Primary Cilia as a Biomarker in Mesenchymal Stem Cells Senescence: Influencing Osteoblastic Differentiation Potency Associated with Hedgehog Signaling Regulation

Abstract

Bone tissue engineering-based therapy for bone lesions requires the expansion of seeding cells, such as autologous mesenchymal stem cells (MSCs). A major obstacle to this process is the loss of the phenotype and differentiation capacity of MSCs subjected to passage. Recent studies have suggested that primary cilia, primordial organelles that transduce multiple signals, particularly hedgehog signals, play a role in senescence. Therefore, we explored the relationships among senescence, primary cilia, and hedgehog signaling in MSCs. Ageing of MSCs by expansion in vitro was accompanied by increased cell doubling time. The osteogenic capacity of aged MSCs at passage 4 was compromised compared to that of primary cells. P4 MSCs exhibited reductions in the frequency and length of primary cilia associated with decreased intensity of Arl13b staining on cilia. Senescence also resulted in downregulation of the expression of hedgehog components and CDKN2A. Suppression of ciliogenesis reduced the gene expression of both Gli1, a key molecule in the hedgehog signaling pathway and ALP, a marker of osteoblastic differentiation. This study demonstrated that the senescence of MSCs induced the loss of osteoblastic differentiation potency and inactivated hedgehog signaling associated with attenuated ciliogenesis, indicating that primary cilia play a mediating role in and are biomarkers of MSC senescence; thus, future antisenescence strategies involving manipulation of primary cilia could be developed.

Aging Associates with Cilium Elongation and Dysfunction in Kidney and Pancreas

“…[47] Of note, regardless of whether cilia become shorter or longer in senescent cells, Hh signaling capacity is disturbed. [38,47] Additionally, if cells are not able to reabsorb the primary cilium, they fail to enter the cell cycle and can become senescent. [39] This may give certain cell types such as neural progenitors a longer time window for unwanted differentiation leading to a loss of these cells and consequently a reduced number of neurons.…”

“…As mentioned above, signaling cascades such as the Hh pathway are disturbed, if cilia length exceeds or is below its ideal for a given cell type. [17,38,47] Moreover, also motile cilia are impaired in their function if their length is not optimal. One such example is symmetry defects that can arise, if motile cilia are unable to efficiently propel fluids in the left-right organizer due to length abnormalities.…”

“…[38] Intriguingly, though, this may not be a universal response to senescence as cultured mesenchymal stem cells show shortened cilia, which seems to reduce stemness. [47] Of note, regardless of whether cilia become shorter or longer in senescent cells, Hh signaling capacity is disturbed. [38,47] Additionally, if cells are not able to reabsorb the primary cilium, they fail to enter the cell cycle and can become senescent.…”

Senescent cells: A therapeutic target for osteoporosis

“…73 After serial passage, MSCs have a reduced capacity to differentiate into osteogenic lineages and downregulate alkaline phosphatase (ALP), collagen type 1 (Col I), Runx2 and steric. [74][75][76][77] These MSCs upregulate adipogenesis CEBPα, CEBPβ, CEBPγ, and peroxisome proliferator-activated receptor (PPAR)γ. 78,79 This phenotype F I G U R E 1 Overview of bone marrow environment.…”

“…Mesenchymal stem cells (MSCs) also maintain haematopoietic stem cells (HSC) function 73 . After serial passage, MSCs have a reduced capacity to differentiate into osteogenic lineages and downregulate alkaline phosphatase (ALP), collagen type 1 (Col I), Runx2 and steric 74–77 . These MSCs upregulate adipogenesis CEBPα, CEBPβ, CEBPγ, and peroxisome proliferator‐activated receptor (PPAR)γ 78,79 .…”