Primary cilia-dependent signaling is involved in regulating mesenchymal stem cell proliferation and pluripotency maintenance.J Mol Histol. 2020;51:241-250. [PMID: 32399704 DOI: 10.1007/s10735-020-09876-7]

Aberrant Wnt/β-catenin signaling in the mesenchymal stem cells of LZTFL1-depleted mice leads to increased adipogenesis, with implications for obesity

Obesity is one of the main clinical characteristics associated with the heterogeneous genetic disorder Bardet-Biedl syndrome (BBS). Leucine zipper transcription factor like 1 (LZTFL1) is a member of the BBS gene family. Our work showed that Lztfl1knockout (LZKO) mice display the obesity phenotype as early as 3 months of age. Mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into various cell types, including adipocytes. To understand the role of LZTFL1 in adipogenesis, we analyzed MSCs isolated from LZKO mouse compact bones (CB-MSCs). Compared to wildtype (WT), LZKO CB-MSCs had elongated primary cilia with tapered tips and increased levels of peroxisome proliferator-activated receptor γ (PPARγ), a key transcription factor that favors adipogenesis, and nuclear glucocorticoid receptor (GR), a transcription factor involved in Pparg activation. Also, LZKO CB-MSCs had a lower level of total β-catenin, a core factor of the antiadipogenic canonical Wnt/b-catenin signaling pathway involved in limiting the nuclear localization of GR. Interaction between caveolin1 (CAV1) and LRP6, the main receptor for canonical Wnt signaling, is known to be critical for Wnt pathway activation and β-catenin stabilization. Compared to WT cells, LZKO cells had elevated total, cell-surface, and lipid-raft-associated LRP6 and reduced CAV1, strongly indicating alterations in the components of the Wnt-signaling pathway. We show that in the absence of LZTFL1, adipogenesis-restraining Wnt/β-catenin signaling is inhibited, and adipogenesis-favorable factors are stimulated in CB-MSCs, leading to enhanced adipogenesis. Evidence provided here could help in understanding the mechanism and molecular basis of obesity in LZTFL1-defective patients.

Primary cilia-associated signalling in squamous cell carcinoma of head and neck region

Squamous cell carcinoma (SCC) of the head and neck originates from the mucosal lining of the upper aerodigestive tract, including the lip, tongue, nasopharynx, oropharynx, larynx and hypopharynx. In this review, we summarise what is currently known about the potential function of primary cilia in the pathogenesis of this disease. As primary cilia represent a key cellular structure for signal transduction and are related to cell proliferation, an understanding of their role in carcinogenesis is necessary for the design of new treatment approaches. Here, we introduce cilia-related signalling in head and neck squamous cell carcinoma (HNSCC) and its possible association with HNSCC tumorigenesis. From this point of view, PDGF, EGF, Wnt and Hh signalling are discussed as all these pathways were found to be dysregulated in HNSCC. Moreover, we review the clinical potential of small molecules affecting primary cilia signalling to target squamous cell carcinoma of the head and neck area.

Mechanobiology and Primary Cilium in the Pathophysiology of Bone Marrow Myeloproliferative Diseases

Philadelphia-Negative Myeloproliferative neoplasms (MPNs) are a diverse group of blood cancers leading to excessive production of mature blood cells. These chronic diseases, including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), can significantly impact patient quality of life and are still incurable in the vast majority of the cases. This review examines the mechanobiology within a bone marrow niche, emphasizing the role of mechanical cues and the primary cilium in the pathophysiology of MPNs. It discusses the influence of extracellular matrix components, cell-cell and cell-matrix interactions, and mechanosensitive structures on hematopoietic stem cell (HSC) behavior and disease progression. Additionally, the potential implications of the primary cilium as a chemo- and mechanosensory organelle in bone marrow cells are explored, highlighting its involvement in signaling pathways crucial for hematopoietic regulation. This review proposes future research directions to better understand the dysregulated bone marrow niche in MPNs and to identify novel therapeutic targets.

Role of ciliopathy protein TMEM107 in eye development: insights from a mouse model and retinal organoid

Primary cilia are cellular surface projections enriched in receptors and signaling molecules, acting as signaling hubs that respond to stimuli. Malfunctions in primary cilia have been linked to human diseases, including retinopathies and ocular defects. Here, we focus on TMEM107, a protein localized to the transition zone of primary cilia. TMEM107 mutations were found in patients with Joubert and Meckel-Gruber syndromes. A mouse model lacking Tmem107 exhibited eye defects such as anophthalmia and microphthalmia, affecting retina differentiation. Tmem107 expression during prenatal mouse development correlated with phenotype occurrence, with enhanced expression in differentiating retina and optic stalk. TMEM107 deficiency in retinal organoids resulted in the loss of primary cilia, down-regulation of retina-specific genes, and cyst formation. Knocking out TMEM107 in human ARPE-19 cells prevented primary cilia formation and impaired response to Smoothened agonist treatment because of ectopic activation of the SHH pathway. Our data suggest TMEM107 plays a crucial role in early vertebrate eye development and ciliogenesis in the differentiating retina.

Trans differentiating human adipose-derived mesenchymal stem cells into male germ-like cells utilizing Rabbit Sertoli cells: An experimental study

Background

Mesenchymal stem cells (MSCs) are deemed as potential new therapeutic agents for infertility treatment and adipose tissue (AT) becomes a potential MSCs source. To direct MSCs through the differentiation process properly, an environment comparable to the in vivo niche might be indispensable.

Objective

This study aims to differentiate human AT-derived MScs (hAD-MScs) into male germ-like cells in vitro using a combination of rabbit Sertoli cells conditioned medium (SCCM), bone morphogenetic protein 4, and retinoic acid.

Materials and Methods

MScs were isolated from human ATs of fertile and infertile donors. The verified MScs were differentiated using a 2-step protocol; the first step included 20 ng/ml bone morphogenetic protein 4 treatment. The second step was performed utilizing 1 μM retinoic acid and/or SCCM. The morphological changes and the expression of germ cell (GC)-specific markers: octamer-binding transcription factor-4; stimulated by retinoic-acid-8, synaptonemal complex protein-3, andprotamine-1 were assessed in the treated cells using quantitative polymerase chain reaction.

Results

Induction of hAD-MScs resulted in the upregulation of GC-specific genes where SCCM treatment showed the highest expression. The synaptonemal complex protein-3andprotamine-1 gene expression was detected after 19 and 26 days of induction, respectively. PRM1 was detected in hAD-MScs cultured in SCCM earlier than in other treated groups. The treated cells became more elongated-like spindles and formed aggregates.

Conclusion

hAD-MScs differentiated to GC lineage exhibited the ability to express GC-specific markers under in vitro conditions, and rabbit's Sertoli cells can be used for inducing transdifferentiation of hAD-MScs into germ-like cells.

Primary cilia-associated protein IFT172 in ciliopathies

Cilium is a highly conserved antenna-like structure protruding from the surface of the cell membrane, which is widely distributed on most mammalian cells. Two types of cilia have been described so far which include motile cilia and immotile cilia and the latter are also known as primary cilia. Dysfunctional primary cilia are commonly associated with a variety of congenital diseases called ciliopathies with multifaceted presentations such as retinopathy, congenital kidney disease, intellectual disability, cancer, polycystic kidney, obesity, Bardet Biedl syndrome (BBS), etc. Intraflagellar transport (IFT) is a bi-directional transportation process that helps maintain a balanced flow of proteins or signaling molecules essential for the communication between cilia and cytoplasm. Disrupted IFT contributes to the abnormal structure or function of cilia and frequently promotes the occurrence of ciliopathies. Intraflagellar transport 172 (IFT172) is a newly identified member of IFT proteins closely involved in some rare ciliopathies such as Mainzer-Saldino syndrome (MZSDS) and BBS, though the underpinning causal mechanisms remain largely elusive. In this review, we summarize the key findings on the genetic and protein characteristic of IFT172, as well as its function in intraflagellar transport, to provide comprehensive insights to understand IFT172-related ciliopathies.

Primary Cilia: A Cellular Regulator of Articular Cartilage Degeneration

Osteoarthritis (OA) is the most common joint disease that can cause pain and disability in adults. The main pathological characteristic of OA is cartilage degeneration, which is caused by chondrocyte apoptosis, cartilage matrix degradation, and inflammatory factor destruction. The current treatment for patients with OA focuses on delaying its progression, such as oral anti-inflammatory analgesics or injection of sodium gluconate into the joint cavity. Primary cilia are an important structure involved in cellular signal transduction. Thus, they are very sensitive to mechanical and physicochemical stimuli. It is reported that the primary cilia may play an important role in the development of OA. Here, we review the correlation between the morphology (location, length, incidence, and orientation) of chondrocyte primary cilia and OA and summarize the relevant signaling pathways in chondrocytes that could regulate the OA process through primary cilia, including Hedgehog, Wnt, and inflammation-related signaling pathways. These data provide new ideas for OA treatment.

Stem cells' centrosomes: How can organelles identified 130 years ago contribute to the future of regenerative medicine?

At the core of regenerative medicine lies the expectation of repair or replacement of damaged tissues or whole organs. Donor scarcity and transplant rejection are major obstacles, and exactly the obstacles that stem cell-based therapy promises to overcome. These therapies demand a comprehensive understanding of the asymmetric division of stem cells, i.e. their ability to produce cells with identical potency or differentiated cells. It is believed that with better understanding, researchers will be able to direct stem cell differentiation. Here, we describe extraordinary advances in manipulating stem cell fate that show that we need to focus on the centrosome and the centrosome-derived primary cilium. This belief comes from the fact that this organelle is the vehicle that coordinates the asymmetric division of stem cells. This is supported by studies that report the significant role of the centrosome/cilium in orchestrating signaling pathways that dictate stem cell fate. We anticipate that there is sufficient evidence to place this organelle at the center of efforts that will shape the future of regenerative medicine.

Phenotypic, morphological, and metabolic characterization of vascular-spheres from human vascular mesenchymal stem cells

The ability to form spheroids under non‐adherent conditions is a well‐known property of human mesenchymal stem cells (hMSCs), in addition to stemness and multilineage differentiation features. In the present study, we tested the ability of hMSCs isolated from the vascular wall (hVW‐MSCs) to grow as spheres, and provide a characterization of this 3D model. hVW‐MSCs were isolated from femoral arteries through enzymatic digestion. Spheres were obtained using ultra‐low attachment and hanging drop methods. Immunophenotype and pluripotent genes (SOX‐2, OCT‐4, NANOG) were analyzed by immunocytochemistry and real‐time PCR, respectively. Spheres histological and ultrastructural architecture were examined. Cell viability and proliferative capacity were measured using LIVE/DEATH assay and ki‐67 proliferation marker. Metabolomic profile was obtained with liquid chromatography–mass spectrometry. In 2D, hVW‐MSCs were spindle‐shaped, expressed mesenchymal antigens, and displayed mesengenic potential. 3D cultures of hVW‐MSCs were CD44⁺, CD105^low, CD90^low, exhibited a low propensity to enter the cell cycle as indicated by low percentage of ki‐67 expression and accumulated intermediate metabolites pointing to slowed metabolism. The 3D model of hVW‐MSCs exhibits stemness, dormancy and slow metabolism, typically observed in stem cell niches. This culture strategy can represent an accurate model to investigate hMSCs features for future clinical applications in the vascular field.

Primary Cilium Is Involved in Stem Cell Differentiation and Renewal through the Regulation of Multiple Signaling Pathways

Signaling networks guide stem cells during their lineage specification and terminal differentiation. Primary cilium, an antenna-like protrusion, directly or indirectly plays a significant role in this guidance. All stem cells characterized so far have primary cilia. They serve as entry- or check-points for various signaling events by controlling the signal transduction and stability. Thus, defects in the primary cilia formation or dynamics cause developmental and health problems, including but not limited to obesity, cardiovascular and renal anomalies, hearing and vision loss, and even cancers. In this review, we focus on the recent findings of how primary cilium controls various signaling pathways during stem cell differentiation and identify potential gaps in the field for future research.