopaedic Surgery and Traumatology (SICOT). He has delivered about 40 invited talks and is the author of over 70 publications and 9 book chapters. He now leads a multidisciplinary research group studying biomaterials for bone and cartilage repair, stem cells and tissue engineering, smart molecular recognition and controlled release, surface modification and functionalization, and cellular biomechanics and mechanobiology.

About the author

Dr. Caihong Zhu is a research associate and a member of the Biomaterials and Cell Mechanics Laboratory (BCML) of Orthopedic Institute at Soochow University. She received the bachelor degree in Polymer Chemistry from Nanjing University in 2001 and PhD degree in Polymer Chemistry from Soochow University in 2010. She joined Soochow University in 2012. Her research interests include biomaterials for bone and intervertebral disc regeneration and controlled drug delivery.

About the author

Dr. Jun Li is an orthopaedic surgeon who received his PhD degree at the Soochow University. Currently, he is a postdoctoral researcher at Shenzhen University. His major research interests include bone and cartilage regeneration via stem cell transplantation and osteoporosis.

Journal Reference

Acta Biomater. 2016;29:228-38.

Caihong Zhu, Jun Li, Chen Liu, Pinghui Zhou, Huilin Yang, Bin Li.

Department of Orthopaedics, The First Affiliated Hospital, Orthopaedic Institute, Soochow University, 188 Shizi St, Suzhou, Jiangsu 215006, China.

These authors contributed equally to this study. Email: [email protected]

Abstract

Annulus fibrosus (AF) injuries commonly lead to substantial deterioration of the intervertebral disc (IVD). While tissue engineering has recently evolved into a promising approach for AF regeneration, it remains challenging due to the cellular, biochemical, and mechanical heterogeneity of AF tissue. In this study, we explored the use of AF-derived stem cells (AFSCs) to achieve diversified differentiation of cells for AF tissue engineering. Since the differentiation of stem cells relies significantly on the elasticity of the substrate, we synthesized a series of biodegradable poly(ether carbonate urethane)urea (PECUU) materials whose elasticity approximated that of native AF tissue. When AFSCs were cultured on electrospun PECUU fibrous scaffolds, the gene expression of collagen-I in the cells increased with the elasticity of scaffold material, whereas the expression of collagen-II and aggrecan genes showed an opposite trend. At the protein level, the content of collagen-I gradually increased with substrate elasticity, while collagen-II and GAG contents decreased. In addition, the cell traction forces (CTFs) of AFSCs gradually decreased with scaffold elasticity. Such substrate elasticity-dependent changes of AFSCs were similar to the gradual transition in the genetic, biochemical, and biomechanical characteristics of cells from inner to outer regions of native AF tissue. Together, findings from this study indicate that AFSCs, depending on the substrate elasticity, have strong tendencies to differentiate into various types of AF-like cells, thereby providing a solid foundation for the tissue engineering applications of AFSCs.

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