Date of Award
9-17-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Intervertebral disc (IVD) degeneration significantly contributes to disability and the economic burden of musculoskeletal diseases. Early changes in IVD degeneration include reduced cellularity and altered phenotype in nucleus pulposus (NP) cells, leading to diminished capacity for extracellular matrix (ECM) and glycosaminoglycan production. Cell supplementation, particularly with bone marrow-derived human mesenchymal stem cells (MSCs), has been explored to promote ECM synthesis and repair. MSCs offer potential for either direct cell replacement or by secreting factors to support disc repair by restoring biosynthetic activity of remaining endogenous NP cells and ameliorating inflammation. Biomaterials have been extensively studied to preserve and restore the healthy phenotype of IVD cells and to serve as cell carriers to protect and localize transplanted cells from the harsh environment of degenerative IVDs. Previous research demonstrated that integrin or syndecan binding peptides from laminin can induce degenerative primary human NP cells to re-express a juvenile, healthy phenotype. Prior work has also suggested that hydrogels presenting cell adhesive peptides can enhance not just primary cell survival, but MSC survival and pro-reparative functions. Additionally, growth factors such as Insulin-like growth factor 1 (IGF-1), play a multifaceted role in stem cell biology and may promote proliferation, survival, migration, and immunomodulation for MSCs. Biomaterial cell carriers can be functionalized with not just cell adhesive peptides, but peptides mimicking growth factors such as IGF-1 to enhance MSC functions while promoting cell retention and minimizing off-target effects seen with direct administration of soluble growth factors. This dissertation investigates two alternative types of peptide mimetics in combination with integrin-binding peptides to modulate the fate of primary human IVD cells and MSCs. In the first part, bio-orthogonal chemistries were used to conjugate syndecan and integrin-binding peptides to alginate to regulate NP cell adhesion and fate in 2D and 3D. While alginate is the default carrier for in vitro NP cell culture, “naked” alginate lacks functional ECM-derived ligands that are necessary to support cell survival and promote biosynthesis. Results show that this combination of syndecan and integrin binding peptides are superior to integrin or syndecan binding peptides alone in inducing a healthy, juvenile phenotype and biosynthesis in degenerative primary human NP cells. In the second part, IGF-1 peptide mimetics and cRGD peptides were functionalized onto alginate hydrogels to enhance MSC therapeutic potential. One IGF-1 peptide mimetic, which lacks homology to full-length IGF-1, is shown to activate the PI3K/Akt signaling pathway, support MSC survival, and reduce inflammatory cytokine production in MSCs challenged with interleukin-1 beta (IL-1β). Co-culture studies further demonstrate that MSCs within alginate hydrogels grafted with IGF-1 and cRGD peptides significantly reduced inflammation in primary NP cells. The work presented here illustrates the value of incorporating cell-adhesive peptides to promote cell viability, biosynthetic activity, and juvenile NP- specific phenotypes. These findings build upon previous research that cell-adhesive laminin motifs presented to NP cells support expression of specific phenotypes. The results also highlight the potential of growth factor peptide mimetics tethered to hydrogels to enhance the survival, reparative functions, and anti-inflammatory capabilities of transplanted cells to the disc. These insights enable rational design of hydrogels used as a carrier for cell-transplantation based therapies for IVD degeneration and inflammatory diseases.
Language
English (en)
Chair
Nathaniel Huebsch
Committee Members
Audrey McAlinden; Farshid Guilak; Jianjun Guan; Lori Setton