Effects of Exogenous IGF-1 Delivery on the Early Expression of IGF-1 Signaling Molecules by Alginate Embedded Chondrocytes

Abstract

Cartilage tissue engineering remains a significant challenge for both researchers and clinicians. Many strategic approaches, such as the delivery of growth factors to an in vitro cultured cartilage construct, continue to receive significant attention. However, the effects of delivering exogenous signaling molecules on endogenous signaling pathways within an engineered tissue are not well understood. In order to address this concern, we have investigated how the delivery of insulin-like growth factor-1 (IGF-1, delivered at concentrations of 0, 10, 50, and 100 ng/mL) affects the endogenous expression of IGF-1, its receptor (IGF-1R), and a well known IGF-1 binding protein (IGFBP-3) by articular chondrocytes embedded in alginate hydrogels over 8 days. To the best of our knowledge, this is the first report of delivery effects upon endogenous signal expression in a three-dimensional system relevant to tissue engineering objectives. Results showed significant differences in mRNA expression of IGF-1, IGF-1R, type II collagen, and type I collagen by day 8 between the induced versus noninduced IGF-1 groups. At day 8, the induced IGF-1 groups expressed IGF-1 mRNA four times lower than the 0 ng/mL IGF-1 group. Further, the IGF-1R mRNA expression was five times higher for the groups exposed to exogenous IGF-1 versus the 0 ng/mL IGF-1 case. Interestingly, the expression of IGFBP-3 decreased for all groups. Type II collagen expression was the highest and type I collagen was the lowest for the IGF-1 delivered samples. Finally, the different concentrations of IGF-1 investigated did not demonstrate significantly different trends in mRNA expression levels. Overall, results indicate that exogenous IGF-1 delivery does affect signaling molecule expression by chondrocytes embedded in alginate hydrogels, particularly downregulating the delivered signal while upregulating its receptor.

Benefits of Recombinant Adeno-Associated Virus (rAAV)-Mediated Insulinlike Growth Factor I (IGF-I) Overexpression for the Long-Term Reconstruction of Human Osteoarthritic Cartilage by Modulation of the IGF-I Axis

“…Of note, we also observed that IGF-I overexpression in OA cartilage in situ was capable of significantly decreasing the expression of IGFBP3 and IGFBP4, two inhibitors of the IGF-I actions (40)(41)(42), while increasing the levels of two of its potentiators (IGFBP5 and its own receptor [IGF-IR]) (42,43), an effect noted at prolonged time points and probably the result of the steady levels of IGF-I production from the rAAV transgene sequence. In this regard, the effects of IGF-I on these components of the IGF-I axis via rAAV in OA cartilage are in good agreement with previous findings when providing IGF-I as a recombinant molecule to articular chondrocytes in vitro (73)(74)(75)(76). Also noteworthy, the elevated, sustained levels of IGF-I produced in OA cartilage via rAAV might have been capable of counteracting the wellknown effects of pathogenic adipokines on the destruction of articular cartilage (3,4).…”

Stimulation of Chondrogenic Differentiation of Mesenchymal Stem Cells

“…Study on the same model showed that the combined use of chondrocytes and IGF-1 not only formed collagen type II rich matrix, but also enhanced the overall continuity and consistency of the repaired tissues (1). IGF-1 and its receptor are expressed by chondrocytes, and they are the essential mediator of homeostasis in cartilage, promoting viability and proliferation of chondrocytes (24). With collagen type II matrix, cartilage defects filled with IGF-1 can be repaired more efficiently (25).…”

Matrix molecule influence on chondrocyte phenotype and proteoglycan 4 expression by alginate‐embedded zonal chondrocytes and mesenchymal stem cells

“…[26][27][28] Briefly, alginate solution was prepared by mixing and heating alginic acid sodium salt from brown algae (Sigma-Aldrich, St. Louis, MO, molecular weight 80,000-120,000 Da, M:G ratio $1.56, viscosity !2,000 cP), 0.15 M sodium chloride (Sigma-Aldrich), and 0.025 M HEPES, sodium salt (J.T. Baker, Phillipsburg, NJ) into deionized water (pH 7.4), and then autoclaved for sterilization.…”