Adipogenic Differentiation of hMSCs is Mediated by Recruitment of IGF-1r Onto the Primary Cilium Associated With Cilia Elongation

Abstract

Primary cilia are single non‐motile organelles that provide a highly regulated compartment into which specific proteins are trafficked as a critical part of various signaling pathways. The absence of primary cilia has been shown to prevent differentiation of human mesenchymal stem cells (hMSCs). Changes in primary cilia length are crucial for regulating signaling events; however it is not known how alterations in cilia structure relate to differentiation. This study tested the hypothesis that changes in primary cilia structure are required for stem cell differentiation. hMSCs expressed primary cilia that were labeled with acetylated alpha tubulin and visualized by confocal microscopy. Chemically induced differentiation resulted in lineage specific changes in cilia length and prevalence which were independent of cell cycle. In particular, adipogenic differentiation resulted in cilia elongation associated with the presence of dexamethasone, while insulin had an inhibitory effect on cilia length. Over a 7‐day time course, adipogenic differentiation media resulted in cilia elongation within 2 days followed by increased nuclear PPARγ levels; an early marker of adipogenesis. Cilia elongation was associated with increased trafficking of insulin‐like growth factor‐1 receptor β (IGF‐1Rβ) into the cilium. This was reversed on inhibition of elongation by IFT‐88 siRNA transfection, which also decreased nuclear PPARγ. This is the first study to show that adipogenic differentiation requires primary cilia elongation associated with the recruitment of IGF‐1Rβ onto the cilium. This study may lead to the development of cilia‐targeted therapies for controlling adipogenic differentiation and associated conditions such as obesity. Stem Cells 2015;33:1952–1961

Topography of calcium phosphate ceramics regulates primary cilia length and TGF receptor recruitment associated with osteogenesis

“…Recent findings show that cytoskeletal modulation by substrate topography affects primary cilia structure thereby regulating Wnt signalling in hBMSCs [20]. Furthermore primary cilia have been shown to be required for hBMSC osteogenic differentiation [21] and to undergo cilia elongation during osteogenesis as confirmed in the present study (Fig.3C) [26], [41]. These previous studies prompted the question as to whether the osteoinductive properties of TCP-S ceramics are associated with changes in primary cilia structure and function resulting from the alterations in cell morphology.…”

Adenylate Cyclase Type III Is Not a Ubiquitous Marker for All Primary Cilia during Development

“…A third hypothesis may be proposed; obesity in AC3 -/- mice and protection against obesity in mice with an AC3 gain of function mutation have been attributed to the primary cilium of hypothalamic neurons [23, 27]. Although mature adipocytes do not have a primary cilium, a primary cilium is observed in preadipocytes [28, 29, 30] (the embryos we observed had no identifiable preadipocytes); thus, one cannot exclude that AC3 present in mesenchymal cells cilium could be involved in adipocyte differentiation and resistance to diet-induced obesity.…”

Primary Cilia and Coordination of Receptor Tyrosine Kinase (RTK) and Transforming Growth Factor β (TGF-β) Signaling

“…Similarly, in human mesenchymal stem cells (hMSCs), adipogenic differentiation was shown to involve cilia elongation and recruitment of IGF-1Rb onto cilia (Fig. 2D), which was accompanied by increased nuclear accumulation of the early adipogenesis marker PPARg (Dalbay et al 2015). Interestingly, downstream transmission of ciliary IGF-1R signaling appears to rely on formation of a signaling platform at the ciliary base, composed of a complex of HSP90a, IRS-1, and AKT ( Fig.…”