Correlation between the Human Development Index and the Incidence and Mortality of Non-Hodgkin Lymphoma

OBJECTIVE

This study was to examine the relationship between socioeconomic status and the incidence and mortality of non-Hodgkin lymphoma (NHL).

METHODS

We compared the age-standardized incidence rate (ASIR), age-standardized mortality rate (ASMR), and the ASMR to ASIR ratio (MIR) at national and regional levels and studied the correlation between the MIR and the human development index (HDI) in 2012 and 2018.

RESULTS

The highest ASIR was in North America in 2012 and in Australia in 2018, and the lowest ASIR was in Central and South Asia in both 2012 and 2018. The highest ASMR was in North Africa in both 2012 and 2018, and the lowest ASMR was in Eastern Asia and South-Central Asia in 2012 and in South-Central Asia in 2018. The lowest MIR was in Australia in both 2012 and 2018, and the highest MIR was in Western Africa in both 2012 and 2018. HDI was strongly negatively correlated with MIR (r: -0.8810, P<0.0001, 2012; r: -0.8895, P<0.0001, 2018). Compared to the 2012 data, the MIR in the intermediate HDI countries significantly deceased and the HDI in low and high HDI countries significantly increased in 2018.

CONCLUSION

The MIR is negatively correlated with HDI. Increasing the HDI in low and intermediate HDI countries may reduce the MIR and increase the survival of patients with NHL.

Ligand symmetry significantly affects spin crossover behaviour in isomeric [Fe(pybox)2]2+ complexes

The understanding of the correlation between the spin-state behaviour and the structural features in transition-metal complexes is of pronounced importance to the design of spin crossover compounds with high performance. However, the study of the influence of ligand symmetry on the spin crossover properties is still limited due to the shortage of suitable structural systems. Herein we report the magneto-structural correlations of three mononuclear Fe(ii) isomers with respect to their ligand symmetry. In this work, two phenyl-substituted meso and optically pure pybox ligands were employed to construct meso (1), optically pure (2), and racemic (3) ligand types of [Fe(pybox)₂]²⁺ complexes. Their magnetic susceptibilities were measured via temperature-dependent paramagnetic ¹H NMR spectroscopy. We fitted the midpoint temperatures of the transition (T_1/2) of 260 K for 1(ClO₄), 247 K for 2(ClO₄), and 281 K for 3(ClO₄). The influence of structural symmetry on spin crossover was rationalized through density functional theory calculations. The optimized structures of [Fe(pybox)₂]²⁺ complex cations show that the geometric distortion of the central FeN₆ coordination sphere is mainly caused by the steric congestions between adjacent phenyl substituents. In these compounds, there is a distinct correlation that more steric congestions produce larger coordination distortion and favor the electron configuration in the high-spin state, which reflects in the increase of T_1/2. Additionally, the influence of the counter anion and lattice solvent on the meso series compounds was inspected. It is revealed that multiple factors dominate the spin-state behaviour in the solid state. This work provides deep insight into the effect of ligand symmetry on the spin transition behaviour in spin crossover compounds. It demonstrates that molecular symmetry should be considered in the design of spin crossover compounds.

Construction of SCO-Active Fe(II) Mononuclear Complexes from the Thio-pybox Ligand

The development of new spin-crossover complexes provides novel promising switching materials with significant potential at the molecular level. Ter-imine-type molecules represent one of the important classes of ligands in creating SCO-active complexes. Herein we report a family of mononuclear Fe(II) SCO-active compounds constructed from a new type of ter-imine ligand named the thio-pybox ligand (2,6-bis(4,4-dimethyl-4,5-dihydrothiazol-2-yl)pyridine, L¹). Through the variation of counteranions, some cases display complete SCO and with T_1/2 near ambient temperature. Among them, annealed [Fe^II(L¹)₂](ClO₄)₂ [1(ClO₄)] shows T_1/2↓ and T_1/2↑ as 319 and 349 K, respectively. The wide thermal hysteresis of ΔT = 30 K originated from the weak interaction between complex cations and counteranions in the crystal lattice. Impressively, its high-spin population can be increased considerably by annealing at high temperature. The metastable high-spin phase is stable in the successive magnetic measurements and would gradually relax to its initial state with high population of low-spin configuration at ambient temperature. In acetonitrile-diluted solution, 1(ClO₄) still maintains SCO with an estimated T_1/2 at 240 K. Differential scanning calorimetry discloses the structural phase at around 355 K in the first heating process and the increase in the high-spin population concomitant with annealing was also corroborated by ⁵⁷Fe Mössbauer measurements. Additionally, the influences on SCO by counteranion and ligand structure are investigated, which show that the fine tuning of complex structures can affect the behavior of the spin state significantly. Finally, magneto-structural correlation studies were performed on the structures of 1(ClO₄) and its oxygen analogue at multiple temperatures. The analyses of some structural parameters, including terminal N···N donor separation, bite angle, patulous angle, and the root mean squared deviation indicate that the replacement of the oxygen atom with a sulfur atom can effectively improve the flexibility and release the steric strain and thus tune the SCO toward ambient temperature. Our research demonstrates the rational design of the ligand can lead to new SCO-active compounds with high performance.

Spin crossover and structural phase transition in homochiral and heterochiral Fe[(pybox)2]2+ complexes

Spin crossover and structural phase transition were discovered in three pairs of homochiral and heterochiral [Fe(pybox)₂]²⁺ diastereomers.

[Effect of the ischemic post-conditioning on the prevention of the cardio-renal damage in patients with acute ST-segment elevation myocardial infarction after primary percutaneous coronary intervention]

Objective: To evaluate the effect of the ischemic post-conditioning (IPC) on the prevention of the cardio-renal damage in patients with acute ST-segment elevation myocardial infarction (STEMI) after primary percutaneous coronary intervention (PPCI). Methods: A total of 251 consecutive STEMI patients underwent PPCI in the heart center of Tianjin Third Central Hospital from January 2012 to June 2014 were enrolled in this prospective, randomized, control, single-blinded, clinical registry study. Patients were randomly divided into IPC group (123 cases) and control group (128 cases) with random number table. Patients in IPC group underwent three times of inflation/deflation with low inflation pressure using a balloon catheter within one minute after culprit vessel blood recovery, and then treated by PPCI. Patients in control group received PPCI procedure directly. The basic clinical characteristics, incidence of reperfusion arrhythmia during the procedure, the rate of electrocardiogram ST-segment decline, peak value of myocardial necrosis markers, incidence of contrast induced acute kidney injury(CI-AKI), and one-year major adverse cardiovascular events(MACE) which including myocardial infarction again, malignant arrhythmia, rehospitalization for heart failure, repeat revascularization, stroke, and death after the procedure were analyzed between the two groups. Results: The age of IPC group and control group were comparable((61.2±12.6) vs. (64.2±12.1) years old, P=0.768). The incidence of reperfusion arrhythmia during the procedure was significantly lower in the IPC group than in the control group(42.28% (52/123) vs. 57.03% (73/128), P=0.023). The rate of electrocardiogram ST-segment decline immediately after the procedure was significantly higher in the IPC group than in the control group (77.24% (95/123) vs. 64.84% (83/128), P=0.037). The peak value of myocardial necrosis markers after the procedure were significantly lower in the IPC group than in the control group(creatine kinase: 1 257 (682, 2 202) U/L vs. 1 737(794, 2 816)U/L, P=0.029; creatine kinase-MB: 123(75, 218)U/L vs.165(95, 288)U/L, P=0.010). The rate of CI-AKI after the procedure was significantly lower in the IPC group than in the control group(5.69%(7/123) vs. 14.06%(18/128), P=0.034). The rate of the one-year MACE was significantly lower in the IPC group than in the control group(7.32%(9/123) vs. 15.63% (20/128), P=0.040). Conclusion: The IPC strategy performed eight before PPCI can reduce myocardial ischemia- reperfusion injury, decline the rates of CI-AKI and one-year MACE significantly in STEMI patients, thus has a significant protective effect on heart and kidney in STEMI patients. Clinical Trial Registration Chinese Clinical Trials Registry, ChiCTR-ICR-15006590.

Analysis of antithrombotic therapy in elderly patients with atrial fibrillation

This study aimed to analyze the impact factors and outcome of antithrombotic therapy in elderly patients over 65 years old that suffered from atrial fibrillation (AF). A total of 256 elderly patients with AF over 65 years old were divided into 3 groups: 65-74 years old (N = 86), 75-84 years old (N = 122), and over 85 years old (N = 48). The clinical characteristics, antithrombotic therapy, and its related impact factors were retrospectively analyzed. Of all patients, 187 received antithrombotic therapy. In the 65-74 year-old group, 78 patients received antiplatelet treatment (90.7%) and 5 patients received anticoagulation treatment (5.8%). In the 75-84 year-old group, 76 patients received antiplatelet treatment (62.3%) and 14 patients received anticoagulation treatment (11.5%). In the group of over 85 year-olds, 33 patients received antiplatelet therapy (68.8%) and 4 patients received anticoagulation treatment (8.3%). Eleven patients had deep vein thrombosis and atrial thrombosis during antiplatelet therapy (5.9%), 5 patients had gastrointestinal hemorrhage after antiplatelet therapy (2.7%), 2 patients had gastrointestinal bleeding, and 3 patients had brain hemorrhage after anticoagulation treatment (21.7%). Suboptimal antithrombotic therapy was observed in the elderly patients with AF, partly owing to the risks of both thromboembolism and bleeding.

Dynamics of notch expression during murine prostate development and tumorigenesis

Notch signaling has been widely demonstrated to be responsible for cell fate determination during normal development and implicated in human T-cell leukemia and mouse mammary carcinomas. Here we show that Notch signaling may be involved in prostatic development and cancer cell growth. In situ hybridization and reverse transcription-PCR analyses revealed that Notch1 was expressed in prostate epithelial cells during normal development and in prostate cancer cells. Characterization of Notch1-green fluorescent protein transgenic mice, in which the expression of reporter green fluorescent protein is under the control of the Notch1 promoter, indicated that Notch1-expressing cells were associated with the basal epithelial cell population in the prostate. Examination of the transgenic adenocarcinoma of the mouse prostate showed that expression of Notch1 was elevated in malignant prostatic epithelial cells of primary and metastatic tumors. Expression of Notch ligands, however, was low or undetectable in cultured prostate cancer cells or in malignant prostatic epithelial cells in transgenic adenocarcinoma of the mouse prostate. Furthermore, overexpression of a constitutively active form of Notch1 inhibited the proliferation of various prostate cancer cells, including DU145, LNCaP, and PC3 cells. Taken together, our data indicate for the first time that Notch signaling may play a role in murine prostatic development and tumorigenesis.

[The study of transfected cardiomyocytes by recombinant adenovirus and adeno-associated virus]

AIM AND METHODS

Recombinant adenovirus (rAd) and adeno-associated virus (rAAV) were created, in which beta2-adrenergic receptors (beta2-AR) gene is under control of the cmv promotor, the cultured neonate rat ventricular myocytes were infected by the two vectors, and the expression of beta2-AR on cultured neonate rat ventricular myocytes was assessed.

RESULTS

RT-PCR demonstrated the presence of beta2-AR mRNA, protein immunoblots demonstrated the expression of the beta2-AR gene. According to a ligand binding assay, the density of beta AR in the cardiomyocytes infected by rAd and rAAV had no difference, which was greater than that in the control.

CONCLUSION

The results above demonstrated that adenovirus vector and AAV vector transfected efficiently cardiomyocytes.

Hes1 is a negative regulator of inner ear hair cell differentiation

Hair cell fate determination in the inner ear has been shown to be controlled by specific genes. Recent loss-of-function and gain-of-function experiments have demonstrated that Math1, a mouse homolog of the Drosophila gene atonal, is essential for the production of hair cells. To identify genes that may interact with Math1 and inhibit hair cell differentiation, we have focused on Hes1, a mammalian hairy and enhancer of split homolog, which is a negative regulator of neurogenesis. We report here that targeted deletion of Hes1 leads to formation of supernumerary hair cells in the cochlea and utricle of the inner ear. RT-PCR analysis shows that Hes1 is expressed in inner ear during hair cell differentiation and its expression is maintained in adulthood. In situ hybridization with late embryonic inner ear tissue reveals that Hes1 is expressed in supporting cells, but not hair cells, of the vestibular sensory epithelium. In the cochlea, Hes1 is selectively expressed in the greater epithelial ridge and lesser epithelial ridge regions which are adjacent to inner and outer hair cells. Co-transfection experiments in postnatal rat explant cultures show that overexpression of Hes1 prevents hair cell differentiation induced by Math1. Therefore Hes1 can negatively regulate hair cell differentiation by antagonizing Math1. These results suggest that a balance between Math1 and negative regulators such as Hes1 is crucial for the production of an appropriate number of inner ear hair cells.

Two-amino acid molecular switch in an epithelial morphogen that regulates binding to two distinct receptors

Ectodysplasin, a member of the tumor necrosis factor family, is encoded by the anhidrotic ectodermal dysplasia (EDA) gene. Mutations in EDA give rise to a clinical syndrome characterized by loss of hair, sweat glands, and teeth. EDA-A1 and EDA-A2 are two isoforms of ectodysplasin that differ only by an insertion of two amino acids. This insertion functions to determine receptor binding specificity, such that EDA-A1 binds only the receptor EDAR, whereas EDA-A2 binds only the related, but distinct, X-linked ectodysplasin-A2 receptor (XEDAR). In situ binding and organ culture studies indicate that EDA-A1 and EDA-A2 are differentially expressed and play a role in epidermal morphogenesis.

Overexpression of Math1 induces robust production of extra hair cells in postnatal rat inner ears

For mammalian cochlear hair cells, fate determination is normally completed by birth. We report here that overexpression of Math1, a mouse homolog of the Drosophila gene atonal, in postnatal rat cochlear explant cultures resulted in extra hair cells. Surprisingly, we found that the source of the ectopic hair cells was columnar epithelial cells located outside the sensory epithelium in the greater epithelial ridge, which normally give rise to inner sulcus cells. Moreover, Math1 expression also facilitated conversion of postnatal utricular supporting cells into hair cells. Thus Math1 was sufficient for the production of hair cells in the ear, and immature postnatal mammalian inner ears retained the competence to generate new hair cells.

Role of neurotrophins and lectins in prevention of ototoxicity

Degeneration of hair cells (HC) and/or spiral ganglion neurons (SGN) is a major cause of hearing loss. Postnatal rat cochlear explant cultures are used to study the toxic actions of different classes of ototoxins and to identify molecules that can protect SGN and HC from ototoxic damage. Various ototoxins induce differential damage to HC and/or SGN. While gentamicin preferentially causes HC death, sodium salicylate selectively induces degeneration of SGN. In contrast, cisplatin results in destruction of both SGN and HC. Specific neurotrophins, including NT-4/5, BDNF, and NT-3, greatly protect SGN from all three types of ototoxins. In contrast, NGF and other growth factors have no effect. Of the 51 compounds examined, only concanavalin A (Con A), a lectin molecule, significantly protects HC from gentamicin. A dose-dependent study of Con A shows that maximal protection occurred at 100 nM. Further experiments indicates that preincubation of Con A with gentamicin does not form a complex, and coaddition of Con A and gentamicin to bacterial cultures, such as E. Coli cultures, does not interfere with the antibiotic activity of gentamicin. When the other 21 lectins are examined, Erythrina cristagalli lectin and Detura stramonium lectin also show activity similar to Con A. These findings may help elucidate the mechanisms of ototoxins and suggest that specific neurotrophins and lectins may be of therapeutic value in the prevention of ototoxin-induced hearing loss.

Heregulin enhances regenerative proliferation in postnatal rat utricular sensory epithelium after ototoxic damage

Hair cell loss due to acoustic and ototoxic damage often leads to hearing and balance impairments. Although a spontaneous event in chicks and lower vertebrates, hair cell replacement occurs at a much lower frequency in mammals presumably due to a very low rate of supporting cell proliferation following injury. We report here that heregulin, a member of the neuregulin family, dramatically enhances proliferation of supporting cells in postnatal rat utricular epithelial sheet cultures after gentamicin treatment, as revealed by bromo-deoxyuridine (BrdU) immunocytochemistry. A dose-dependent study shows that the maximal effects of heregulin are achieved at 3 nM. The mitogenic effects of heregulin are confirmed in utricular whole mount cultures. Autoradiography of the utricular whole mount cultures shows that heregulin also enhances the number of tritiated thymidine-labeled cells within the hair cell layer. TaqMan quantitative RT-PCR analysis and immunocytochemistry reveal that heregulin and its binding receptors (ErbB-2, ErbB-3 and ErbB-4) are expressed in the inner ear sensory epithelium. Of several ligands activating various ErbB receptors, including heregulin, neuregulin-3, beta-cellulin, heparin binding-epidermal growth factor (HB-EGF), transforming growth factor-alpha (TGF-alpha) and EGF, heregulin shows the most potent mitogenic effects on supporting cells. Because neuregulin-3 that signals only through ErbB-4 does not show an effect, these data suggest that activation of the ErbB-2-ErbB-3 heterodimeric complexes, rather than ErbB-4, is critical for the proliferative response in the utricular sensory epithelium. In addition, gentamicin treatment induces an upregulation of heregulin mRNA. Considered together, heregulin may play an important role in hair cell regeneration following ototoxic damage.

Transgene expression in the guinea pig cochlea mediated by a lentivirus-derived gene transfer vector

The utility of lentivirus as a gene delivery vector in the cochlea was evaluated in vitro and in vivo. Lentivirus transduction was assessed through expression analysis of a reporter gene, green fluorescent protein (GFP), integrated within the viral genome. In vitro characterization of lentivirus-GFP was assessed by infection of explants from cochleas of neonatal rat. The lentiviral vector transduced both spiral ganglion neurons (SGNs) and glial cells. In vivo characterization of lentivirus-GFP was assessed by directly infusing the vector into the guinea pig cochlea via an osmotic minipump. Sections of lentivirus-infused cochlea revealed a highly restricted fluorescence pattern limited to the periphery of the perilymphatic space. Transduction of SGNs and glial cells by lentivirus in vitro but not in vivo suggests limited dissemination of the viral vector from the perilymphatic space. The cellular and tissue architecture of the lentivirus-infused cochlea was intact and free of inflammation. Restricted transduction of cell types confined to the periphery of the perilymphatic space by the lentivirus is ideal for stable production of gene products secreted into the perilymph.

Concanavalin A protects hair cells against gentamicin ototoxicity in rat cochlear explant cultures

Degeneration of hair cells and spiral ganglion neurons due to acoustic trauma and various ototoxins is a major cause of hearing loss. Although our previous study demonstrates that specific neurotrophins protect spiral ganglion neurons from ototoxic insult, they do not protect hair cells. In the present experiments, we used postnatal rat cochlear explant cultures to identify molecules that protect hair cells from ototoxic damage. Of 51 compounds examined, only concanavalin A (Con A) significantly protected hair cells from gentamicin. A dose-dependent study of Con A showed that maximal protection occurred at 100 nM. The protective effects of Con A on hair cells were confirmed with confocal microscopy and paraffin sectioning of the cultures. Several experiments were performed to examine the mechanism of protection by Con A. Incubation of Con A with gentamicin did not form a complex and coaddition of Con A and gentamicin to Escherichia coli cultures did not interfere with the antibiotic activity of gentamicin. However, Lyso-Tracker staining and gentamicin immunocytochemistry provided evidence that preincubation with Con A blocked gentamicin uptake into hair cells. Considered together, these findings may help elucidate the ototoxic mechanism of aminoglycoside antibiotics, and suggest that Con A may be of therapeutic value in prevention of aminoglycoside-induced hearing loss.

IGF-I deficient mice show reduced peripheral nerve conduction velocities and decreased axonal diameters and respond to exogenous IGF-I treatment

Although insulin-like growth factor-I (IGF-I) can act as a neurotrophic factor for peripheral neurons in vitro and in vivo following injury, the role IGF-I plays during normal development and functioning of the peripheral nervous system is unclear. Here, we report that transgenic mice with reduced levels (two genotypes: heterozygous Igf1+/- or homozygous insertional mutant Igf1m/m) or totally lacking IGF-I (homozygous Igf1-/-) show a decrease in motor and sensory nerve conduction velocities in vivo. In addition, A-fiber responses in isolated peroneal nerves from Igf1+/- and Igf1-/- mice are impaired. The nerve function impairment is most profound in Igf1-/- mice. Histopathology of the peroneal nerves in Igf1-/- mice demonstrates a shift to smaller axonal diameters but maintains the same total number of myelinated fibers as Igf1+/+ mice. Comparisons of myelin thickness with axonal diameter indicate that there is no significant reduction in peripheral nerve myelination in IGF-I-deficient mice. In addition, in Igf1m/m mice with very low serum levels of IGF-I, replacement therapy with exogenous recombinant hIGF-I restores both motor and sensory nerve conduction velocities. These findings demonstrate not only that IGF-I serves an important role in the growth and development of the peripheral nervous system, but also that systemic IGF-I treatment can enhance nerve function in IGF-I-deficient adult mice.

Immunocytochemical and morphological evidence for intracellular self-repair as an important contributor to mammalian hair cell recovery

Although recent studies have provided evidence for hair cell regeneration in mammalian inner ears, the mechanism underlying this regenerative process is still under debate. Here we report immunocytochemical, histological, electron microscopic, and autoradiographic evidence that, in cultured postnatal rat utricles, a substantial number of hair cells can survive gentamicin insult even their stereocilia are lost. These partially damaged hair cells can survive for a prolonged time and regrow the stereocilia. Although the number of stereocilia-bearing hair cells increases over time after gentamicin insult, hair cell and supporting cell numbers remain essentially unchanged. Tritiated thymidine autoradiography and bromodeoxyuridine immunocytochemistry of the cultures demonstrate that cell proliferation in the sensory epithelium is very limited and is far below the number of recovered hair cells. Furthermore, terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling analysis indicates that gentamicin-induced apoptosis in the sensory epithelium occurs mainly during a 2 d treatment period, and additional cell death is minimal 2-11 d after treatment. Considered together, intracellular repair of partially damaged hair cells can be an important contributor to spontaneous hair cell recovery in mammalian inner ears.

Therapeutic potential of neurotrophins for treatment of hearing loss

Degeneration of spiral ganglion neurons (SGNs) and hair cells in the cochlea induced by aging, injury, ototoxic drugs, acoustic trauma, and various diseases is the major cause of hearing loss. Discovery of growth factors that can either prevent SGN and hair-cell death or stimulate hair-cell regeneration would be of great interest. Studies over the past several years have provided evidence that specific neurotrophins are potent survival factors for SGNs and protect these neurons from ototoxic drugs in vitro and in vivo. Current research focuses more on understanding the mechanism of hair-cell regeneration/differentiation and identification of growth factors that can stimulate hair-cell regeneration. SGNs are required to relay the signal to the central nervous system even when a cochlear implant is used to replace hair-cell function or in the case that cochlear sensory epithelium can be stimulated to regenerate new hair cells successfully. Therefore, neurotrophins may have their therapeutic value in prevention and treatment of hearing impairment.

Distinct expression patterns of notch family receptors and ligands during development of the mammalian inner ear

The cochlea and vestibular structures of the inner ear labyrinth develop from the otic capsule via step-wise regional and cell fate specification. Each inner ear structure contains a sensory epithelium, composed of hair cells, the mechanosensory transducers, and supporting cells. We examined the spatio-temporal expression of genes in the Notch signaling pathway, Notch receptors (Notch1-4) and two ligands, Jagged1 and Delta1, in the developing mammalian inner ear. Our results show that Notch1 and Jagged1 are first expressed in the otic vesicle, likely involved in differentiation of the VIIIth nerve ganglion neurons, and subsequently within the inner ear sensory epithelia, temporally coincident with initial hair cell differentiation. Notch1 expression is specific to hair cells and Jagged1 to supporting cells. Their expression persists into adult. Notch2, Notch3, Notch4, and Delta1 are excluded from the inner ear epithelia. These data support the hypothesis that Notch signaling is involved in hair cell differentiation during inner ear morphogenesis.

Requirement for Brn-3c in maturation and survival, but not in fate determination of inner ear hair cells

Mutations in the POU domain gene Brn-3c causes hearing impairment in both the human and mouse as a result of inner ear hair cell loss. We show here that during murine embryogenesis, Brn-3c is expressed in postmitotic cells committed to hair cell phenotype but not in mitotic progenitors in the inner ear sensory epithelium. In developing auditory and vestibular sensory epithelia of Brn-3c−/− mice, hair cells are found to be generated and undergo initial differentiation as indicated by their morphology, laminar position and expression of hair cell markers, including myosins VI and VIIa, calretinin and parvalbumin. However, a small number of hair cells are anomalously retained in the supporting cell layer in the vestibular sensory epithelia. Furthermore, the initially differentiated hair cells fail to form stereociliary bundles and degenerate by apoptosis in the Brn-3c−/− mice. These data indicate a crucial role for Brn-3c in maturation, survival and migration of hair cells, but not in proliferation or commitment of hair cell progenitors.

Regulation of hippocampal synaptic plasticity by the tyrosine kinase receptor, REK7/EphA5, and its ligand, AL-1/Ephrin-A5

The Eph-related tyrosine kinase receptor, REK7/EphA5, mediates the effects of AL-1/Ephrin-A5 and related ligands and is involved in the guidance of retinal, cortical, and hippocampal axons during development. The continued expression of REK7/EphA5 in the adult brain, in particular in areas associated with a high degree of synaptic plasticity such as the hippocampus, raises the question of its function in the mature nervous system. In this report we examined the role of REK7/EphA5 in synaptic remodeling by asking if agents that either block or activate REK7/EphA5 affect synaptic strength in hippocampal slices from adult mouse brain. We show that a REK7/EphA5 antagonist, soluble REK7/EphA5-IgG, impairs the induction of long-term potentiation (LTP) without affecting other synaptic parameters such as normal synaptic transmission or paired-pulse facilitation. In contrast, perfusion with AL-1/Ephrin-A5-IgG, an activator of REK7/EphA5, induces a sustained increase in normal synaptic transmission that partially mimics LTP. The sustained elevation of normal synaptic transmission could be attributable to a long-lasting binding of the AL-1/Ephrin-A5-IgG to the endogenous REK7/EphA5 receptor, as revealed by immunohistochemistry. Furthermore, maximal electrical induction of LTP occludes the potentiating effects of subsequent treatment with AL-1/Ephrin-A5-IgG. Taken together these results implicate REK7/EphA5 in the regulation of synaptic plasticity in the mature hippocampus and suggest that REK7/EphA5 activation is recruited in the LTP induced by tetanization.

Establishment of conditionally immortalized rat utricular epithelial cell lines using a retrovirus-mediated gene transfer technique

Supporting cells in the inner ear sensory epithelium are most likely hair cell progenitors. In an effort to establish an in vitro model system of hair cell differentiation, we developed immortalized epithelial cell lines by transferring the tsA58 allele of the SV40 large T antigen oncogene into neonatal rat utricular supporting cells using a retrovirus. The established cell lines have been stably maintained continuously for more than 25 passages and display many features similar to primary supporting cells. They grow in patches and assume a polygonal morphology. Immunocytochemical characterization of the established cell lines reveals that these cells can be labeled by epithelial cell markers, but not by fibroblast, glial or neuronal markers. The immortalized cells grow rapidly in serum medium at permissive temperature, but the majority cease proliferation when cultured in serum free medium at non-permissive temperature. These cells respond to mitogenic growth factors including bFGF, EGF and TGF-alpha and express growth factor receptors in a manner similar to the primary supporting cells. Furthermore, we find that the cells undergo a morphological differentiation when cultured in serum free medium at non-permissive temperature in the presence of bFGF. Under these conditions, the cells shrink in size, become elongated, and express early hair cell markers such as calretinin and calmodulin. The utricular epithelial cell line we have established may potentially provide an invaluable system for studying hair cell differentiation and regeneration.

Analysis of rat vestibular hair cell development and regeneration using calretinin as an early marker

Despite increased interest in inner ear hair cell regeneration, it is still unclear what exact mechanisms underlie hair cell regeneration in mammals because of our limited understanding of hair cell development and the lack of specific hair cell markers. In this report, we studied hair cell development using immunohistochemistry on sections prepared from embryonic day (E) 13 to postnatal day 7 rat inner ear tissues. Of many epithelial, neuronal, and glial markers, we found that calcium-binding protein antibodies recognizing calretinin, calmodulin, or parvalbumin labeled immature hair cells in rat vestibular end organs. In particular, calretinin antiserum labeled the initial differentiating hair cells at E15, a stage immediately after the terminal mitosis of hair cell progenitors. The selective immunoreactivity of postmitotic presumptive hair cells, but not supporting cells or peripheral epithelial cells, was confirmed in utricular epithelial sheet cultures. Double labeling with calretinin and bromodeoxyuridine antibodies in long-term cultures showed that only a few mitotic utricular supporting cells became calretinin positive. Thus, although proliferation-mediated regeneration of new hair cells might directly contribute to hair cell regeneration in rat utricles after injury, it is very limited. In addition, double labeling with calretinin and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) revealed that differentiated hair cells underwent apoptosis during normal development at late embryonic and early postnatal stages in vivo and in vitro. Therefore, these experiments lay the groundwork for the time course of differentiation, regeneration, and apoptosis of mammalian vestibular hair cells. This work also suggests that calcium-binding proteins are useful markers for studies on inner ear hair cell differentiation and regeneration.

Induction of cell proliferation by fibroblast and insulin-like growth factors in pure rat inner ear epithelial cell cultures

Proliferation of supporting cells in the inner ear is the early major event occurring during hair cell regeneration after acoustic trauma or aminoglycoside treatment. In the present study, we examined the possible influence of 30 growth factors on the proliferation of pure rat utricular epithelial cells in culture. Utricular epithelial sheets were separated and partially dissociated from early postnatal rats via a combined enzymatic and mechanical method. The cultured utricular epithelial cells expressed exclusively epithelial cell antigens, but not fibroblast, glial, or neuronal antigens. With tritiated thymidine incorporation assays, we found that several fibroblast growth factor (FGF) family members, insulin-like growth factor-1 (IGF-1), IGF-2, transforming growth factor-alpha (TGF-alpha), and epidermal growth factor (EGF), stimulated proliferation of the utricular epithelial cells. In contrast, neurotrophins and other growth factors did not elicit any detectable mitogenic effects. Among all of the growth factors examined, FGF-2 was the most potent mitogen. When FGF-2 was added in combination with IGF-1 or TGF-alpha to the medium, combined effects were seen. These results were confirmed with BrdU immunocytochemistry. Thus, the present culture system provides a rapid and reliable assay system to screen novel growth factors involved in proliferation of mammalian inner ear supporting cells. Furthermore, immunostainings revealed that the cultured utricular epithelial cells expressed FGF and IGF-1 receptors, and utricular hair cells produced FGF-2 in vivo. The addition of neutralizing antibodies against FGF-2 or IGF-1 to the cultures significantly inhibited the utricular epithelial cell proliferation. This work suggests that FGF-2 and IGF-1 may regulate the proliferation step during hair cell development and regeneration.

Multiple factors control the proliferation and differentiation of rat early embryonic (day 9) neuroepithelial cells

The proliferation and differentiation of neural precursor cells is largely controlled by environmental factors. By providing the factors that favor the proliferation or suppress the differentiation of this cell type, we isolated and expanded an early neuroepithelial pre-differentiated cell type from E9 rat neural plate in serum-free medium. This has led to the establishment of a neural epithelial precursor (NEP) cell line. The NEP cell's properties are substantially different from those of cell lines previously derived from neural tissue at later stages of development. Initial selection and survival of this cell type requires a factor secreted by an embryonic Schwann (nrESC) cell line. Continued passage of these cells requires cell-cell contact for both survival and growth. Neural cell differentiation can be induced in this nestin positive precursor cell line by bFGF and forskolin. General neuronal markers, as well as cortical neuron-specific protein kinase C isozyme, and accumulation of glutamate and aspartate were induced in most cells. Choline acetyl-transferase was also induced in a small number of cells. When implanted into neonatal rat brain, the NEP cell line gave rise to several distinct neuronal and glial phenotypes in different regions of the brain including cerebellar cortex and hippocampus.

Differential damage to auditory neurons and hair cells by ototoxins and neuroprotection by specific neurotrophins in rat cochlear organotypic cultures

Therapeutic ototoxic drugs are one of the major causes of damage in the peripheral auditory system, leading to hearing loss. In this study, we have examined the toxic actions of three classes of ototoxins (sodium salicylate, gentamicin and cisplatin) in organotypic cultures of postnatal cochlear explants. In these cultures, afferent innervation of hair cells by primary auditory neurons remained intact. Double labelling with a monoclonal antibody against neurofilament protein and a phalloidin-fluorescein isothiocyanate conjugate revealed that the three types of drugs induced differential damage to auditory neurons and hair cells in the cochlea. While gentamicin preferentially caused hair cell death, sodium salicylate specifically induced degeneration of auditory neurons. In contrast, cisplatin resulted in destruction of both auditory neurons and hair cells. Neuronal degeneration was largely prevented by the addition of neurotrophin-4/5, brain-derived neurotrophic factor and neurotrophin-3 to the culture media together with the ototoxins, while nerve growth factor and other growth factors had no effect. In contrast, the hair cell loss caused by cisplatin or gentamicin was not attenuated by the presence of neurotrophins. These results suggest that ototoxic mechanisms of salicylates, aminoglycosides and chemotherapeutic agents are different. Auditory neuronal loss induced by ototoxins may be prevented by specific neurotrophins.

Neurotrophin-4/5, brain-derived neurotrophic factor, and neurotrophin-3 promote survival of cultured vestibular ganglion neurons and protect them against neurotoxicity of ototoxins

The ability of neurotrophin-4/5 (NT-4/5), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and nerve growth factor (NGF) to promote survival of postnatal rat vestibular ganglion neurons (VGNs) was examined in dissociated cell cultures. Of the four neurotrophins, NT-4/5 and BDNF were equally effective but more potent than NT-3 in promoting the survival of VGNs. In contrast, NGF showed no detectable effects. As expected, TrkB-IgG (a fusion protein of extracellular domain of TrkB and Fc domain of human immunoglobulin G) specifically inhibited the survival-promoting, effects by NT-4/5 or BDNF and TrkC-IgG fusion protein completely blocked that of NT-3. Immunohistochemistry with TrkB, TrkA, and p75 antisera revealed that VGNs made TrkB and p75 proteins, but not TrkA protein. Ototoxic therapeutic drugs such as cisplatin and gentamicin often induce degeneration of hair cells and ganglion neurons in both auditory and vestibular systems that leads to impairment of hearing and balance. When cisplatin and gentamicin were added to the dissociated VGN culture in which the hair cells were absent, additional cell death of VGNs was induced, suggesting that the two ototoxins may have a direct neurotoxic effect on ganglion neurons in addition to their known toxicity on hair cells. However, if the cultures were co-treated with neurotrophins, NT-4/5, BDNF, and NT-3, but not NGF, prevented or reduced the neurotoxicity of the two ototoxins. Thus, the three neurotrophins are survival factors for VGNs and are implicated in the therapeutic prevention of VGN loss caused by injury and ototoxins.

Neurotrophin-4/5 enhances survival of cultured spiral ganglion neurons and protects them from cisplatin neurotoxicity

Destruction of spiral ganglion neurons (SGNs) induced by injury and toxins is one of the major causes for hearing loss. Here we report that neurotrophin-4/5 (NT-4/5), a member of the nerve growth factor family, promoted survival of postnatal rat SGNs up to threefold in dissociated cell cultures. The survival-promoting potency of NT-4/5 was equivalent to that of BDNF and stronger than that of NT-3. In contrast, NGF showed no detectable effects. Immunohistochemistry, with TrkB and TrkA antisera, revealed that these neurons produced TrkB protein, the functional receptor for NT-4/5 and BDNF, but not TrkA protein, the high-affinity receptor for NGF. The survival-promoting activity of NT-4/5 was completely inhibited by TrkB-IgG fusion protein. These results suggest that NT-4/5 is a specific survival factor for SGNs. In addition, NT-4/5 protected the SGNs from neurotoxic effects of the anti-cancer drug, cisplatin. Thus, NT-4/5 may have therapeutic value in preventing hearing impairment caused by damage to primary auditory afferent neurons.

Neurotrophin-3 reverses experimental cisplatin-induced peripheral sensory neuropathy

Cisplatin, a widely used chemotherapeutic agent, induces a sensory neuropathy with selective loss of vibration sense and proprioception. Here we demonstrate that neurotrophin-3 (NT-3), a member of the nerve growth factor family of neurotrophic factors, restored to normal levels the reduced H-reflex-related sensory nerve conduction velocity induced by cisplatin in rats. NT-3 treatment corrected an abnormal cytoplasmic distribution of neurofilament protein in large sensory neurons in dorsal root ganglia and the reduction in the numbers of myelinated fibers in sural nerves caused by cisplatin. The NT-3-dependent reversal of cisplatin neurotoxicity thus suggests the possible use of NT-3 in the treatment of peripheral sensory neuropathy.

Neurotrophin-4/5 (NT-4/5) and brain-derived neurotrophic factor (BDNF) act at later stages of cerebellar granule cell differentiation

The developing cerebellum expresses genes which encode for both neurotrophins and their receptors. The present study was designed to determine at what stages during cerebellar granule cell neurogenesis neurotrophin family molecules may act. We report here that in purified, well-characterized granule cell cultures (Gao et al., 1991; 1992), none of the neurotrophins stimulated proliferation of granule cell precursors or rescued phenotypic defect of mutant weaver granule cell precursors in the initiation of neuronal differentiation. However, neurotrophin-4/5 (NT-4/5) and BDNF, but not neurotrophin-3 (NT-3) or NGF, promoted neurite extension and survival of differentiated cerebellar granule cells. Both of these effects were blocked by the specific inhibitor for Trk tyrosine kinases, K-252a. NT-4/5 and BDNF also enhanced neurite extension by weaver granule cells which were rescued by wild-type granule cells during differentiation. Moreover, TrkB immunohistochemistry performed on sections of the developing wildtype and weaver cerebella revealed that only differentiated granule cells, but not the precursor cells, make high levels of TrkB receptor. These findings together suggest that NT-4/5 and BDNF promote the maturation and maintenance of differentiated granule cells, effects which are downstream to the weaver gene. Since no additive effects were seen with the combination of NT-4/5 and BDNF, it seems likely that the two neurotrophins activate the same receptor trkB for signal transduction.

Immortalizing oncogenes subvert the establishment of granule cell identity in developing cerebellum

After implantation into the external germinal layer of early postnatal cerebellum, primary external germinal layer progenitor cells gave rise exclusively to granule neurons. In contrast, all major classes of cerebellar cells were observed following implantation of embryonic day 13 cerebellar precursor cells into the external germinal layer. These results suggest that granule cells arise from precursors with a restricted potential. In contrast to results with the primary external germinal layer population, cell lines established from external germinal layer cells, by infection with a retrovirus containing the SV40 large T-antigen oncogene, gave rise to several cerebellar cell types upon implantation. These included granule neurons, one subclass of stellate interneurons, Golgi cells, Bergmann glia and astrocytes. From these results, we conclude that early postnatal external germinal layer progenitors are normally fated to a granule cell identity and that expression of the SV40 large T-antigen oncogene subverts mechanisms that control granule neuron fate.

Growth cone "collapse" in vivo: are inhibitory interactions mediated by gap junctions?

In the leech embryo, oppositely directed axons of homologous anterior pagoda (AP) neurons overlap with each other extensively within the nerves that link adjacent ganglia, and inhibit each other's further growth (Gao and Macagno, 1987b). During this 5-8 d period of inhibition, the axons begin to grow thin, and eventually they retract completely. However, deletion of one overlapping AP cell results in the renewed growth of the remaining AP cell's axon, which then innervates territory vacated by the killed cell. Thus, each neuron can detect the presence of the other, and adjust its branching pattern accordingly. To begin to explore how these neurons detect and inhibit each other, we tested for direct communication between them. Dye fills with fluorescent chromophores suggested direct contact between their axons at the light level, and this was confirmed by serial-section electron microscopic analysis. Morphological features resembling aspects of gap junctions were observed where the projections were closely apposed, and subsequent electrophysiological recordings demonstrated electrical coupling between the mutually inhibited axons. Confirmation that these projections communicate via gap junctions was obtained using intracellular injection of 5-HT as a tracer, followed by anti-5-HT immunohistochemistry. The tracer passed selectively between AP neurons. We propose that the gap junctions formed between the transient projections of the developing AP neurons may mediate the exchange of the signals that permit homologs to recognize each other and to inhibit the further forward progress of these projections.

Neuronal differentiation rescued by implantation of Weaver granule cell precursors into wild-type cerebellar cortex

The migration of postmitotic neurons away from compact, germinal zones is a critical step in neuronal differentiation in the developing brain. To study the molecular signals necessary for cerebellar granule cell migration in situ, precursor cells from the neurological mutant mouse weaver, an animal with phenotypic defects in migration, were implanted into the external germinal layer (EGL) of wild-type cerebellar cortex. In this region, labeled weaver precursor cells of the EGL progressed through all stages of granule neuron differentiation, including the extension of parallel fibers, migration through the molecular and Purkinje cell layers, positioning in the internal granule cell layer, and extension of dendrites. Thus, the weaver gene acts nonautonomously in vivo, and local cell interactions may induce early steps in neuronal differentiation that are required for granule cell migration.

The weaver gene encodes a nonautonomous signal for CNS neuronal differentiation

In the neurological mutant mouse weaver, CNS precursor cells in the external germinal layer (EGL) of the cerebellar cortex proliferate normally, but fail to differentiate and die in the proliferative zone. To examine the autonomy of expression of the weaver gene, we carried out cell-mixing experiments in vitro. In homotypic, reaggregate cultures, weaver EGL precursor cells expressed the general neuronal markers N-CAM, L1, and MAP2, but failed to express the late neuronal antigens TAG-1 and astrotactin, to extend neurites or to migrate on glial fibers. After reaggregation with wild-type EGL precursor cells, weaver precursor cells extended neurites equivalent in length to wild-type cells, migrated along astroglial fibers, and expressed TAG-1 and astrotactin. Rescue of neurite production was also achieved by the addition of membranes from, but not by medium conditioned by wild-type cells. These findings suggest that the weaver gene acts non-autonomously, encoding a membrane-associated ligand that induces EGL neuronal differentiation.

Segmental differentiation in the leech central nervous system: proposed segmental homologs of the heart accessory neurons

As part of an on-going study of segmental differentiation in the central nervous system (CNS) of the leech Hirudo medicinalis, a search was made for putative segmental homologs of the heart accessory (HA) neurons, which exist exclusively as a bilateral pair in the ganglia of the fifth and sixth body segments. As it is not yet feasible to obtain adequate cell lineage information in H. medicinalis, potential homologs of the HA neurons were determined using morphological, immunohistochemical, and electrophysiological criteria. Among cells in other body ganglia with somata in the same locations as HA neurons, a pair was found having extensive morphological and physiological similarities to HA neurons. These we have called HA-like (HAL) neurons. Adult HA and HAL neurons have closely related patterns of primary branching, in terms of shape, intraganglionic pathways taken, and extraganglionic projections. The number, location, and relative thickness of branches are also similar among these cells. In embryos 10 to 11 days old, HA and HAL neurons have virtually identical branching patterns, with primary and secondary branches of nearly uniform caliber. Differences in branch thickness develop gradually; by embryonic day 20, they resemble those found in adult neurons. Two features found to differ between HA and HAL neurons were the cell body diameter (larger for the HA cells) and the expression of antigens recognized by the monoclonal antibody Laz1-1 (absent at a detectable level in the HA neurons). At a physiological level, the HA and HAL neurons showed action potentials of similar size and shape, as well as inhibitory synaptic inputs from a common source, the heart interneurons (HN). The observations presented here suggest that there is a common developmental origin for the HA and HAL neurons, and hence that their fates are positionally determined by as yet unknown factors.

Competition or inhibition? Developmental strategies in the establishment of peripheral projections by leech neurons

Leech neurons, like those of other invertebrates and those of vertebrates, undergo specific interactions during development which serve to define their adult morphologies and synaptic connections. We review here several observations and experiments that illustrate these interactions. In particular, we consider how they shape and constrain peripheral arborizations and whether the evidence favors competition or inhibition as their mode of action.

Axon extension and retraction by leech neurons: severing early projections to peripheral targets prevents normal retraction of other projections

During leech embryogenesis, interactions between homologous neurons in neighboring segments lead to the selective retraction of longitudinal axonal projections by midbody AP and AE neurons, which maintain lateral axonal projections to the periphery. Results of experiments reported here show that disconnecting the lateral projections from the periphery rescues the projections normally fated to retract. We propose that these neurons normally progress through two states during early development, one in which they are insensitive to interactions with their homologs (state A) and a second in which they are sensitive (state B). Establishment of lateral connections with their targets triggers the switch from state A to state B; cutting these projections puts neurons back to state A.

Cell death during gangliogenesis in the leech: bipolar cells appear and then degenerate in all ganglia

The bipolar cells can be recognized very early during gangliogenesis in the leech central nervous system by their expression of antigens that are recognized by the monoclonal antibody Laz1-1. They are the first cells to express these antigens, which are later shared with a distinct set of other cells in the leech nervous system. Their processes extend several segments rostrally and caudally along the forming interganglionic connective nerves; they are first found in anterior segments and gradually appear in more posterior ones over the course of 2-3 d. At about the time bipolar cells appear in the neuromeres of the tail ganglion, those in the most anterior segmental ganglia begin to degenerate. Degeneration proceeds caudally over the next 3 d, until all bipolar cells have disappeared. Bipolar cells are, thus, members of that class of cells that exists for only a short period in neurogenesis and then presumably disappears once its functions are no longer required. These cells' morphology and appearance at the earliest stages in the formation of the interganglionic connective nerves are suggestive of a role in the establishment of these longitudinal pathways in the leech CNS.

Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. II. The AP and AE neurons

To assess the generality of our previous finding (Gao and Macagno, 1987) that segmental homologues play a role in the establishment of the pattern of axonal projections of the heart accessory HA neurons, we have extended our studies to two other identified leech neurons: the anterior pagoda (AP) neurons and the annulus erector (AE) motor neurons. Bilateral pairs of AP neurons are found in the first through the twentieth segmental ganglia (SG1 through SG20) of the leech ventral nerve cord. All AP neurons initially extend axonal projections to the contralateral periphery as well as longitudinal projections along the contralateral interganglionic connective nerves toward anterior and posterior neighboring ganglia. Although the peripheral projections are maintained by all AP neurons throughout the life of the animal, the longitudinal projections disappear in all but two segments: the AP neurons in SG1 maintain their anterior projections and extend them into the head ganglion, and those in SG20 maintain their posterior projections and extend them into SG21 and the tail ganglion. When single AP neurons are deleted anywhere along the nerve cord before processes begin to atrophy, however, the longitudinal projections are retained by their ipsilateral homologues in adjacent ganglia. The rescued processes appear to take over the projections of the deleted neurons. In cases where two or more AP neurons on the same side of the nerve cord are deleted from adjacent ganglia, a contralateral homologue sometimes extends projections to the periphery ipsilaterally or on both sides. We obtained similar results when we deleted single AE neurons from midbody ganglia. Thus, our experiments with three different identified neurons consistently show that the initial pattern of projections is the same in all ganglia, but that the existence of homologues in adjacent ganglia leads to the pruning of some of the initial projections. A consequence of this homologue-dependent process retraction is that neurons normally lacking neighboring homologues will have patterns of projections different from those neurons that do have such neighbors. Process loss by the HA, AP, and AE neurons may be the result either of competition for targets, inputs, or growth factors or of direct interactions among homologous cells.

Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. I. The HA cells

The role of homologues in the establishment of the pattern of axonal projections of identified segmentally homologous neurons was investigated by means of selective cell ablation and dye injection. The cells studied were the bilateral pairs of heart accessory (HA) neurons found in the fifth and sixth segmental ganglia of the leech ventral nerve cord. Homologues start their morphological differentiation with identical axonal projections, and segmental differences are manifested later, when specific branches stop growing and disappear. The deletion of single HA cells at early stages, however, permits these branches to survive in their ipsilateral homologues and to grow and take over the projections of the deleted neurons. In addition, if both HA homologues on the same side of the nerve cord, or three of the four HA cells, are deleted in an animal, the remaining HA cells often extend novel projections. These observations suggest that either competition for targets, inputs or growth factors, or direct interactions among homologous cells may play a role in the differentiation of segment specific patterns of axonal projections.