Mesenchymal stem cells express c-kit

Histological functions of parathyroid hormone on bone formation and bone blood vessels

BACKGROUND

The intermittent administration of parathyroid hormone (PTH) has been prescribed to osteoporotic patients due to its bone anabolic effects. In addition to its actions on bone cells, PTH appears to affect bone-specific blood vessels. These blood vessels are derived from bone marrow sinusoids, which express EphB4, a hallmark of veinous vascular endothelial cells. Given the presence of osteo-vascular interactions, it is important to elucidate the effects of PTH on bone cells and blood vessels in murine models.

HIGHLIGHTS

PTH stimulates preosteoblastic proliferation and osteoblastic bone formation. The former appears to be directly affected by PTH, whereas the latter requires osteoclast-mediated coupling. The administration of PTH through high-frequency dosage schemes accelerates bone turnover featuring remodeling-based bone formation, whereas low-frequency schemes cause mainly remodeling-based and partly modeling-based bone formation. Normally, many blood vessels lack alpha smooth muscle actin (αSMA)-immunoreactive vascular muscle cells surrounding basement membranes, indicating them being capillaries. However, PTH administration increases the number of blood vessels surrounded by αSMA-positive cells. These αSMA-positive cells spread out of blood vessels and express alkaline phosphatase and c-kit, suggesting their potential to differentiate into osteogenic and vascular endothelial/perivascular cells. Unlike bone cells, αSMA-positive cells did not appear in the periphery of blood vessels in the kidney and liver, and the thickness of the tunica media did not change regardless of PTH administration.

CONCLUSION

Based on the results of the study and presence of osseous-vascular interactions, PTH appears to influence not only osteoblastic cells, but also blood vessels in bone.

Intermittent PTH Administration Increases Bone-Specific Blood Vessels and Surrounding Stromal Cells in Murine Long Bones

To verify whether PTH acts on bone-specific blood vessels and on cells surrounding these blood vessels, 6-week-old male mice were subjected to vehicle (control group) or hPTH [1-34] (20 µg/kg/day, PTH group) injections for 2 weeks. Femoral metaphyses were used for histochemical and immunohistochemical studies. In control metaphyses, endomucin-positive blood vessels were abundant, but αSMA-reactive blood vessels were scarce. In the PTH-administered mice, the lumen of endomucin-positive blood vessels was markedly enlarged. Moreover, many αSMA-positive cells were evident near the blood vessels, and seemed to derive from those vessels. These αSMA-positive cells neighboring the blood vessels showed features of mesenchymal stromal cells, such as immunopositivity for c-kit and tissue nonspecific alkaline phosphatase (TNALP). Thus, PTH administration increased the population of perivascular/stromal cells positive for αSMA and c-kit, which were likely committed to the osteoblastic lineage. To understand the cellular events that led to increased numbers and size of bone-specific blood vessels, we performed immunohistochemical studies for PTH/PTHrP receptor and VEGF. After PTH administration, PTH/PTHrP receptor, VEGF and its receptor flk-1 were consistently identified in both osteoblasts and blood vessels (endothelial cells and surrounding perivascular cells). Our findings suggest that exogenous PTH increases the number and size of bone-specific blood vessels while fostering perivascular/stromal cells positive for αSMA/TNALP/c-kit.

Morphological and immunohistochemical phenotype of TCs in the intestinal bulb of Grass carp and their potential role in intestinal immunity

The current study investigated telocytes (TCs) in the intestinal bulb of Grass carp using light microscopy (LM), Transmission electron microscopy (TEM), scanning electron microscopy, and immunohistochemistry (IHC). By LM, TCs were distinguished by the typical morphological features that had a cell body and telopodes using HE, toluidine blue, methylene blue, Marsland silver stain, Grimelius's silver nitrate, Giemsa, PAS, combined AB pH2,5/PAS, Crossmon's and Mallory triple trichrome, Van Gieson stains, Verhoeff's stain, Sudan black, osmic acid, performic acid with methylene blue and bromophenol blue. TCs were identified under the epithelium as an individual cell or formed a TCs sheath. They detected in the lamina propria, between muscle fibers, around the myenteric plexus and fibrous tissue. TCs acquired immunological features of endocrine cells that exhibited high affinity for silver stain, performic acid with methylene blue, Marsland stain, and immunohistochemical staining using chromogranin A. Sub epithelial TCs were closely related to the endocrine cells. TCs and their secretory activities were recognized using acridine orange. TCs were identified by IHC using CD34, CD117, S100-protein, desmin. TCs formed a3D network that established contact with macrophage, mast cells, dendritic cells, lymphocytes, smooth muscle fibers, fibroblast, Schwann cells and nerve fibers. In conclusion, the localization of TCs in relation to different types of immune cells indicated their potential role in the maintenance of intestinal immunity.

C-KIT Expression Distinguishes Fetal from Postnatal Skeletal Progenitors

Hematopoietic stem cells (HSCs) and skeletal stem cells (SSCs) cohabit in the bone marrow. KITL (C-KIT ligand) from LEPR⁺ adult bone marrow stromal cells is pivotal for HSC maintenance. In contrast, it remains unclear whether KITL/C-KIT signaling also regulates SSCs. Here, we lineage traced C-KIT⁺ cells and found that C-KIT was expressed by fetal, but not postnatal skeletal progenitors. Fetal C-KIT⁺ cells gave rise to 20% of LEPR⁺ stromal cells in adult bone marrow, forming nearly half of all osteoblasts. Disruption of mTOR signaling in fetal C-KIT⁺ cells impaired bone formation. Notably, conditional deletion of Kitl from PRX1⁺ fetal bone marrow stromal cells, but not LEPR⁺ adult bone marrow stromal cells, significantly increased bone formation. Thus, our work identified C-KIT⁺ skeletal progenitors as an important source of bones formed during development.

The roles of telocytes in lung development and angiogenesis: An immunohistochemical, ultrastructural, scanning electron microscopy and morphometrical study

Many studies have been carried out to investigate the occurrence and distribution of telocytes (TCs) in many organs. However, their morphological development is still unclear. This study was performed to demonstrate the morphological development of TCs in rabbits' lung from fetal to postnatal life using light-, electron- microscopy, immunohistochemistry, morphometrical and statistical analysis. During the fetal life, these cells formed an extensive network of telopodes (Tps) which were in close contact with developing alveoli, bronchioles, stem cells and many other interstitial components. In addition, the TCs' number was significantly increased around the neocapillaries in fetal lung. In the fetal life, TCs were stellate in shape and characterized by large cell bodies and many short Tps that contained abundant rER, mitochondria, and ribosomes. By gradual increasing of ages, TCs were spindle in shape with two Tps contained a massive amount of secretory structures (exosomes, ectosomes, and multivesicular bodies). Moreover, TCs in postnatal lung showed a significant decrease in number and diameter of their cell bodies and a significant increase in the length of Tps compared with those in fetal life. The TCs contributed with pneumocytes and endothelium in the formation of air-blood barrier. The TCs' immunohistochemical profiles for CD34, vimentin, c-kit, connexin 43, vascular endothelial growth factor (VEGF), and neuron- specific enolase (NSE) differed between ages during the lung development. This study provided an evidence that TCs contributed to angiogenesis, the formation of the air-blood barrier, lung organization, and development.