Devising a framework of optogenetic coding in the auditory pathway: Insights from auditory midbrain recordings

Cochlear implants (CIs) restore activity in the deafened auditory system via electrical stimulation of the auditory nerve. As the spread of electric current in biological tissues is rather broad, the spectral information provided by electrical CIs is limited. Optogenetic stimulation of the auditory nerve has been suggested for artificial sound coding with improved spectral selectivity, as light can be conveniently confined in space. Yet, the foundations for optogenetic sound coding strategies remain to be established. Here, we parametrized stimulus-response-relationships of the auditory pathway in gerbils for optogenetic stimulation. Upon activation of the auditory pathway by waveguide-based optogenetic stimulation of the spiral ganglion, we recorded neuronal activity of the auditory midbrain, in which neural representations of spectral, temporal, and intensity information can be found. Screening a wide range of optical stimuli and taking the properties of optical CI emitters into account, we aimed to optimize stimulus paradigms for potent and energy-efficient activation of the auditory pathway. We report that efficient optogenetic coding builds on neural integration of millisecond stimuli built from microsecond light pulses, which optimally accommodate power-efficient laser diode operation. Moreover, we performed an activity-level-dependent comparison of optogenetic and acoustic stimulation in order to estimate the dynamic range and the maximal stimulation intensity amenable to single channel optogenetic sound encoding, and indicate that it complies well with speech comprehension in a typical conversation (65 dB). Our results provide a first framework for the development of coding strategies for future optogenetic hearing restoration.

Group-based, autonomous, individualized training and testing of long-tailed macaques (Macaca fascicularis) in their home enclosure to a visuo-acoustic discrimination task

In recent years, the utility and efficiency of automated procedures for cognitive assessment in psychology and neuroscience have been demonstrated in non-human primates (NHP). This approach mimics conventional shaping principles of breaking down a final desired behavior into smaller components that can be trained in a staircase manner. When combined with home-cage-based approaches, this could lead to a reduction in human workload, enhancement in data quality, and improvement in animal welfare. However, to our knowledge, there are no reported attempts to develop automated training and testing protocols for long-tailed macaques (Macaca fascicularis), a ubiquitous NHP model in neuroscience and pharmaceutical research. In the current work, we present the results from 6 long-tailed macaques that were trained using an automated unsupervised training (AUT) protocol for introducing the animals to the basics of a two-alternative choice (2 AC) task where they had to discriminate a conspecific vocalization from a pure tone relying on images presented on a touchscreen to report their response. We found that animals (1) consistently engaged with the device across several months; (2) interacted in bouts of high engagement; (3) alternated peacefully to interact with the device; and (4) smoothly ascended from step to step in the visually guided section of the procedure, in line with previous results from other NHPs. However, we also found (5) that animals' performance remained at chance level as soon as the acoustically guided steps were reached; and (6) that the engagement level decreased significantly with decreasing performance during the transition from visual to acoustic-guided sections. We conclude that with an autonomous approach, it is possible to train long-tailed macaques in their social group using computer vision techniques and without dietary restriction to solve a visually guided discrimination task but not an acoustically guided task. We provide suggestions on what future attempts could take into consideration to instruct acoustically guided discrimination tasks successfully.

Flexible auditory training, psychophysics, and enrichment of common marmosets with an automated, touchscreen-based system

Devising new and more efficient protocols to analyze the phenotypes of non-human primates, as well as their complex nervous systems, is rapidly becoming of paramount importance. This is because with genome-editing techniques, recently adopted to non-human primates, new animal models for fundamental and translational research have been established. One aspect in particular, namely cognitive hearing, has been difficult to assess compared to visual cognition. To address this, we devised autonomous, standardized, and unsupervised training and testing of auditory capabilities of common marmosets with a cage-based standalone, wireless system. All marmosets tested voluntarily operated the device on a daily basis and went from naïve to experienced at their own pace and with ease. Through a series of experiments, here we show, that animals autonomously learn to associate sounds with images; to flexibly discriminate sounds, and to detect sounds of varying loudness. The developed platform and training principles combine in-cage training of common marmosets for cognitive and psychoacoustic assessment with an enriched environment that does not rely on dietary restriction or social separation, in compliance with the 3Rs principle.

The authors present a cage-based stand-alone platform for autonomous, standardized, and unsupervised training and testing of visuo-auditory-cued behaviours of common marmosets. The experiments do not require dietary restriction or social separation.

Effects of Cortical Cooling on Sound Processing in Auditory Cortex and Thalamus of Awake Marmosets

The auditory thalamus is the central nexus of bottom-up connections from the inferior colliculus and top-down connections from auditory cortical areas. While considerable efforts have been made to investigate feedforward processing of sounds in the auditory thalamus (medial geniculate body, MGB) of non-human primates, little is known about the role of corticofugal feedback in the MGB of awake non-human primates. Therefore, we developed a small, repositionable cooling probe to manipulate corticofugal feedback and studied neural responses in both auditory cortex and thalamus to sounds under conditions of normal and reduced cortical temperature. Cooling-induced increases in the width of extracellularly recorded spikes in auditory cortex were observed over the distance of several hundred micrometers away from the cooling probe. Cortical neurons displayed reduction in both spontaneous and stimulus driven firing rates with decreased cortical temperatures. In thalamus, cortical cooling led to increased spontaneous firing and either increased or decreased stimulus driven activity. Furthermore, response tuning to modulation frequencies of temporally modulated sounds and spatial tuning to sound source location could be altered (increased or decreased) by cortical cooling. Specifically, best modulation frequencies of individual MGB neurons could shift either toward higher or lower frequencies based on the vector strength or the firing rate. The tuning of MGB neurons for spatial location could both sharpen or widen. Elevation preference could shift toward higher or lower elevations and azimuth tuning could move toward ipsilateral or contralateral locations. Such bidirectional changes were observed in many parameters which suggests that the auditory thalamus acts as a filter that could be adjusted according to behaviorally driven signals from auditory cortex. Future work will have to delineate the circuit elements responsible for the observed effects.

Laser-Induced Apoptosis of Corticothalamic Neurons in Layer VI of Auditory Cortex Impact on Cortical Frequency Processing

Corticofugal projections outnumber subcortical input projections by far. However, the specific role for signal processing of corticofugal feedback is still less well understood in comparisonto the feedforward projection. Here, we lesioned corticothalamic (CT) neurons in layers V and/or VI of the auditory cortex of Mongolian gerbils by laser-induced photolysis to investigate their contribution to cortical activation patterns. We have used laminar current-source density (CSD) recordings of tone-evoked responses and could show that, particularly, lesion of CT neurons in layer VI affected cortical frequency processing. Specifically, we found a decreased gain of best-frequency input in thalamocortical (TC)-recipient input layers that correlated with the relative lesion of layer VI neurons, but not layer V neurons. Using cortical silencing with the GABA _a -agonist muscimol and layer-specific intracortical microstimulation (ICMS), we found that direct activation of infragranular layers recruited a local recurrent cortico-thalamo-cortical loop of synaptic input. This recurrent feedback was also only interrupted when lesioning layer VI neurons, but not cells in layer V. Our study thereby shows distinct roles of these two types of CT neurons suggesting a particular impact of CT feedback from layer VI to affect the local feedforward frequency processing in auditory cortex.

Multichannel optogenetic stimulation of the auditory pathway using microfabricated LED cochlear implants in rodents

When hearing fails, electrical cochlear implants (eCIs) provide the brain with auditory information. One important bottleneck of CIs is the poor spectral selectivity that results from the wide current spread from each of the electrode contacts. Optical CIs (oCIs) promise to make better use of the tonotopic order of spiral ganglion neurons (SGNs) inside the cochlea by spatially confined stimulation. Here, we established multichannel oCIs based on light-emitting diode (LED) arrays and used them for optical stimulation of channelrhodopsin (ChR)-expressing SGNs in rodents. Power-efficient blue LED chips were integrated onto microfabricated 15-μm-thin polyimide-based carriers comprising interconnecting lines to address individual LEDs by a stationary or mobile driver circuitry. We extensively characterized the optoelectronic, thermal, and mechanical properties of the oCIs and demonstrated stability over weeks in vitro. We then implanted the oCIs into ChR-expressing rats and gerbils, and characterized multichannel optogenetic SGN stimulation by electrophysiological and behavioral experiments. Improved spectral selectivity was directly demonstrated by recordings from the auditory midbrain. Long-term experiments in deafened ChR-expressing rats and in nontreated control animals demonstrated specificity of optogenetic stimulation. Behavioral studies on animals carrying a wireless oCI sound processor revealed auditory percepts. This study demonstrates hearing restoration with improved spectral selectivity by an LED-based multichannel oCI system.

Acute and Long-Term Circuit-Level Effects in the Auditory Cortex After Sound Trauma

Harmful environmental sounds are a prevailing source of chronic hearing impairments, including noise induced hearing loss, hyperacusis, or tinnitus. How these symptoms are related to pathophysiological damage to the sensory receptor epithelia and its effects along the auditory pathway, have been documented in numerous studies. An open question concerns the temporal evolution of maladaptive changes after damage and their manifestation in the balance of thalamocortical and corticocortical input to the auditory cortex (ACx). To address these issues, we investigated the loci of plastic reorganizations across the tonotopic axis of the auditory cortex of male Mongolian gerbils (Meriones unguiculatus) acutely after a sound trauma and after several weeks. We used a residual current-source density analysis to dissociate adaptations of intracolumnar input and horizontally relayed corticocortical input to synaptic populations across cortical layers in ACx. A pure tone-based sound trauma caused acute changes of subcortical inputs and corticocortical inputs at all tonotopic regions, particularly showing a broad reduction of tone-evoked inputs at tonotopic regions around the trauma frequency. At other cortical sites, the overall columnar activity acutely decreased, while relative contributions of lateral corticocortical inputs increased. After 4-6 weeks, cortical activity in response to the altered sensory inputs showed a general increase of local thalamocortical input reaching levels higher than before the trauma. Hence, our results suggest a detailed mechanism for overcompensation of altered frequency input in the auditory cortex that relies on a changing balance of thalamocortical and intracortical input and along the frequency gradient of the cortical tonotopic map.

μLED-based optical cochlear implants for spectrally selective activation of the auditory nerve

Electrical cochlear implants (eCIs) partially restore hearing and enable speech comprehension to more than half a million users, thereby re-connecting deaf patients to the auditory scene surrounding them. Yet, eCIs suffer from limited spectral selectivity, resulting from current spread around each electrode contact and causing poor speech recognition in the presence of background noise. Optogenetic stimulation of the auditory nerve might overcome this limitation as light can be conveniently confined in space. Here, we combined virus-mediated optogenetic manipulation of cochlear spiral ganglion neurons (SGNs) and microsystems engineering to establish acute multi-channel optical cochlear implant (oCI) stimulation in adult Mongolian gerbils. oCIs based on 16 microscale thin-film light-emitting diodes (μLEDs) evoked tonotopic activation of the auditory pathway with high spectral selectivity and modest power requirements in hearing and deaf gerbils. These results prove the feasibility of μLED-based oCIs for spectrally selective activation of the auditory nerve.

Emerging approaches for restoration of hearing and vision

Impairments of vision and hearing are highly prevalent conditions limiting the quality of life and presenting a major socioeconomic burden. For long, retinal and cochlear disorders have remained intractable for causal therapies, with sensory rehabilitation limited to glasses, hearing aids, and electrical cochlear or retinal implants. Recently, the application of gene therapy and optogenetics to eye and ear has generated hope for a fundamental improvement of vision and hearing restoration. To date, one gene therapy for the restoration of vision has been approved and undergoing clinical trials will broaden its application including gene replacement, genome editing, and regenerative approaches. Moreover, optogenetics, i.e. controlling the activity of cells by light, offers a more general alternative strategy. Over little more than a decade, optogenetic approaches have been developed and applied to better understand the function of biological systems, while protein engineers have identified and designed new opsin variants with desired physiological features. Considering potential clinical applications of optogenetics, the spotlight is on the sensory systems. Multiple efforts have been undertaken to restore lost or hampered function in eye and ear. Optogenetic stimulation promises to overcome fundamental shortcomings of electrical stimulation, namely poor spatial resolution and cellular specificity, and accordingly to deliver more detailed sensory information. This review aims at providing a comprehensive reference on current gene therapeutic and optogenetic research relevant to the restoration of hearing and vision. We will introduce gene-therapeutic approaches and discuss the biotechnological and optoelectronic aspects of optogenetic hearing and vision restoration.

Optogenetic stimulation of cochlear neurons activates the auditory pathway and restores auditory-driven behavior in deaf adult gerbils

Cochlear implants partially restore hearing via direct electrical stimulation of spiral ganglion neurons (SGNs). However, spread of excitation from each electrode limits spectral coding. We explored the use of optogenetics to deliver spatially restricted and cell-specific excitation in the cochlea of adult Mongolian gerbils. Adeno-associated virus carrying the gene encoding the light-sensitive calcium translocating channelrhodopsin (CatCh) was injected into the cochlea of adult gerbils. SGNs in all cochlea turns showed stable and long-lasting CatCh expression, and electrophysiological recording from single SGNs showed that light stimulation up to few hundred Hertz induced neuronal firing. We characterized the light-induced activity in the auditory pathway by electrophysiological and behavioral analysis. Light- and sound-induced auditory brainstem responses showed similar kinetics and amplitude. In normal hearing adult gerbils, optical cochlear implants elicited stable optical auditory brainstem responses over a period of weeks. In normal hearing animals, light stimulation cued avoidance behavior that could be reproduced by subsequent acoustic stimulation, suggesting similar perception of light and acoustic stimuli. Neurons of the primary auditory cortex of normal hearing adult gerbils responded with changes in firing rates with increasing light intensity. In deaf adult gerbils, light stimulation generated auditory responses and cued avoidance behavior indicating partial restoration of auditory function. Our data show that optogenetic cochlear stimulation achieved good temporal fidelity with low light intensities in an adult rodent model, suggesting that optogenetics might be used to develop cochlear implants with improved restorative capabilities.

Comodulation masking release in the inferior colliculus by combined signal enhancement and masker reduction

Auditory signals that contain coherent level fluctuations of a masker in different frequency regions enhance the detectability of an embedded sinusoidal target signal, an effect commonly known as comodulation masking release (CMR). Neural correlates have been proposed at different stages of the auditory system. While later stages seem to suppress the response to the masker, earlier stages are more likely to enhance their response to the signal when the masker is comodulated. Using a flanking band masking paradigm, the present study investigates how CMR is represented at the level of the inferior colliculus of the Mongolian gerbil. The responses to a target signal at various sound pressure levels in three different masking conditions were compared. In one condition the masker was a 10-Hz amplitude modulated sinusoid centered at the signal frequency while in the other two conditions six off-frequency carriers (flanking bands) were added. From 81 units 26 showed a change that enhanced the detectability of the signal if the temporal modulation of the added flanking bands was identical to that of the masker at the signal frequency compared to the other two masking conditions. This study shows that the response characteristics of these neurons represent an intermediate stage between the representation in the cochlear nucleus and the auditory cortex. This means that the response is increased during the signal intervals but is also decreased for the following masker portions.

Noise Trauma Induced Neural Plasticity Throughout the Auditory System of Mongolian Gerbils: Differences between Tinnitus Developing and Non-Developing Animals

In this study, we describe differences between neural plasticity in auditory cortex (AC) of animals that developed subjective tinnitus (group T) after noise-induced hearing loss (NIHL) compared to those that did not [group non-tinnitus (NT)]. To this end, our analysis focuses on the input activity of cortical neurons based on the temporal and spectral analysis of local field potential (LFP) recordings and an in-depth analysis of auditory brainstem responses (ABR) in the same animals. In response to NIHL in NT animals we find a significant general reduction in overall cortical activity and spectral power as well as changes in all ABR wave amplitudes as a function of loudness. In contrast, T-animals show no significant change in overall cortical activity as assessed by root mean square analysis of LFP amplitudes, but a specific increase in LFP spectral power and in the amplitude of ABR wave V reflecting activity in the inferior colliculus (IC). Based on these results, we put forward a refined model of tinnitus prevention after NIHL that acts via a top-down global (i.e., frequency-unspecific) inhibition reducing overall neuronal activity in AC and IC, thereby counteracting NIHL-induced bottom-up frequency-specific neuroplasticity suggested in current models of tinnitus development.

Considering optogenetic stimulation for cochlear implants

Electrical cochlear implants are by far the most successful neuroprostheses and have been implanted in over 300,000 people worldwide. Cochlear implants enable open speech comprehension in most patients but are limited in providing music appreciation and speech understanding in noisy environments. This is generally considered to be due to low frequency resolution as a consequence of wide current spread from stimulation contacts. Accordingly, the number of independently usable stimulation channels is limited to less than a dozen. As light can be conveniently focused, optical stimulation might provide an alternative approach to cochlear implants with increased number of independent stimulation channels. Here, we focus on summarizing recent work on optogenetic stimulation as one way to develop optical cochlear implants. We conclude that proof of principle has been presented for optogenetic stimulation of the cochlea and central auditory neurons in rodents as well as for the technical realization of flexible μLED-based multichannel cochlear implants. Still, much remains to be done in order to advance the technique for auditory research and even more for eventual clinical translation. This article is part of a Special Issue entitled <Lasker Award>.

Optogenetic stimulation of the auditory nerve

Direct electrical stimulation of spiral ganglion neurons (SGNs) by cochlear implants (CIs) enables open speech comprehension in the majority of implanted deaf subjects(1-) (6). Nonetheless, sound coding with current CIs has poor frequency and intensity resolution due to broad current spread from each electrode contact activating a large number of SGNs along the tonotopic axis of the cochlea(7-) (9). Optical stimulation is proposed as an alternative to electrical stimulation that promises spatially more confined activation of SGNs and, hence, higher frequency resolution of coding. In recent years, direct infrared illumination of the cochlea has been used to evoke responses in the auditory nerve(10). Nevertheless it requires higher energies than electrical stimulation(10,11) and uncertainty remains as to the underlying mechanism(12). Here we describe a method based on optogenetics to stimulate SGNs with low intensity blue light, using transgenic mice with neuronal expression of channelrhodopsin 2 (ChR2)(13) or virus-mediated expression of the ChR2-variant CatCh(14). We used micro-light emitting diodes (µLEDs) and fiber-coupled lasers to stimulate ChR2-expressing SGNs through a small artificial opening (cochleostomy) or the round window. We assayed the responses by scalp recordings of light-evoked potentials (optogenetic auditory brainstem response: oABR) or by microelectrode recordings from the auditory pathway and compared them with acoustic and electrical stimulation.

Optogenetic stimulation of the auditory pathway

Auditory prostheses can partially restore speech comprehension when hearing fails. Sound coding with current prostheses is based on electrical stimulation of auditory neurons and has limited frequency resolution due to broad current spread within the cochlea. In contrast, optical stimulation can be spatially confined, which may improve frequency resolution. Here, we used animal models to characterize optogenetic stimulation, which is the optical stimulation of neurons genetically engineered to express the light-gated ion channel channelrhodopsin-2 (ChR2). Optogenetic stimulation of spiral ganglion neurons (SGNs) activated the auditory pathway, as demonstrated by recordings of single neuron and neuronal population responses. Furthermore, optogenetic stimulation of SGNs restored auditory activity in deaf mice. Approximation of the spatial spread of cochlear excitation by recording local field potentials (LFPs) in the inferior colliculus in response to suprathreshold optical, acoustic, and electrical stimuli indicated that optogenetic stimulation achieves better frequency resolution than monopolar electrical stimulation. Virus-mediated expression of a ChR2 variant with greater light sensitivity in SGNs reduced the amount of light required for responses and allowed neuronal spiking following stimulation up to 60 Hz. Our study demonstrates a strategy for optogenetic stimulation of the auditory pathway in rodents and lays the groundwork for future applications of cochlear optogenetics in auditory research and prosthetics.

Human EEG very high frequency oscillations reflect the number of matches with a template in auditory short-term memory

Auditory perception comprises bottom-up as well as top-down processes. While research in the past has revealed many neural correlates of bottom-up processes, less is known about top-down modulation. Memory processes have recently been associated with oscillations in the gamma-band of human EEG (30 Hz and above) which are enhanced when incoming information matches a stored memory template. Therefore, we investigated event-related potentials (ERPs) and gamma-band activity in 17 healthy participants in a Go/NoGo-task. They listened to four frequency-modulated (FM) sounds which varied regarding the frequency range traversed and the direction of frequency modulation. One sound was defined as target and required a button press. The results of ERPs (N1, P2, N2, and P3) were consistent with previous studies. Analysis of evoked gamma-band responses yielded no significant task-dependent modulation, but we observed a stimulus dependency, which was also present in a control experiment: The amplitude of evoked gamma responses showed an inverted U-shape as a function of stimulus frequency. Investigation of total gamma activity revealed functionally relevant responses at high frequencies (90 Hz to 250 Hz), which showed significant modulations by matches with STM: Complete matches led to the strongest enhancements (starting around 100 ms after stimulus onset) and partial matches resulted in intermediate ones. The results support the conclusion that very high frequency oscillations (VHFOs) are markers of active stimulus discrimination in STM matching processes and are attributable to higher cognitive functions.

Fluoroaluminate stimulates phosphorylation of p130 Cas and Fak and increases attachment and spreading of preosteoblastic MC3T3-E1 cells

Fluoroaluminate is a G-protein activator, it stimulates osteoblastic cells in culture, and is a bone-forming agent in vivo. To elucidate the mechanisms of G-protein-mediated action of fluoroaluminate in osteoblasts, we studied protein tyrosine phosphorylation in the preosteoblastic cell line MC3T3-E1. Fluoroaluminate, lysophosphatidic acid (LPA; an agonist for G-protein-coupled receptor), or adhesion to type I collagen all stimulated phosphorylation of a similar set of proteins, including p130, p120, p110 (previously identified as proline-rich tyrosine kinase 2, Pyk2), and p70. The phosphorylation of these proteins was sensitive to an Src inhibitor, but not to a Gi-protein inactivator, pertussis toxin. By purification/mass spectrometry and by immunodepletion, p130 protein was identified as p130 Cas (Crk-associated protein), a Src substrate and a protein involved in signaling by cell-adhesion receptors, integrins. Phosphorylation of immunoprecipitated p130 Cas increased upon stimulation with fluoroaluminate and with agonists of G-protein-coupled receptors, but not with growth factors. By immunodepletion, the p120 protein was identified as focal adhesion kinase, Fak. The addition of fluoroaluminate during cell attachment to type I collagen further stimulated phosphorylation of p130 Cas and of Fak. Simultaneously, fluoroaluminate increased the number of attached MC3T3-E1 cells and their spreading. These novel aspects of fluoroaluminate action in cell culture may be important for the bone-forming action of fluoroaluminate in vivo.

[Angioendotheliomatosis proliferans systematizata]

Angioendotheliomatosis proliferans systematisata comprises two different entities; a malignant and benign (reactive) form. The more common malignant form with a fatal prognosis should be termed intravascular or angiotropic lymphoma and is a multifocal systemic disease, which affects especially the small and middle-sized blood vessels of the skin and central nervous system. Reactive angioendotheliomatosis is a benign disease, often associated with an infectious disease (predominantly with subacute bacterial endocarditis). We report a 38-year-old woman with a reactive angioendotheliomatosis and a 68-year-old man diagnosed as having the rare T-cell type of intravascular lymphoma.

Determination of the origin of charge heterogeneity in a murine monoclonal antibody

PURPOSE

The aim of this study was to elucidate the molecular basis of charge heterogeneity found in a purified monoclonal IgG1 antibody, MMA383.

METHODS

Cation exchange chromatography (CEX) and isoelectric focusing (IEF) were used to monitor charge heterogeneity. CEX in conjunction with carboxypeptidase B digests of the antibody was used to determine the contribution of C-terminal lysines to MMA383 charge heterogeneity. Potential chemical degradation sites were identified by peptide mapping of individual chains, with peptide identification by mass spectrometry (MALDI-TOF MS). Peptide sequencing was used to determine specific deamidation sites. Binding constants of predominant isoforms were compared by surface plasmon resonance (SPR).

RESULTS

Extensive charge heterogeneity of purified MMA383 was detected by CEX and IEF. Removal of C-terminal lysines simplified the IEF pattern to nine predominant isoforms. Quantitation of isoaspartate in each of the isoforms indicated deamidation of MMA383 as a major cause of charge heterogeneity. CEX of the individual isoform chains suggested the presence of one deamidation site on each of the heavy and light chains. The two sites of deamidation were identified using peptide mapping, sequencing and mass spectrometry. SPR results showed no significant difference in the binding parameters among the isoforms.

CONCLUSIONS

C-terminal lysine microheterogeneity and deamidation of Asn141 in the heavy chain and Asn161 in the light chain are the major causes of MMA383 charge heterogeneity. Identification of the two deamidation sites will allow replacement of these amino acids in order to create a product less susceptible to degradation.

Increased small bowel epithelial turnover in interleukin-1 receptor knockout mice

OBJECTIVE

To determine whether interleukin-1 (IL-1) affects the cellular homeostasis of small bowel mucosa, the authors studied apoptosis and proliferation in small bowel epithelium in two groups of C57 mice: an IL-1 receptor knockout group, and a control wild-type group.

SUMMARY BACKGROUND DATA

Gut mucosal integrity is maintained by a balance of cell proliferation and cell death. Recent reports suggest that IL-1, a proinflammatory cytokine, increases cell death by apoptosis in some epithelial cells.

METHODS

Twenty-four male C57BL6 IL-1 receptor (type I) knockout mice were killed, and small bowel was removed for study. Twenty-four wild-type mice (C57-BL6) served as controls. Body weights, bowel length, and mucosal morphology were examined for phenotypic differences. Apoptosis was quantified by terminal deoxyuridine nick-end labeling (TUNEL) immunohistochemical staining and cellular proliferation by proliferation cell nuclear antigen staining. Whole mucosal protein was analyzed for nuclear factor-kappaB expression. Groups were analyzed by t test.

RESULTS

The absence of IL-1 type I receptor in knockout mice was verified by reverse transcriptase-polymerase chain reaction. IL-1 receptor null mice were larger than wild-type controls, with a longer small bowel; however, the index of small bowel length to total body weight did not differ between groups. The percentage of apoptotic cells was higher in IL-1 receptor null mice than in wild-type mice; the proliferation index also increased. Mucosal height and other measures of mucosal morphology were not different. Genotypic absence of IL-1 receptors was associated with decreased expression of nuclear factor-kappaB in whole mucosal protein extracts.

CONCLUSIONS

Both apoptosis and proliferation increased in gut epithelial cells of mice without IL-1 receptors, suggesting increased cell turnover with no change in net balance. This model represents an opportunity to examine potential mechanisms of gut epithelial turnover in vivo, under both normal conditions and in conditions of mucosal proliferation and atrophy.

A novel inhibitor of the tyrosine kinase Src suppresses phosphorylation of its major cellular substrates and reduces bone resorption in vitro and in rodent models in vivo

The tyrosine kinase Src has been implicated in the process of osteoclast-mediated bone resorption. Here, we describe a novel class of Src inhibitors, substituted 5,7-diphenyl-pyrrolo[2,3-d]pyrimidines, and characterize one of them, CGP77675, in vitro and in models of bone resorption in vivo. In vitro, CGP77675 inhibited phosphorylation of peptide substrates and autophosphorylation of purified Src (concentration producing half-maximal inhibition [IC50] values 5-20 and 40 nmol/L, respectively). The compound was selective toward other protein kinases: the Src IC50 value was lower than those for Cdc2 (>500-fold), epidermal growth factor (EGF) receptor (7.5-fold), and vascular endothelial growth factor receptor (>50-fold), and for v-Abl (15-fold) and focal adhesion kinase (Fak) (>25-fold). The Src kinase family members Lck and Yes were inhibited with IC50 values 20-fold higher than or equal to Src. To measure the inhibition of cellular Src activity, we identified the major tyrosine-phosphorylated proteins in an Src-overexpressing cell line IC8.1 as Src, Fak, and paxillin. CGP77675 potently inhibited tyrosine phosphorylation of the Src substrates Fak and paxillin, but had much less effect on Src (IC50 values 0.3, 0.5, and 5.7 micromol/L). The phosphorylation of Src in IC8.1 cells reflected phosphorylation of the negative regulatory tyrosine 527 (Y527); thus, the inhibitor was selective against the Y527 C-terminal Src kinase Csk. In osteoblastic MC3T3-E1 cells, CGP77675 inhibited signaling induced by PDGF at the receptor level, but not signaling by EGF, basic fibroblast growth factor, insulin-like growth factor-1, and phorbol 12-myristate 13-acetate. The effect of CGP77675 on bone resorption was evaluated in vitro and in vivo. The parathyroid hormone-induced bone resorption in rat fetal long bone cultures was inhibited with an IC50 of 0.8 micromol/L. CGP77675 dose-dependently reduced the hypercalcemia induced in mice by interleukin-1beta and partly prevented bone loss and microarchitectural changes in young ovariectomized rats, showing that the protective effect on bone was exerted via the inhibition of bone resorption. Thus, specific Src family kinase inhibitors may be useful for the treatment of diseases associated with elevated bone loss.

Expression of Src family kinases and their putative substrates in the human preosteoclastic cell line FLG 29.1

Several lines of evidence suggest that the c-Src tyrosine kinase has a specific role in bone-resorbing osteoclasts. To investigate this further, we examined the expression of c-Src, its kinase family members, and their putative substrates in the human leukemia cell line FLG 29.1. Western blot analysis with specific antibodies against Src family members showed expression of Src, Fyn, and Lyn, lower levels of Yes and Hck, and the absence of Lck tyrosine kinase. During a 3-day treatment with phorbol 12-myristate, 13-acetate (PMA), which induces differentiation of FLG 29.1 cells toward an osteoclast-like phenotype, the levels of Src and Fyn increased and the levels of Lyn decreased. In a similar leukemia cell line, HL-60, Src protein was not constitutively expressed and not induced by PMA treatment, which leads to monocytic differentiation. PMA treatment of FLG 29.1 cells induced a strong increase in the expression of p120 Cbl and Pyk2 kinase, which are putative Src substrates. Pyk2 phosphorylation increased upon adherence of FLG 29.1 cells to fibronectin and to ST2 stromal cells. The expression of other Src substrates and interacting proteins, such as p120 Cas, p130 Cas, vinculin, Fak kinase, and the p85 phosphatidylinositol 3-kinase subunit either did not change or slightly increased during PMA treatment. The elevated total protein tyrosine phosphorylation in PMA-treated FLG 29.1 cells was abolished by herbimycin A, a Src inhibitor. These data are consistent with the proposed role of Src in the osteoclastic function and support the use of FLG 29.1 cells as a model to study Src substrates in the cells of the osteoclastic lineage.

Fluoroaluminate induces activation and association of Src and Pyk2 tyrosine kinases in osteoblastic MC3T3-E1 cells

Fluoride is known to increase bone mass in vivo, probably through stimulation of osteoblast proliferation; however, the mechanisms of fluoroaluminate action in osteoblasts have not yet been elucidated. We have previously shown that in osteoblastic MC3T3-E1 cells, fluoroaluminate stimulates G protein-mediated protein tyrosine phosphorylation (Scaronuscarona, M., Standke, G. J. R., Jeschke, M., and Rohner, D. (1997) Biochem. Biophys. Res. Commun. 235, 680-684). Although the Ser/Thr kinases Erk1, Erk2, and p70(S6K) were activated in response to fluoroaluminate, the identity of fluoroaluminate-activated tyrosine kinase(s) remained elusive. In this study, we show that in MC3T3-E1 cells, fluoroaluminate induces a 110-kDa tyrosine-phosphorylated protein that we identify as Pyk2, a cytoplasmic tyrosine kinase related to Fak (focal adhesion kinase). The tyrosine phosphorylation of Pyk2 increased in a dose- and time-dependent manner. The autophosphorylation activity of Pyk2 increased 3-fold and reached its maximum within 10 min of fluoroaluminate treatment. Fluoroaluminate also induced activation of Src and the association of Pyk2 with Src. The phosphorylation of Src-associated Pyk2 increased >20-fold in in vitro kinase assays, suggesting that Pyk2 is phosphorylated by Src. Although MC3T3-E1 cells express much more Fak than Pyk2, Src preferentially associated with Pyk2. In vitro, Pyk2 bound to the Src SH2 domain, suggesting that this interaction mediates the Src-Pyk2 association in cells. These data indicate that osteoblastic cells express Pyk2, which is tyrosine-phosphorylated and activated in response to G protein activation by fluoroaluminate, and that the mechanism of Pyk2 activation most likely involves Src. Thus, Src and Pyk2 are tyrosine kinases involved in G protein-mediated tyrosine phosphorylation in osteoblastic cells and may be important for the osteogenic action of fluoroaluminate.

Fluoroaluminate induces pertussis toxin-sensitive protein phosphorylation: differences in MC3T3-E1 osteoblastic and NIH3T3 fibroblastic cells

Fluoride is an acknowledged bone-forming agent that may act through stimulation of osteoblast proliferation. Fluoride's action on osteoblasts and bone is potentiated by aluminum, which can form a complex with fluoride (fluoroaluminate) and activate heterotrimeric G proteins. Here we examined signaling pathways activated by fluoroaluminate in MC3T3-E1 osteoblastic and in NIH3T3 fibroblastic cells. In MC3T3-E1 cells, fluoroaluminate induced a decrease in cAMP levels and an increase in MAP and p70 S6 kinase phosphorylations. These responses were partially or completely prevented by pertussis toxin, an inhibitor of G alpha i proteins. In NIH3T3 cells, fluoroaluminate induced weaker tyrosine and MAP kinase phosphorylations. Fluoroaluminate, but not PDGF, induced a long-lasting tyrosine phosphorylation of a 130 kDa protein only in MC3T3-E1 cells. The expression of G alpha i2, but not of G alpha s and G alpha q/11 proteins was about 10-fold higher in MC3T3-E1 cells. Thus, different signaling in osteoblastic and fibroblastic cells may be due to differential expression of G alpha i proteins and tyrosine kinase substrates and could underlie fluoride's pharmacological action in bone.

Intra-tumoral application of a heregulin-exotoxin-a fusion protein causes rapid tumor regression without adverse systemic or local effects

Tumor toxins are recombinant, bifunctional proteins which comprise a tumor-cell-specific recognition domain and an enzymatic toxin domain. We have evaluated the in vivo effects of a tumor toxin that specifically recognizes the erbB-3 and erbB-4 receptors (HRG beta 1-ETA). High doses of HRG beta 1-ETA administered systemically (intracardially or intraperitoneally) caused acute liver necrosis and were lethal. The same dose of tumor toxins applied subcutaneously had no detectable histopathological effects. The anti-tumor activity of HRG beta 1-ETA was tested in nude mice with xenografts of a human breast tumor, MAXF1162. The MAXF1162 tumor grew rapidly upon s.c. implantation. Intra-tumoral application of HRG beta 1-ETA (7 times 5 micrograms over a period of 21 days) induced complete regression of tumors. At the time the treatment was terminated, no tumor cells were detectable microscopically. Evaluation of the liver of treated animals revealed no significant toxicity in the effective dose range. These experiments indicate that tumor toxins can become valuable for local tumor treatment and for reduction of tumor burden.

Laminin activates the p185HER2 oncoprotein and mediates growth inhibition of breast carcinoma cells

The interaction between laminin and the oncoprotein encoded by the c-erbB-2 oncogene was studied in vitro and in vivo in human breast carcinomas. In vitro analysis of breast carcinoma cell lines overexpressing p185HER2 revealed that laminin, but not fibronectin, induced tyrosine phosphorylation and down-modulation of oncoprotein membrane expression. Laminin also specifically inhibited growth of p185HER2-positive cell lines. No direct binding between the recombinant extracellular domain of p185HER2 and laminin was found. Induction of oncoprotein down-modulation by anti-integrin antibodies and coprecipitation of the oncoprotein with the beta 4 integrin subunit indicate that the interaction between p185HER2 and laminin occurs through integrin molecules. The relevance of this in vitro observation was verified in vivo by analysing the prognostic value of p185HER2 overexpression as a function of laminin production on archival paraffin-embedded sections of 887 primary breast tumours. The results revealed an association between p185HER2 overexpression and unfavourable prognosis in tumours negative for laminin production, whereas in laminin-producing tumours, the oncoprotein overexpression was not associated with tumour aggressiveness.

Expression of chimeric envelope proteins in helper cell lines and integration into Moloney murine leukemia virus particles

New retroviral constructs with a grafted specificity of infection could become useful gene delivery vehicles with applications in systemic gene therapy. We have constructed retroviral vectors to target gene transfer to human tumor cells. Chimeric envelope proteins have been expressed to obtain viral particles with a defined specificity of infection. Two tumor cell-specific recognition domains were cloned and fused with the viral envelope gene. A recognition domain specific for ErbB-2 expressing tumor cells was derived from a monoclonal antibody directed against the ErbB-2 receptor in the form of a single chain antibody domain (scFv-erbB-2). The receptor binding domain was derived from the heregulin gene (HRG70). This domain provides recognition specificity for ErbB-3 and ErbB-4 receptor expressing tumor cells. The recognition domains were inserted at the amino terminal end into the MoMLV envelope gene. Helper cell lines were established which express the recombinant envelope protein genes, the gag and pol genes and packageable retroviral RNA. The analysis of the helper cell line revealed that the recombinant ErbB-2 scFv-envelope protein was expressed, but not incorporated into viral particles. The scFv-erbB-2 envelope protein was not inserted into the cell membrane and the assembly of retroviral particles was not completed. In contrast, the HRG70-envelope protein was expressed on the surface of the helper cells and incorporated into retroviral particles. The HRG70-envelope protein, however, did not alter the host range of infection. Only cells expressing the ecotropic viral receptor could be infected.

Biotechnological and gene therapeutic strategies in cancer treatment

New anti-cancer agents are being developed which incorporate cancer-cell-specific recognition functions and are thus able to distinguish between normal and tumor cells. Recognition is dependent on the enhanced expression of antigenic determinants on the surface of tumor cells. The ErbB-2 receptor (ErbB-2R) is overproduced in a high percentage of adenocarcinomas arising in the breast, ovary, lung and stomach, when compared to normal cells. The tumor-enriched expression and extracellular accessibility make this receptor a suitable target for directed tumor therapy. A gene expressing the single-chain antibody molecule (scFv), specific for the extracellular domain of the ErbB-2R, was constructed by joining cDNAs encoding the light- and heavy-chain variable domains of the monoclonal antibody (mAb) FRP5. This scFv-encoding gene has been used as a targeting domain for two effectors: (i) A recombinant immunotoxin-encoding gene was constructed by adding sequences encoding a modified Pseudomonas aeroginosa exotoxin A (ETA) to the scFv-encoding DNA. (ii) Cytotoxic T-lymphocytes (CTL) with specificity for ErbB-2R-producing tumor cells were generated by retroviral transfer of a chimeric gene which encodes the scFv(FRP5), a hinge region and the zeta-chain of the T-cell receptor (TCR) complex. The bacterially produced recombinant immunotoxin scFv(FRP5)-ETA binds specifically to the ErbB-2R and displays both in vitro and in vivo cytotoxic effects selective for tumor cells producing high levels of the ErbB-2R. Target cells expressing the ErbB-2R gene were lysed in vitro with high specificity by the scFv::hinge::zeta-expressing T-cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Targeted inhibition of tumor-cell growth by recombinant heregulin-toxin fusion proteins

Fusion of functional domains of proteins by in vitro recombination of gene fragments can be used to generate novel anti-tumor agents. The combination of tumor-cell-recognition functions and toxic functions results in cytotoxic molecules with a high specificity for tumor cells. Human adenocarcinomas are frequently characterized by over-expression of members of the epidermal-growth-factor (EGF) receptor family (ErbB-1, 2, 3 and 4), when compared with normal cells. These tumors are particularly suited to treatment with recombinant toxins. The human heregulins (HRG) and their rat counterparts (neu differentiation factor, NDF) have been identified as ligands for these receptors. Two chimeric heregulin-toxin fusions consisting of the EGF-like receptor recognition domain of the heregulin isoforms HRG alpha and HRG beta I, and the domains II, Ib and III of the Pseudomonas exotoxin A (ETA) were constructed. HRG beta I-ETA is highly cytotoxic for the mammary carcinoma cell lines SK-BR-3 and MDA-MB-453. HRG alpha-ETA was less active than HRG beta I-ETA. The killing activity of the recombinant toxins correlated with the expression levels of ErbB-3 and/or ErbB-4 in the cell lines studied. High expression of ErbB-2 is not sufficient to confer sensitivity towards the HRG-ETA. Treatment of mice with 0.4 mg/kg/day of HRG beta I-ETA caused growth retardation of transplanted human breast tumor cells. Higher levels of HRG beta I-ETA administration resulted in acute hemorrhagic necrosis of the liver.

NDF/heregulin activates MAP kinase and p70/p85 S6 kinase during proliferation or differentiation of mammary epithelial cells

Neu differentiation factors (NDF) are a novel family of polypeptide factors which activate sub-class I tyrosine kinase receptors. In all mammary epithelial cells analysed in this study, NDF activates the same signalling pathways while it induces different, cell-specific biological effects. In AU565 cells which are growth inhibited, as well as in T47D or HC11 cells which proliferate in response to NDF, the MAP kinase isoforms p44ERK1 and p42ERK2 and the p70/p85 S6 kinase are activated. NDF stimulates tyrosine phosphorylation and the in vitro kinase activity of ErbB-2. When PKC is activated by TPA, NDF is no longer able to activate ErbB-2 in T47D cells, leading to a blockage of cell proliferation. Activation of ErbB-2 by point mutation, or by monoclonal antibodies, also stimulates both the MAPK and the p70/p85 S6 kinase pathways. The same monoclonal antibodies can induce AU565 cell differentiation. In summary, during growth or differentiation of mammary epithelial cells, NDF stimulates several independent signalling pathways which can also be triggered by ErbB-2 stimulation alone. PKC activation blocks the biological effect induced by NDF through negative modulation of ErbB-2.

Neu differentiation factor/heregulin modulates growth and differentiation of HC11 mammary epithelial cells

The HC11 mouse mammary epithelial cell line has proven to be a valuable in vitro model to study the roles of peptide factors and hormones involved in the growth and differentiation of mammary cells. Treatment of HC11 cells with the lactogenic hormones, dexamethasone, insulin, and PRL (DIP), leads to cellular differentiation and production of the milk protein beta-casein. We have analyzed the effects of Neu differentiation factor (NDF)/heregulin, a newly described activating ligand for erbB-2 and other members of the epidermal growth factor (EGF) receptor family, on cell growth and the expression of milk proteins in HC11 cells. In these cells, NDF induces tyrosine phosphorylation of erbB-2 and erbB-3. Both NDF and EGF stimulate HC11 cell proliferation and promote the responsiveness of HC11 cells to lactogenic hormones. NDF induces the expression of a 22-kilodalton milk protein. This protein is up-regulated by other factors, including dexamethasone, EGF, and basic fibroblast growth factor, and is controlled in a manner distinct from that of beta-casein. Like EGF, NDF inhibits the DIP-induced expression of beta-casein at the level of transcription. The inhibition is due to the negative effect of NDF on the activation of mammary gland factor (MGF/Stat5), a member of the Stat family of transcription factors, which is essential for beta-casein gene expression.

Experimental improvement of microvascular allografts with the new material polyurethane and microvessel endothelial cell seeding

The major aim of this experimental study was the improvement of hemo- and biocompatibility of microvascular allografts. Comparison of polyurethane and ePTFE (expanded polytetrafluoroethene) micrografts did not show a significant advantage of the new material polyurethane. When the endothelial cell seeding method was applied, endothelial cell harvesting from rat fat proved to be very difficult. Therefore, further research on microvessel endothelial cell seeding is planned.

Existent T-cell and antibody immunity to HER-2/neu protein in patients with breast cancer

The HER-2/neu protooncogene is amplified and overexpressed in 20-40% of invasive breast cancers. HER-2/neu protein overexpression is associated with aggressive disease and is an independent predictor of poor prognosis in several subsets of patients. The protein may also be related to cancer formation, with overexpression being detectable in 50-60% of ductal carcinomas in situ. It has been suggested that it might be possible to develop specific T-cell therapy directed against proteins involved in malignant transformation. One question is whether normal proteins that are overexpressed are appropriate targets for therapeutic immune attack. This report demonstrates that some patients with HER-2/neu-positive breast cancers have both existent CD4+ helper/inducer T-cell immunity and antibody-mediated immunity to HER-2/neu protein. Initial studies performed on 20 premenopausal breast cancer patients identified antibodies to HER-2/neu in 11 individuals. Similar antibody responses have been found in some normal individuals. The patient with the greatest antibody response was studied in detail. In addition to a humoral immune response this patient had evidence of a significant proliferative T-cell response to the HER-2/neu protein and peptides. Similar T-cell responses have been detected in additional patients. It has been assumed that patients would be immunologically tolerant to HER-2/neu as a self-protein and that immunity might be difficult to generate. If immunity could be generated, the result might be destructive autoimmunity. The current data support the notion that HER-2/neu-specific immunity might be used in therapy without destroying normal tissue but also raises questions as to the role of existent immunity in immune surveillance and cancer progression.