Mesenchymal Stem Cells Expressing Insulin-like Growth Factor-I (MSCIGF) Promote Fracture Healing and Restore New Bone Formation in Irs1 Knockout Mice: Analyses of MSCIGF Autocrine and Paracrine Regenerative Effects

Abstract

Failures of fracture repair (non-unions) occur in 10% of all fractures. The use of mesenchymal stem cells (MSC) in tissue regeneration appears to be rationale, safe and feasible. The contributions of MSC to the reparative process can occur through autocrine as well as paracrine effects. The primary objective of this study is to find a novel mean, by transplanting primary cultures of bone marrow-derived MSC expressing insulin-like growth factor-I (MSCIGF), to promote these seed-and-soil actions of MSC to fully implement their regenerative abilities in fracture repair and non-unions. MSCIGF or traceable MSCIGF-Lac-Z were transplanted into wild-type or insulin-receptor-substrate knock-out (Irs1−/−) mice with a stabilized tibia fracture. Healing was assed using biomechanical testing, micro-computed-tomography (µCT) and histological analyses. We found that systemically transplanted MSCIGF through autocrine and paracrine actions improved the fracture mechanical strength and increased new bone content while accelerating mineralization. We determined that IGF-I adapted the response of transplanted MSCIGF to promote their differentiation into osteoblasts. In vitro and in vivo studies showed that IGF-I-induced induced osteoglastogenesis in MSC was dependent of an intact IRS1-PI3K signaling. Furthermore, using Irs1−/− mice as a non-union fracture model through altered IGF signaling, we demonstrated that the autocrine effect of IGF-I on MSC restored the fracture new bone formation and promoted the occurrence of a well-organized callus that bridged the gap; a callus that basically absent in Irs1−/− left untransplanted or transplanted with MSC. We provided evidence of effects and mechanisms for transplanted MSCIGF in fracture repair and potentially to treat non-unions.

The Key Regulatory Roles of the PI3K/Akt Signaling Pathway in the Functionalities of Mesenchymal Stem Cells and Applications in Tissue Regeneration

“…interleukin-6 and TNF-alpha can synergistically costimulate MSCs to produce VEGF via the PI3K/Akt pathway. 106 NF-kB, a downstream protein in the PI3K/Akt pathway, was also shown to play an important role in the TNF-alphainduced production of VEGF, FGF, HGF, and IGF-1.…”

The epigenome of AML stem and progenitor cells

“…Among the observed pathways were "ephrin receptor signaling" for K4 (P10 and P7-9) and "hepatic fibrosis/hepatic stellate cell activation signaling" for K27 (P10, P11, and P7-9), implying common regulatory mechanisms at a pathway level to orchestrate differentiation from stem to progenitor cells. Both of these signaling pathways are also known to function in neural and intestinal stem cells, [37][38][39] implying common features of stem cells between different tissues, and even different conditions, that is, normal and tumor. When factoring in the most differentiated cells in P10, we found pathways related to the function of differentiated myeloid cells, suggesting the importance of histone modifications for further terminal differentiation.…”

Mesenchymal Stem Cell-Derived Exosomes Promote Fracture Healing in a Mouse Model

“…Transplantation of stem cells, such as bonemarrow-derived mesenchymal stem cells (MSCs), promotes tissue regeneration, including fracture healing [3][4][5]. Many studies indicate that transplanted MSCs contribute to tissue regeneration by mechanisms other than differentiation and direct tissue integration [6][7][8][9].…”