S100A6 (calcyclin) is a novel marker of neural stem cells and astrocyte precursors in the subgranular zone of the adult mouse hippocampus

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

A New Approach for Exploring Reperfusion Brain Damage in Hypoxic Ischemic Encephalopathy

Reperfusion is an essential pathological stage in hypoxic ischemic encephalopathy (HIE). Although the Rice-Vannucci model is widely used in HIE research, it remains difficult to replicate HIE-related reperfusion brain injury. The purpose of this study is to establish a rat model of hypoxia ischemia reperfusion brain damage (HIRBD) using a common carotid artery (CCA) muscle bridge in order to investigate the mechanisms of cerebral resistance to hypoxic-ischemic and reperfusion brain damage. Random assignment of Sprague-Dawley (SD) rats to the Sham, HIRBD, and Rice-Vannucci groups. Changes in body weight, mortality rate, spontaneous alternation behavior test (SAB test), and dynamic changes in cerebral blood flow (CBF) were detected. The damaged cerebral cortices were extracted for morphological comparison, transcriptomic analysis, and quantitative real-time PCR. Harvesting the hippocampus for transmission electron microscopy (TEM) detection. As a result, CCA muscle bridge could effectively block CBF, which recovered after the muscle bridge detachment. Pathological comparison, the SAB test, and TEM analysis revealed that brain damage in Rice-Vannucci was more severe than HIRBD. Gpx1, S100a6, Cldn5, Esr1, and Gfap were highly expressed in both HIRBD and Rice-Vannucci. In conclusion, the CCA muscle bridge-established HIRBD model could be used as an innovative and dependable model to simulate pathological process of HIRBD.

Single-cell transcriptomic and neuropathologic analysis reveals dysregulation of the integrated stress response in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a sporadic neurodegenerative tauopathy variably affecting brainstem and cortical structures and characterized by tau inclusions in neurons and glia. The precise mechanism whereby these protein aggregates lead to cell death remains unclear. To investigate the contribution of these different cellular abnormalities to PSP pathogenesis, we performed single-nucleus RNA sequencing and analyzed 45,559 high quality nuclei targeting the subthalamic nucleus and adjacent structures from human post-mortem PSP brains with varying degrees of pathology compared to controls. Cell-type specific differential expression and pathway analysis identified both common and discrete changes in numerous pathways previously implicated in PSP and other neurodegenerative disorders. This included EIF2 signaling, an adaptive pathway activated in response to diverse stressors, which was the top activated pathway in vulnerable cell types. Using immunohistochemistry, we found that activated eIF2α was positively correlated with tau pathology burden in vulnerable brain regions. Multiplex immunofluorescence localized activated eIF2α positivity to hyperphosphorylated tau (p-tau) positive neurons and ALDH1L1-positive astrocytes, supporting the increased transcriptomic EIF2 activation observed in these vulnerable cell types. In conclusion, these data provide insights into cell-type-specific pathological changes in PSP and support the hypothesis that failure of adaptive stress pathways play a mechanistic role in the pathogenesis and progression of PSP.

S100A6: molecular function and biomarker role

S100A6 (also called calcyclin) is a Ca2+-binding protein that belongs to the S100 protein family. S100A6 has many functions related to the cytoskeleton, cell stress, proliferation, and differentiation. S100A6 also has many interacting proteins that are distributed in the cytoplasm, nucleus, cell membrane, and outside the cell. Almost all these proteins interact with S100A6 in a Ca2+-dependent manner, and some also have specific motifs responsible for binding to S100A6. The expression of S100A6 is regulated by several transcription factors (such as c-Myc, P53, NF-κB, USF, Nrf2, etc.). The expression level depends on the specific cell type and the transcription factors activated in specific physical and chemical environments, and is also related to histone acetylation, DNA methylation, and other epigenetic modifications. The differential expression of S100A6 in various diseases, and at different stages of those diseases, makes it a good biomarker for differential diagnosis and prognosis evaluation, as well as a potential therapeutic target. In this review, we mainly focus on the S100A6 ligand and its transcriptional regulation, molecular function (cytoskeleton, cell stress, cell differentiation), and role as a biomarker in human disease and stem cells.

The Role of S100A6 in Human Diseases: Molecular Mechanisms and Therapeutic Potential

S100A6, also known as calcyclin, is a low-molecular-weight Ca2+-binding protein from the S100 family that contains two EF-hands. S100A6 is expressed in a variety of mammalian cells and tissues. It is also expressed in lung, colorectal, pancreatic, and liver cancers, as well as other cancers such as melanoma. S100A6 has many molecular functions related to cell proliferation, the cell cycle, cell differentiation, and the cytoskeleton. It is not only involved in tumor invasion, proliferation, and migration, but also the pathogenesis of other non-neoplastic diseases. In this review, we focus on the molecular mechanisms and potential therapeutic targets of S100A6 in tumors, nervous system diseases, leukemia, endometriosis, cardiovascular disease, osteoarthritis, and other related diseases.

Nestin is a marker of unipotent embryonic and adult progenitors differentiating into an epithelial cell lineage of the hair follicles

Nestin is an intermediate filament protein transiently expressed in neural stem/progenitor cells. We previously demonstrated that outer root sheath (ORS) keratinocytes of adult hair follicles (HFs) in mice descend from nestin-expressing cells, despite being an epithelial cell lineage. This study determined the exact stage when nestin-expressing ORS stem/precursor cells or their descendants appear during HF morphogenesis, and whether they are present in adult HFs. Using Nes-Cre/CAG-CAT-EGFP mice, in which enhanced green fluorescent protein (EGFP) is expressed following Cre-based recombination driven by the nestin promoter, we found that EGFP⁺ cells appeared in the epithelial layer of embryonic HFs as early as the peg stage. EGFP⁺ cells in hair pegs were positive for keratin 14 (K14) and K5, but not vimentin, SOX2, SOX10, or S100 alpha 6. Tracing of tamoxifen-induced EGFP⁺ cells in postnatal Nes-CreERT2/CAG-CAT-EGFP mice revealed labeling of some isthmus HF epithelial cells in the first anagen stage. EGFP⁺ cells in adult HFs were not immunolabeled for K15, an HF multipotent stem cell marker. However, when hairs were depilated in Nes-CreERT2/CAG-CAT-EGFP mice to induce the anagen stage after tamoxifen injection, the majority of ORS keratinocytes in depilation-induced anagen HFs were labeled for EGFP. Our findings indicate that nestin-expressing unipotent progenitor cells capable of differentiating into ORS keratinocytes are present in HF primordia and adult HFs.

S100A6 as a Constituent and Potential Marker of Adult and Cancer Stem Cells

Adult or tissue stem cells are present in various tissues of the organism where they reside in a specific environment called the niche. Owing to their ability to generate a progeny that can proliferate and differentiate into specialized cell types, adult stem cells constitute a source of new cells necessary for tissue maintenance and/or regeneration. Under normal conditions they divide with a frequency matching the pace of tissue renewal but, following tissue damage, they can migrate to the site of injury and expand/divide intensively to facilitate tissue repair. For this reason much hope is being placed on the use of adult stem cells in regenerative therapies, including tissue engineering. Identification and characterization of tissue stem cells has been a laborious process due to their scarcity and lack of universal markers. Nonetheless, recent studies, employing various types of transcriptomic analyses, revealed some common trends in gene expression pattern among stem cells derived from different tissues, suggesting the importance of certain genes/proteins for the unique properties of these cells. S100A6, a small calcium binding protein, has been recognized as an important factor influencing cell proliferation and differentiation. Accumulating results show that S100A6 is a constituent of adult stem cells and, in some cases, may even be considered as their marker. Thus, in this review we summarize literature data concerning the presence of S100A6 in adult and cancer stem cells and speculate on its potential role and usefulness as a marker of these cells.

Molecular diversity of diencephalic astrocytes reveals adult astrogenesis regulated by Smad4

Astrocytes regulate brain‐wide functions and also show region‐specific differences, but little is known about how general and region‐specific functions are aligned at the single‐cell level. To explore this, we isolated adult mouse diencephalic astrocytes by ACSA‐2‐mediated magnetic‐activated cell sorting (MACS). Single‐cell RNA‐seq revealed 7 gene expression clusters of astrocytes, with 4 forming a supercluster. Within the supercluster, cells differed by gene expression related to ion homeostasis or metabolism, with the former sharing gene expression with other regions and the latter being restricted to specific regions. All clusters showed expression of proliferation‐related genes, and proliferation of diencephalic astrocytes was confirmed by immunostaining. Clonal analysis demonstrated low level of astrogenesis in the adult diencephalon, but not in cerebral cortex grey matter. This led to the identification of Smad4 as a key regulator of diencephalic astrocyte in vivo proliferation and in vitro neurosphere formation. Thus, astrocytes show diverse gene expression states related to distinct functions with some subsets being more widespread while others are more regionally restricted. However, all share low‐level proliferation revealing the novel concept of adult astrogenesis in the diencephalon.

Single-cell RNA sequencing reveals Nestin+ active neural stem cells outside the central canal after spinal cord injury

Neural stem cells (NSCs) in the spinal cord hold great potential for repair after spinal cord injury (SCI). The ependyma in the central canal (CC) region has been considered as the NSCs source in the spinal cord. However, the ependyma function as NSCs after SCI is still under debate. We used Nestin as a marker to isolate potential NSCs and their immediate progeny, and characterized the cells before and after SCI by single-cell RNA-sequencing (scRNA-seq). We identified two subgroups of NSCs: the subgroup located within the CC cannot prime to active NSCs after SCI, while the subgroup located outside the CC were activated and exhibited the active NSCs properties after SCI. We demonstrated the comprehensive dynamic transcriptome of NSCs from quiescent to active NSCs after SCI. This study reveals that Nestin⁺ cells outside CC were NSCs that activated upon SCI and may thus serve as endogenous NSCs for regenerative treatment of SCI in the future.

Defining the Adult Neural Stem Cell Niche Proteome Identifies Key Regulators of Adult Neurogenesis

The mammalian brain contains few niches for neural stem cells (NSCs) capable of generating new neurons, whereas other regions are primarily gliogenic. Here we leverage the spatial separation of the sub-ependymal zone NSC niche and the olfactory bulb, the region to which newly generated neurons from the sub-ependymal zone migrate and integrate, and present a comprehensive proteomic characterization of these regions in comparison to the cerebral cortex, which is not conducive to neurogenesis and integration of new neurons. We find differing compositions of regulatory extracellular matrix (ECM) components in the neurogenic niche. We further show that quiescent NSCs are the main source of their local ECM, including the multi-functional enzyme transglutaminase 2, which we show is crucial for neurogenesis. Atomic force microscopy corroborated indications from the proteomic analyses that neurogenic niches are significantly stiffer than non-neurogenic parenchyma. Together these findings provide a powerful resource for unraveling unique compositions of neurogenic niches.

Identification and Biochemical Characterization of High Mobility Group Protein 20A as a Novel Ca2+/S100A6 Target

During screening of protein-protein interactions, using human protein arrays carrying 19,676 recombinant glutathione s-transferase (GST)-fused human proteins, we identified the high-mobility protein group 20A (HMG20A) as a novel S100A6 binding partner. We confirmed the Ca²⁺-dependent interaction of HMG20A with S100A6 by the protein array method, biotinylated S100A6 overlay, and GST-pulldown assay in vitro and in transfected COS-7 cells. Co-immunoprecipitation of S100A6 with HMG20A from HeLa cells in a Ca²⁺-dependent manner revealed the physiological relevance of the S100A6/HMG20A interaction. In addition, HMG20A has the ability to interact with S100A1, S100A2, and S100B in a Ca²⁺-dependent manner, but not with S100A4, A11, A12, and calmodulin. S100A6 binding experiments using various HMG20A mutants revealed that Ca²⁺/S100A6 interacts with the C-terminal region (residues 311–342) of HMG20A with stoichiometric binding (HMG20A:S100A6 dimer = 1:1). This was confirmed by the fact that a GST-HMG20A mutant lacking the S100A6 binding region (residues 311–347, HMG20A-ΔC) failed to interact with endogenous S100A6 in transfected COS-7 cells, unlike wild-type HMG20A. Taken together, these results identify, for the first time, HMG20A as a target of Ca²⁺/S100 proteins, and may suggest a novel linkage between Ca²⁺/S100 protein signaling and HMG20A function, including in the regulation of neural differentiation.

Deciphering the Forebrain Disorder in a Chicken Model of Cerebral Hernia

Cerebral hernia in crested chicken has been characterized as the protrusion of cerebral hemispheres into the unsealed skull for hundreds of years, since Charles Darwin. The development of deformed forebrain (telencephalon) of cerebral hernia remains largely unknown. Here, the unsealed frontal skull combined with misplaced sphenoid bone was observed and potentially associated with brain protuberance. The shifted pallidum, elongated hippocampus, expanded mesopallium and nidopallium, and reduced hyperpallium were observed in seven regions of the malformed telencephalon. The neurons were detected with nuclear pyknosis and decreased density. Astrocytes showed uneven distribution and disordered protuberances in hyperpallium and hippocampus. Transcriptome analyses of chicken telencephalon (cerebral hernia vs. control) revealed 547 differentially expressed genes (DEGs), mainly related to nervous system development, and immune system processes, including astrocyte marker gene GFAP, and neuron and astrocyte developmental gene S100A6. The upregulation of GFAP and S100A6 genes in abnormal telencephalon was correlated with reduced DNA methylation levels in the promoter regions. The morphological, cellular, and molecular variations in the shape, regional specification, and cellular states of malformed telencephalon potentially participate in brain plasticity and previously reported behavior changes. Chickens with cerebral hernia might be an interesting and valuable disease model to further explore the recognition, diagnosis, and therapy of cerebral hernia development of crested chickens and other species.

S100 Proteins in Alzheimer's Disease

S100 proteins are calcium-binding proteins that regulate several processes associated with Alzheimer's disease (AD) but whose contribution and direct involvement in disease pathophysiology remains to be fully established. Due to neuroinflammation in AD patients, the levels of several S100 proteins are increased in the brain and some S100s play roles related to the processing of the amyloid precursor protein, regulation of amyloid beta peptide (Aβ) levels and Tau phosphorylation. S100 proteins are found associated with protein inclusions, either within plaques or as isolated S100-positive puncta, which suggests an active role in the formation of amyloid aggregates. Indeed, interactions between S100 proteins and aggregating Aβ indicate regulatory roles over the aggregation process, which may either delay or aggravate aggregation, depending on disease stage and relative S100 and Aβ levels. Additionally, S100s are also known to influence AD-related signaling pathways and levels of other cytokines. Recent evidence also suggests that metal-ligation by S100 proteins influences trace metal homeostasis in the brain, particularly of zinc, which is also a major deregulated process in AD. Altogether, this evidence strongly suggests a role of S100 proteins as key players in several AD-linked physiopathological processes, which we discuss in this review.

Inhibition of microRNA-124-3p as a novel therapeutic strategy for the treatment of Gulf War Illness: Evaluation in a rat model

Gulf War Illness (GWI) is a chronic, multisymptom illness that continues to affect up to 30% of veterans deployed to the Persian Gulf during the 1990-1991 Gulf War. After nearly 30 years, useful treatments for GWI are lacking and underlying cellular and molecular mechanisms involved in its pathobiology remain poorly understood, although exposures to pyridostigmine bromide (PB) and pesticides are consistently identified to be among the strongest risk factors. Alleviation of the broad range of symptoms manifested in GWI, which involve the central nervous system, the neuroendocrine system, and the immune system likely requires therapies that are able to activate and inactivate a large set of orchestrated genes. Previous work in our laboratory using an established rat model of GWI identified persistent elevation of microRNA-124-3p (miR-124) levels in the hippocampus whose numerous gene targets are involved in cognition-associated pathways and neuroendocrine function. This study aimed to investigate the broad effects of miR-124 inhibition in the brain 9 months after completion of a 28-day exposure regimen of PB, DEET (N,N-diethyl-3-methylbenzamide), permethrin, and mild stress by profiling the hippocampal expression of genes known to play a critical role in synaptic plasticity, glucocorticoid signaling, and neurogenesis. We determined that intracerebroventricular infusion of a miR-124 antisense oligonucleotide (miR-124 inhibitor; 0.05-0.5 nmol/day/28 days), but not a negative control oligonucleotide, into the lateral ventricle of the brain caused increased protein expression of multiple validated miR-124 targets and increased expression of downstream target genes important for cognition and neuroendocrine signaling in the hippocampus. Off-target cardiotoxic effects were revealed in GWI rats receiving 0.1 nmol/day as indicated by the detection in plasma of 5 highly elevated protein cardiac injury markers and 6 upregulated cardiac-enriched miRNAs in plasma exosomes determined by next-generation sequencing. Results from this study suggest that in vivo inhibition of miR-124 function in the hippocampus is a promising, novel therapeutic approach to improve cognition and neuroendocrine dysfunction in GWI. Additional preclinical studies in animal models to assess feasibility and safety by developing a practical, noninvasive drug delivery system to the brain and exploring potential adverse toxicologic effects of miR-124 inhibition are warranted.

The Effect of Traditional Chinese Medicine on Neural Stem Cell Proliferation and Differentiation

Neural stem cells (NSCs) are special types of cells with the potential for self-renewal and multi-directional differentiation. NSCs are regulated by multiple pathways and pathway related transcription factors during the process of proliferation and differentiation. Numerous studies have shown that the compound medicinal preparations, single herbs, and herb extracts in traditional Chinese medicine (TCM) have specific roles in regulating the proliferation and differentiation of NSCs. In this study, we investigate the markers of NSCs in various stages of differentiation, the related pathways regulating the proliferation and differentiation, and the corresponding transcription factors in the pathways. We also review the influence of TCM on NSC proliferation and differentiation, to facilitate the development of TCM in neural regeneration and neurodegenerative diseases.

S100A6 - focus on recent developments

The Ca2+-binding protein, S100A6, belongs to the S100 family. Binding of Ca2+ induces a conformational change, which causes an increase in the overall S100A6 hydrophobicity and allows it to interact with many targets. S100A6 is expressed in different normal tissues and in many tumors. Up to now it has been shown that S100A6 is involved in cell proliferation, cytoskeletal dynamics and tumorigenesis, and that it might have some extracellular functions. In this review, we summarize novel discoveries concerning S100A6 targets, its involvement in cellular signaling pathways, and presence in stem/progenitor cells, extracellular matrix and body fluids of diseased patients.

S100A6 protein: functional roles

S100A6 protein belongs to the A group of the S100 protein family of Ca2+-binding proteins. It is expressed in a limited number of cell types in adult normal tissues and in several tumor cell types. As an intracellular protein, S100A6 has been implicated in the regulation of several cellular functions, such as proliferation, apoptosis, the cytoskeleton dynamics, and the cellular response to different stress factors. S100A6 can be secreted/released by certain cell types which points to extracellular effects of the protein. RAGE (receptor for advanced glycation endproducts) and integrin β1 transduce some extracellular S100A6's effects. Dosage of serum S100A6 might aid in diagnosis in oncology.

Function of Metallothionein-3 in Neuronal Cells: Do Metal Ions Alter Expression Levels of MT3?

A study of factors proposed to affect metallothionein-3 (MT3) function was carried out to elucidate the opaque role MT3 plays in human metalloneurochemistry. Gene expression of Mt2 and Mt3 was examined in tissues extracted from the dentate gyrus of mouse brains and in human neuronal cell cultures. The whole-genome gene expression analysis identified significant variations in the mRNA levels of genes associated with zinc homeostasis, including Mt2 and Mt3. Mt3 was found to be the most differentially expressed gene in the identified groups, pointing to the existence of a factor, not yet identified, that differentially controls Mt3 expression. To examine the expression of the human metallothioneins in neurons, mRNA levels of MT3 and MT2 were compared in BE(2)C and SH-SY5Y cell cultures treated with lead, zinc, cobalt, and lithium. MT2 was highly upregulated by Zn²⁺ in both cell cultures, while MT3 was not affected, and no other metal had an effect on either MT2 or MT3.

Phenotypic and proteomic characteristics of human dental pulp derived mesenchymal stem cells from a natal, an exfoliated deciduous, and an impacted third molar tooth

The level of heterogeneity among the isolated stem cells makes them less valuable for clinical use. The purpose of this study was to understand the level of heterogeneity among human dental pulp derived mesenchymal stem cells by using basic cell biology and proteomic approaches. The cells were isolated from a natal (NDPSCs), an exfoliated deciduous (stem cells from human exfoliated deciduous (SHED)), and an impacted third molar (DPSCs) tooth of three different donors. All three stem cells displayed similar features related to morphology, proliferation rates, expression of various cell surface markers, and differentiation potentials into adipocytes, osteocytes, and chondrocytes. Furthermore, using 2DE approach coupled with MALDI-TOF/TOF, we have generated a common 2DE profile for all three stem cells. We found that 62.3 ± 7% of the protein spots were conserved among the three mesenchymal stem cell lines. Sixty-one of these conserved spots were identified by MALDI-TOF/TOF analysis. Classification of the identified proteins based on biological function revealed that structurally important proteins and proteins that are involved in protein folding machinery are predominantly expressed by all three stem cell lines. Some of these proteins may hold importance in understanding specific properties of human dental pulp derived mesenchymal stem cells.

S100A6 expression in keratinocytes and its impact on epidermal differentiation

S100A6 is a calcium binding protein expressed in many types of epithelia including epidermis. S100A6 is a binding partner of a number of proteins engaged in cytoskeletal organization, cell cycle control, stress response or apoptosis. So far the effect of its overexpression or knock-down on cell physiology has been studied only at the cellular level. Here, we used an in vitro model of differentiating epidermis to study the role of S100A6 at the tissue level and in the context of tissue differentiation. First of all we have shown that S100A6 mRNA level diminished several fold during primary keratinocyte differentiation and investigated the epigenetic and transcriptional mechanisms involved in this tight expression control. Using bisulfite treatment, luciferase assay and chromatin immunoprecipitation we found that changes in S100A6 expression were DNA methylation independent but could be orchestrated by epidermal specific factors: the ΔNp63 transcription factor and retinoic acid. To investigate if the drop-down in S100A6 expression is indeed critical for keratinocyte differentiation we developed HaCaT cells with stable S100A6 knock-down or overexpression and tested them in 2- and 3-dimensional (organotypic) culture conditions. S100A6 overexpressing cells exhibited accelerated proliferation, enhanced adhesion properties and suppressed loricrin expression - features typical for undifferentiated keratinocytes. In organotypic culture these cells formed thicker epidermis with more Ki67 positive cells, keratin 10 expression spatially limited to the uppermost cell layers and non-detectable loricrin expression. Together, results obtained in both culture models proved that increased S100A6 content in keratinocytes dramatically changed the pace and extent of epidermal differentiation.