Dual origin of mesenchymal stem cells contributing to organ growth and repair

In many adult tissues, mesenchymal stem cells (MSCs) are closely associated with perivascular niches and coexpress many markers in common with pericytes. The ability of pericytes to act as MSCs, however, remains controversial. By using genetic lineage tracing, we show that some pericytes differentiate into specialized tooth mesenchyme-derived cells--odontoblasts--during tooth growth and in response to damage in vivo. As the pericyte-derived mesenchymal cell contribution to odontoblast differentiation does not account for all cell differentiation, we identify an additional source of cells with MSC-like properties that are stimulated to migrate toward areas of tissue damage and differentiate into odontoblasts. Thus, although pericytes are capable of acting as a source of MSCs and differentiating into cells of mesenchymal origin, they do so alongside other MSCs of a nonpericyte origin. This study identifies a dual origin of MSCs in a single tissue and suggests that the pericyte contribution to MSC-derived mesenchymal cells in any given tissue is variable and possibly dependent on the extent of the vascularity.

Age-dependent fate and lineage restriction of single NG2 cells

NG2-expressing glia (NG2 cells, polydendrocytes) appear in the embryonic brain, expand perinatally, and persist widely throughout the gray and white matter of the mature central nervous system. We have previously reported that NG2 cells generate oligodendrocytes in both gray and white matter and a subset of protoplasmic astrocytes in the gray matter of the ventral forebrain and spinal cord. To investigate the temporal changes in NG2 cell fate, we generated NG2creER™BAC transgenic mice, in which tamoxifen-inducible Cre is expressed in NG2 cells. Cre induction at embryonic day 16.5, postnatal day (P) 2, P30 and P60 in mice that were double transgenic for NG2creER™BAC and the Cre reporter revealed that NG2 cells in the postnatal brain generate only NG2 cells or oligodendrocytes, whereas NG2 cells in the embryonic brain generate protoplasmic astrocytes in the gray matter of the ventral forebrain in addition to oligodendrocytes and NG2 cells. Analysis of cell clusters from single NG2 cells revealed that more than 80% of the NG2 cells in the P2 brain give rise to clusters consisting exclusively of oligodendrocytes, whereas the majority of the NG2 cells in the P60 brain generate clusters that contain only NG2 cells or a mixture of oligodendrocytes and NG2 cells. Furthermore, live cell imaging of single NG2 cells from early postnatal brain slices revealed that NG2 cells initially divide symmetrically to produce two daughter NG2 cells and that differentiation into oligodendrocytes occurred after 2-3 days.

Blockade of AT1 receptors protects the blood-brain barrier and improves cognition in Dahl salt-sensitive hypertensive rats

BACKGROUND

The present study tested the hypothesis that inappropriate activation of the brain renin-angiotensin system (RAS) contributes to the pathogenesis of blood-brain barrier (BBB) disruption and cognitive impairment during development of salt-dependent hypertension. Effects of an angiotensin II (AngII) type-1 receptor blocker (ARB), at a dose that did not reduce blood pressure, were also examined.

METHODS

Dahl salt-sensitive (DSS) rats at 6 weeks of age were assigned to three groups: low-salt diet (DSS/L; 0.3% NaCl), high-salt diet (DSS/H; 8% NaCl), and high-salt diet treated with ARB, olmesartan at 1 mg/kg.

RESULTS

DSS/H rats exhibited hypertension, leakage from brain microvessels in the hippocampus, and impaired cognitive functions, which were associated with increased brain AngII levels, as well as decreased mRNA levels of tight junctions (TJs) and collagen-IV in the hippocampus. In DSS/H rats, olmesartan treatment, at a dose that did not alter blood pressure, restored the cognitive decline, and ameliorated leakage from brain microvessels. Olmesartan also decreased brain AngII levels and restored mRNA expression of TJs and collagen-IV in DSS/H rats.

CONCLUSIONS

These results suggest that during development of salt-dependent hypertension, activation of the brain RAS contributes to BBB disruption and cognitive impairment. Treatment with an ARB could elicit neuroprotective effects in cognitive disorders by preventing BBB permeability, which is independent of blood pressure changes.

NG2 cells are not a major source of reactive astrocytes after neocortical stab wound injury

NG2 cells are an abundant glial cell type in the adult brain. They are distinct from astrocytes, mature oligodendrocytes, and microglia. NG2 cells generate oligodendrocytes and a subpopulation of protoplasmic astrocytes in the ventral forebrain during development. To determine whether NG2 cells generate reactive astrocytes in the lesioned brain, stab wound injury was created in adult NG2creBAC:ZEG double transgenic mice, in which enhanced green fluorescent protein (EGFP) is expressed in NG2 cells and their progeny, and the phenotype of the EGFP(+) cells was analyzed at 10 and 30 days post lesion (dpl). The majority (>90%) of the reactive astrocytes surrounding the lesion that expressed glial fibrillary acidic protein (GFAP) lacked EGFP expression, and conversely the majority (>90%) of EGFP(+) cells were GFAP-negative. However, 8% of EGFP(+) cells co-expressed GFAP at 10 dpl. Most of these EGFP(+) GFAP(+) cells were morphologically distinct from hypertrophic reactive astrocytes and exhibited weak GFAP expression. NG2 was detected in a fraction of the EGFP(+) GFAP(+) cells found at 10 dpl. By 30 dpl the number of EGFP(+) GFAP(+) cells had decreased more than four-fold from 10 dpl. A similar transient appearance of EGFP(+) GFAP(+) cells with simple morphology was observed in NG2creER™:ZEG double transgenic mice in which EGFP expression had been induced in NG2 cells prior to injury. NG2 cell-specific deletion of the oligodendrocyte lineage transcription factor Olig2 using NG2creER™:Olig2(fl/fl) :ZEG triple transgenic mice did not increase the number of EGFP(+) reactive astrocytes. These findings suggest that NG2 cells are not a major source of reactive astrocytes in the neocortex.

NG2 cells are uniformly distributed and NG2 is not required for barrel formation in the somatosensory cortex

The somatosensory barrel cortex in the rodent forms during the first postnatal week setting up a periphery related map with each whisker represented as a bundle of thalamocortical axons (TCAs) in layer IV. The centers of each barrel (hollows) contain the densely packed TCAs, while the areas between each barrel (septa) form a boundary between each barrel. NG2 chondroitin sulfate proteoglycan (CSPG) expressing cells (NG2 cells, polydendrocytes) make up a unique population of glial cells that receive synaptic like input and form close contacts with growing axons. In the present study we investigated the developmental distribution of NG2 cells in the barrel cortex to determine if they display preferential septa distribution similar to other extracellular and cell surface CSPGs. Immunohistochemistry for NG2 and platelet-derived growth factor receptor alpha (PDGFRα) in NG2DsRedBAC transgenic mice showed uniform distribution of NG2 cells and processes in barrel hollows and septa at postnatal (P) days 5, 6, 7, 8, 14, and 30. Changes in the barrel pattern formation caused by cauterization of one row of whiskers at P1 resulted in corresponding changes in extracellular and cell surface CSPG distribution at P7 but no detectable changes in NG2 cell bodies and processes. Furthermore, no abnormalities in barrel formation or reorganization were detected in NG2 knockout mice. These observations suggest that NG2 cells are unlikely to play an inhibitory boundary role on TCA growth and that NG2 expression is not necessary for normal barrel formation.

Non-stem cell origin for oligodendroglioma

Malignant astrocytic brain tumors are among the most lethal cancers. Quiescent and therapy-resistant neural stem cell (NSC)-like cells in astrocytomas are likely to contribute to poor outcome. Malignant oligodendroglial brain tumors, in contrast, are therapy sensitive. Using magnetic resonance imaging (MRI) and detailed developmental analyses, we demonstrated that murine oligodendroglioma cells show characteristics of oligodendrocyte progenitor cells (OPCs) and are therapy sensitive, and that OPC rather than NSC markers enriched for tumor formation. MRI of human oligodendroglioma also suggested a white matter (WM) origin, with markers for OPCs rather than NSCs similarly enriching for tumor formation. Our results suggest that oligodendroglioma cells show hallmarks of OPCs, and that a progenitor rather than a NSC origin underlies improved prognosis in patients with this tumor.

Astrocytes in the retrotrapezoid nucleus sense H+ by inhibition of a Kir4.1-Kir5.1-like current and may contribute to chemoreception by a purinergic mechanism

Central chemoreception is the mechanism by which CO(2)/pH sensors regulate breathing in response to tissue pH changes. There is compelling evidence that pH-sensitive neurons in the retrotrapezoid nucleus (RTN) are important chemoreceptors. Evidence also indicates that CO(2)/H(+)-evoked adenosine 5'-triphosphate (ATP) release in the RTN, from pH-sensitive astrocytes, contributes to chemoreception. However, mechanism(s) by which RTN astrocytes sense pH is unknown and their contribution to chemoreception remains controversial. Here, we use the brain slice preparation and a combination of patch-clamp electrophysiology and immunohistochemistry to confirm that RTN astrocytes are pH sensitive and to determine mechanisms by which they sense pH. We show that pH-sensitive RTN glia are immunoreactive for aldehyde dehydrogenase 1L1, a marker of astrocytes. In HEPES buffer the pH-sensitive current expressed by RTN astrocytes reversed near E(K(+)) (the equilibrium potential for K(+)) and was inhibited by Ba(2+) and desipramine (blocker of Kir4.1-containing channels), characteristics most consistent with heteromeric Kir4.1-Kir5.1 channels. In bicarbonate buffer, the sodium/bicarbonate cotransporter also contributed to the CO(2)/H(+)-sensitive current in RTN astrocytes. To test the hypothesis that RTN astrocytes contribute to chemoreception by a purinergic mechanism, we used fluorocitrate to selectively depolarize astrocytes while measuring neuronal activity. We found that fluorocitrate increased baseline activity and pH sensitivity of RTN neurons by a P2-receptor-dependent mechanism, suggesting that astrocytes may release ATP to activate RTN chemoreceptors. We also found in bicarbonate but not HEPES buffer that P2-receptor antagonists decreased CO(2) sensitivity of RTN neurons. We conclude that RTN astrocytes sense CO(2)/H(+) in part by inhibition of a Kir4.1-Kir5.1-like current and may provide an excitatory purinergic drive to pH-sensitive neurons.

Aliskiren inhibits intracellular angiotensin II levels without affecting (pro)renin receptor signals in human podocytes

BACKGROUND

A direct renin inhibitor (DRI) had a benefit in decreasing albuminuria in type 2 diabetic patients having already been treated with angiotensin (Ang) II type 1 receptor blocker (ARB), suggesting that aliskiren may have another effect other than blockade of the traditional renin-angiotensin system (RAS). Recently, prorenin bound to (pro)renin receptor ((P)RR) was found and shown to evoke two pathways; the generation of Ang peptides and the receptor-dependent activation of extracellular signal-related protein kinase (ERK). Because (P)RR is present in the podocytes, a central component of the glomerular filtration barrier, we hypothesized that aliskiren influences the (P)RR-induced two pathways in human podocytes.

METHODS

Human podocytes were treated with 2 nmol/l prorenin in the presence and absence of an angiotensin-converting enzyme inhibitor (ACEi) imidaprilat, an ARB candesartan, a DRI aliskiren, or the siRNA knocking down the (P)RR mRNA and the intracellular AngII levels and the phosphorylation of ERK were determined.

RESULTS

The expression of (P)RR mRNA of human podocytes was unaffected by the treatment with RAS inhibitors, but decreased by 69% with the siRNA treatment. The basal levels of intracellular AngII and the prorenin-induced increase in intracellular AngII were significantly reduced by aliskiren and siRNA treatment, compared with imidaprilat and candesartan. The prorenin-induced ERK activation was reduced to control level by the siRNA treatment, but it was unaffected by imidaprilat, candesartan, or aliskiren.

CONCLUSIONS

Aliskiren is the most potent inhibitor of intracellular AngII levels of human podocytes among RAS inhibitors, although it is incapable of inhibiting the (P)RR-dependent ERK phosphorylation.

NG2 cells: Properties, progeny and origin

The NG2 proteoglycan is a type 1-transmembrane protein expressed by a range of cell types within and outside the mammalian nervous system. NG2-expressing (NG2) cells are found in grey and white matter tracts of the developing and adult CNS and have previously been assumed to represent oligodendrocyte precursor cells: new work using transgenic mice has shown that NG2 cells generate oligodendrocytes, protoplasmic astrocytes and in some instances neurons in vivo. NG2 cells express GABAA receptors and the AMPA subtype of glutamate receptors. They make intimate contact to neurons prior to myelinating axons and also form electron-dense synaptic specialisations with axons in the cerebellum, cortex and hippocampus and with non-myelinated axons in the corpus callosum. These synaptic NG2 cells respond to neuronal release of glutamate and GABA. This neuron-glia interaction may thus regulate the differentiation and proliferation of NG2 cells. The C-terminal PDZ-binding motif of the NG2 protein binds several PDZ proteins including Mupp1, Syntenin and the Glutamate Receptor Interacting Protein (GRIP). Since GRIP can bind subunits of the AMPA receptors expressed by NG2 cells, the interaction between GRIP and NG2 may orientate the glial AMPA receptors towards sites of neuronal glutamate release. The origin, heterogeneity and function of NG2 cells as modulators of the neuronal network are important incompletely resolved questions.

Hydrophobic residues in helix 8 of cannabinoid receptor 1 are critical for structural and functional properties

In addition to the heptahelical transmembrane domain shared by all G protein-coupled receptors (GPCRs), many class A GPCRs adopt a helical domain, termed helix 8, in the membrane-proximal region of the C terminus. We investigated the role of residues in the hydrophobic and hydrophilic faces of amphiphilic helix 8 of human cannabinoid receptor 1 (CB1). To differentiate between a role for specific residues and global features, we made two key mutants: one involving replacement of the highly hydrophobic groups, Leu404, Phe408, and Phe412, all with alanine and the second involving substitution of the basic residues, Lys402, Arg405, and Arg409, all with the neutral glutamine. The former showed a very low B(max) based on binding isotherms, a minimal E(max) based on GTPgammaS binding analysis, and defective localization relative to the wild-type CB1 receptor as revealed by confocal microscopy. However, the latter mutant and the wild-type receptors were indistinguishable. Circular dichroism spectroscopy of purified peptides with corresponding sequences indicated that the highly hydrophobic residues are critical for maintaining a strong helical structure in detergent, whereas the positively charged residues are not. Further investigation of mutant receptors revealed that CB1 localization requires a threshold level of hydrophobicity but not specific amino acids. Moreover, mutant receptors carrying two- to six-residue insertions amino-terminal to helix 8 revealed a graded decrease in B(max) values. Our results identify the key helix 8 components (including hydrophobicity of specific residues, structure, and location relative to TM7) determinant for receptor localization leading to robust ligand binding and G protein activation.

Beta1 integrins are required for normal CNS myelination and promote AKT-dependent myelin outgrowth

Oligodendrocytes in the central nervous system (CNS) produce myelin sheaths that insulate axons to ensure fast propagation of action potentials. beta1 integrins regulate the myelination of peripheral nerves, but their function during the myelination of axonal tracts in the CNS is unclear. Here we show that genetically modified mice lacking beta1 integrins in the CNS present a deficit in myelination but no defects in the development of the oligodendroglial lineage. Instead, in vitro data show that beta1 integrins regulate the outgrowth of myelin sheaths. Oligodendrocytes derived from mutant mice are unable to efficiently extend myelin sheets and fail to activate AKT (also known as AKT1), a kinase that is crucial for axonal ensheathment. The inhibition of PTEN, a negative regulator of AKT, or the expression of a constitutively active form of AKT restores myelin outgrowth in cultured beta1-deficient oligodendrocytes. Our data suggest that beta1 integrins play an instructive role in CNS myelination by promoting myelin wrapping in a process that depends on AKT.

[Polydendrocytes--their roles in development and glial tumor formation]

Polydendrocytes or NG2 cells are the fourth major glial cell type observed in the mammalian central nervous system (CNS) that is distinct from neurons, mature oligodendrocytes, astrocytes, or microglia. They can be identified on the basis of the expression of NG2 proteoglycan and are distributed throughout the gray matter and white matter both in the developing and mature CNS. Although polydendrocytes were earlier regarded as oligodendrocyte progenitor cells, recent studies using Cre/loxP fate mapping provided the first direct evidence that endogenous polydendrocytes give rise to oligodendrocytes in vivo. In addition, the same technique showed that polydendrocytes differentiate into a subpopulation of astrocytes in a region-specific manner. On the other hand, it is highly debatable whether polydendrocytes generate neurons. Although some studies suggest the possibility that polydendrocytes produce neurons, other studies do not support this hypothesis. The possibility that polydendrocytes contribute to the formation of gliomas has been suggested in a number of clinical and basic experimental studies. In this review, we present both classical findings (and the latest reports on the basic characteristics of this cell type).

NG2 cells are distinct from neurogenic cells in the postnatal mouse subventricular zone

NG2 cells express the chondroitin sulfate proteoglycan NG2 and are a fourth type of glia distinct from astrocytes, oligodendrocytes, and microglia. NG2 cells generate oligodendrocytes but have also been reported to represent neuronal progenitor cells in the postnatal mouse subventricular zone (SVZ). We performed a detailed immunohistochemical analysis of NG2 cells in the mouse SVZ, rostral migratory stream (RMS), and olfactory bulb granule cell layer (OB GCL), which constitute a neurogenic niche in the postnatal forebrain. NG2 cells in the SVZ and RMS expressed the oligodendrocyte precursor cell antigen platelet-derived growth factor receptor-alpha but did not express antigens known to be expressed by neuronogenic cells in the SVZ, such as doublecortin, PSA-NCAM, beta-tubulin, Dlx2, or GFAP. More than 99.5% of the proliferating cells in the SVZ were NG2 negative. In the olfactory bulb, NG2 cells were found to generate primarily oligodendrocytes and a small number of astrocytes but not neurons. In the SVZ and RMS, NG2 cells were sparse and made up a much smaller fraction of the cells compared with the surrounding nonneurogenic parenchyma. Parenchymal NG2 cells were often located along the border of the SVZ and RMS. The abundance of NG2 cells increased in the distal parts of the RMS and especially in the OB GCL, where NG2 cell processes were seen in close proximity to many maturing interneurons. Our findings indicate that NG2 cells do not represent neuronal progenitor cells in the postnatal SVZ but are likely to be oligodendrocyte precursor cells.

Effects of neoadjuvant chemotherapy on primary tumor and lymph node metastasis in esophageal squamous cell carcinoma: additive association with prognosis

Neoadjuvant chemotherapy (NACT) is widely used to treat esophageal squamous cell carcinoma with lymph node metastasis (ESCC). However, NACT frequently has differential effects on primary tumor (PT) and lymph node metastasis (LNM). The clinical significance of this phenomenon remains unclear. Reduction in tumor size of PT and LNM was evaluated separately in 47 node-positive ESCC patients undergoing NACT, followed by surgical resection. We analyzed the prognostic significance and various clinicopathological parameters. NACT resulted in an average reduction rate of 45.5% for PT and 36.6% for LNM; the correlation between these rates was weak but significant (r(2) = 0.122, P = 0.016). The reduction rates in both PT and LNM were significant prognostic factors, with the maximal significance with cut-off at 30% size reduction for PT (3-year survival, 47.3 vs. 8.3%, P = 0.0004) and 20% for LNM (51.3 vs. 7.1%, P = 0.0013). When these cut-off values were used to define NACT response, 28 patients (59%) were deemed responders for both PT and LNM, while 7 (15%) were nonresponders for both, and the response was inconsistent in 12 patients (26%). Only both PT/LNM responders showed good survival rates, with the remaining categories showing poor survival (3-year survival 60.5 vs. 5.3% P < 0.0001). Multivariate analysis identified neither the PT nor the LNM response alone as an independent prognostic factor; however the combined PT/LNM response was identified as an independent prognostic factor (hazard ratio [HR] 2.861, P = 0.0255) in addition to the number of histological lymph node metastases (HR 2.551, P = 0.0328). The response to NACT in LNM and PT correlates closely with postoperative survival. A good response in both enhances the postoperative prognosis.

Dystrophin nonsense mutations can generate alternative rescue transcripts in lymphocytes

Secondary alterations in splicing have been reported to produce semi-functional mRNA from several nonsense mutations in the dystrophin gene. Disruptions of exonic splicing enhancers by single nucleotide changes are thought to underlie such alterations. The precise frequencies of such nonsense mutation-dependent splicing alterations, however, remain unknown. Here we analyzed the splicing patterns of dystrophin mRNA in lymphocytes from 38 patients with dystrophinopathies due to nonsense mutations in the dystrophin gene. In seven of the cases (18%), we observed partial skipping of the nonsense-encoding exon. Two of the seven cases, however, exhibited complex activation of a nonsense mutation-created splice site, which resulted in the generation of novel transcripts. Examination of cis-regulatory splicing elements through calculation of splicing probability scores and identification of potential splicing enhancer or silencer sequences failed to disclose a single cause for exon skipping. Remarkably, individual differences in splicing patterns were observed for cells from patients with identical nonsense mutations (C.5899C>T). Although five cases produced semi-functional dystrophin mRNAs, only one of these exhibited a mild clinical course. These results provide important insights about targets for exon skipping induced by candidate antisense oligonucleotides and for ribosomal read-through of nonsense mutations.

Effect of direct retainer and major connector designs on RPD and abutment tooth movement dynamics

Designs of removable partial dentures are suggested to affect the mobility of abutment teeth and removable partial denture (RPD) during oral functions. This study aimed to examine the effect of direct retainer and major connector designs on RPD dynamics under simulated loading. Six different Kennedy class II maxillary RPDs were fabricated on a maxillary model. These dentures involved 3 different direct retainers (wrought-wire clasp, RPA clasp, and conical crown telescopic retainer) and 2 different major connectors (Co-Cr major connector and heat-cured acrylic resin with a metal strengthener). Using an experimental model with simulated periodontal ligaments and mucosa that were fabricated using silicone impression material, three-dimensional displacements of the RPDs were measured under a simulated 30-N loading with a displacement transducer type M-3. Significant effects of "direct retainer design" on bucco-palatal displacements and "major connector" on mesio-distal displacements were revealed by 2 x 3 two-way analysis of variance of abutment teeth movements (P < 0.001 and P = 0.002, respectively). Additionally, analysis of variance of RPD displacements revealed significant effects of "direct retainer design" on corono-apical displacements and "major connector" on mesio-distal displacements (P = 0.001 and P = 0.028, respectively). Rigid direct retainers and rigid major connectors decrease the movements of both abutment tooth and RPD.