Sonic Hedgehog and Retinoic Acid Induce Bone Marrow-Derived Stem Cells to Differentiate into Glutamatergic Neural Cells

Repair of Peripheral Nerve Sensory Impairments via the Transplantation of Bone Marrow Neural Tissue-Committed Stem Cell-Derived Sensory Neurons

The present study aimed to investigate the efficacy of transplantation of bone marrow neural tissue-committed stem cell-derived sensory neuron-like cells for the repair of peripheral nerve sensory impairments in rats. Bone marrow was isolated and cultured to obtain the neural tissue-committed stem cells (NTCSCs), and the differentiation of these cells into sensory neuron-like cells was induced. Bone marrow mesenchymal stem cells (BMSCs), bone marrow NTCSCs, and bone marrow NTCSC-derived sensory neurons (NTCSC-SNs) were transplanted by microinjection into the L4 and L5 dorsal root ganglions (DRGs) in an animal model of sensory defect. On the 2nd, 4th, 8th, and 12th week after the transplantation, the effects of the three types of stem cells on the repair of the sensory functional defect were analyzed via behavioral observation, sensory function evaluation, electrophysiological examination of the sciatic nerve, and morphological observation of the DRGs. The results revealed that the transplanted BMSCs, NTCSCs, and NTCSC-SNs were all able to repair the sensory nerves. In addition, the effect of the NTCSC-SNs was significantly better than that of the other two types of stem cells. The general posture and gait of the animals in the sensory defect model exhibited evident improvement over time. Plantar temperature sensitivity and pain sensitivity gradually recovered, and the sensation latency was reduced, with faster sensory nerve conduction velocity. Transplantation of NTCSC-SNs can improve the repair of peripheral nerve sensory defects in rats.

ALDH as a Stem Cell Marker in Solid Tumors

Aldehyde dehydrogenase (ALDH) is an enzyme that participates in important cellular mechanisms as aldehyde detoxification and retinoic acid synthesis; moreover, ALDH activity is involved in drug resistance, a characteristic of cancer stem cells (CSCs). Even though ALDH is found in stem cells, CSCs and progenitor cells, this enzyme has been successfully used to identify and isolate cell populations with CSC properties from several tumor origins. ALDH is allegedly involved in cell differentiation through its product, retinoic acid. However, direct or indirect ALDH inhibition, using specific inhibitors or retinoic acid, has shown a reduction in ALDH activity, along with the loss of stem cell traits, reduction of cell proliferation, invasion, and drug sensitization. For these reasons, ALDH and retinoic acid are promising therapeutic targets. This review summarizes the current evidence for ALDH as a CSCs marker in solid tumors, as well as current knowledge about the functional roles of ALDH in CSCs. We discuss the controversy of ALDH activity to maintain CSC stemness, or conversely, to promote cell differentiation. Finally, we review the advances in using ALDH inhibitors as anti-cancer drugs.

Distinct retinoic acid receptor (RAR) isotypes control differentiation of embryonal carcinoma cells to dopaminergic or striatopallidal medium spiny neurons

Embryonal carcinoma (EC) cells are pluripotent stem cells extensively used for studies of cell differentiation. Although retinoic acid (RA) is a powerful inducer of neurogenesis in EC cells, it is not clear what specific neuronal subtypes are generated and whether different RAR isotypes may contribute to such neuronal diversification. Here we show that RA treatment during EC embryoid body formation is a highly robust protocol for generation of striatal-like GABAergic neurons which display molecular characteristics of striatopallidal medium spiny neurons (MSNs), including expression of functional dopamine D2 receptor. By using RARα, β and γ selective agonists we show that RARγ is the functionally dominant RAR in mediating RA control of early molecular determinants of MSNs leading to formation of striatopallidal-like neurons. In contrast, activation of RARα is less efficient in generation of this class of neurons, but is essential for differentiation of functional dopaminergic neurons, which may correspond to a subpopulation of inhibitory dopaminergic neurons expressing glutamic acid decarboxylase in vivo.

New Insights Into the Roles of Retinoic Acid Signaling in Nervous System Development and the Establishment of Neurotransmitter Systems

Secreted chiefly from the underlying mesoderm, the morphogen retinoic acid (RA) is well known to contribute to the specification, patterning, and differentiation of neural progenitors in the developing vertebrate nervous system. Furthermore, RA influences the subtype identity and neurotransmitter phenotype of subsets of maturing neurons, although relatively little is known about how these functions are mediated. This review provides a comprehensive overview of the roles played by RA signaling during the formation of the central and peripheral nervous systems of vertebrates and highlights its effects on the differentiation of several neurotransmitter systems. In addition, the evolutionary history of the RA signaling system is discussed, revealing both conserved properties and alternate modes of RA action. It is proposed that comparative approaches should be employed systematically to expand our knowledge of the context-dependent cellular mechanisms controlled by the multifunctional signaling molecule RA.

Fate of graft cells: what should be clarified for development of mesenchymal stem cell therapy for ischemic stroke?

Mesenchymal stem cells (MSCs) are believed to be promising for cell administration therapy after ischemic stroke. Because of their advantageous characteristics, such as ability of differentiation into neurovascular lineages, avoidance of immunological problems, and abundance of graft cells in mesodermal tissues, studies regarding MSC therapy have increased recently. However, several controversies are yet to be resolved before a worldwide consensus regarding a standard protocol is obtained. In particular, the neuroprotective effects, the rate of cell migration to the lesion, and differentiation direction differ depending on preclinical observations. Analyses of these differences and application of recent developments in stem cell biology or engineering in imaging modality may contribute to identification of criteria for optimal stem cell therapy in which reliable protocols, which control cell quality and include safe administration procedures, are defined for each recovery phase after cerebral ischemia. In this mini review, we examine controversies regarding the fate of grafts and the prospects for advanced therapy that could be obtained through recent developments in stem cell research as direct conversion to neural cells.