Differential Effects of Astrocyte Manipulations on Learned Motor Behavior and Neuronal Ensembles in the Motor Cortex

Although motor cortex is crucial for learning precise and reliable movements, whether and how astrocytes contribute to its plasticity and function during motor learning is unknown. Here, we report that astrocyte-specific manipulations in primary motor cortex (M1) during a lever push task alter motor learning and execution, as well as the underlying neuronal population coding. Mice that express decreased levels of the astrocyte glutamate transporter 1 (GLT1) show impaired and variable movement trajectories, whereas mice with increased astrocyte Gq signaling show decreased performance rates, delayed response times, and impaired trajectories. In both groups, which include male and female mice, M1 neurons have altered interneuronal correlations and impaired population representations of task parameters, including response time and movement trajectories. RNA sequencing further supports a role for M1 astrocytes in motor learning and shows changes in astrocytic expression of glutamate transporter genes, GABA transporter genes, and extracellular matrix protein genes in mice that have acquired this learned behavior. Thus, astrocytes coordinate M1 neuronal activity during motor learning, and our results suggest that this contributes to learned movement execution and dexterity through mechanisms that include regulation of neurotransmitter transport and calcium signaling.SIGNIFICANCE STATEMENT We demonstrate for the first time that in the M1 of mice, astrocyte function is critical for coordinating neuronal population activity during motor learning. We demonstrate that knockdown of astrocyte glutamate transporter GLT1 affects specific components of learning, such as smooth trajectory formation. Altering astrocyte calcium signaling by activation of Gq-DREADD upregulates GLT1 and affects other components of learning, such as response rates and reaction times as well as trajectory smoothness. In both manipulations, neuronal activity in motor cortex is dysregulated, but in different ways. Thus, astrocytes have a crucial role in motor learning via their influence on motor cortex neurons, and they do so by mechanisms that include regulation of glutamate transport and calcium signals.

Label-free three-photon imaging of intact human cerebral organoids for tracking early events in brain development and deficits in Rett syndrome

Human cerebral organoids are unique in their development of progenitor-rich zones akin to ventricular zones from which neuronal progenitors differentiate and migrate radially. Analyses of cerebral organoids thus far have been performed in sectioned tissue or in superficial layers due to their high scattering properties. Here, we demonstrate label-free three-photon imaging of whole, uncleared intact organoids (~2 mm depth) to assess early events of early human brain development. Optimizing a custom-made three-photon microscope to image intact cerebral organoids generated from Rett Syndrome patients, we show defects in the ventricular zone volumetric structure of mutant organoids compared to isogenic control organoids. Long-term imaging live organoids reveals that shorter migration distances and slower migration speeds of mutant radially migrating neurons are associated with more tortuous trajectories. Our label-free imaging system constitutes a particularly useful platform for tracking normal and abnormal development in individual organoids, as well as for screening therapeutic molecules via intact organoid imaging.

POS1186 STUDY OF SPONDYLODISCITIS WITHOUT BACTERIOLOGICAL DOCUMENTATION FROM A COHORT OF 142 PATIENTS WITH SUSPECTED INFECTIOUS SPONDYLODISCITIS ON IMAGING

Background

The incidence of infectious spondylodiscitis was estimated at 2.4/100,000 people in 2002. When faced with an image of spondylodiscitis on imaging, infectious spondylodiscitis is the most feared etiology. In recent years, several non-infectious spondylodiscitis etiologies have been described: Andersson lesion, crystal-induced discopathy, degenerative changes, etc (2). The identification of the germ by blood cultures or disc-vertebral puncture-biopsy allows the treatment to be best adapted antibiotic. Bacteriological investigation is inconclusive in about 30% (1). More and more undocumented spondylodiscitis are described.

Objectives

The aim of this study is to describe a cohort of spondylodiscitis without bacteriological documentation and to compare it to spondylodiscitis with bacteriological documentation.

Methods

Using a “clinical data warehouse”, we searched for the key word “spondylodiscitis” in the documents associated with hospitalisations in the Rheumatology department of the Rouen University Hospital between 2010 and 2020. Four hundred and twenty-two records were analysed: 196 were excluded because they were not hospitalizedn in Rheumatology, among the 226 suspected spondylodiscitis, imaging allowed us to exclude 84 records for which there was no infectious spondylodiscitis and to retain 142 records. We collected demographic data, history, clinical symptoms, results of imaging, biological and bacteriological examinations. Statistical analysis was performed by Fisher’s exact test for qualitative data and by Mann-Whitney test for quantitative data.

Results

Four hundred and twenty-two patients were collected, 142 were analyzed. The average age was 65.5 +/- 14 years, 64.1% were male. Spinal pain was present in 96.5% of the cases without any difference between the two groups. One hundred and nine cases of spondylodiscitis were documented, of which 72 were confirmed by blood cultures and 36 by spinal disc biopsy. Thirty-three were not documented. Documented spondylodiscitis was more often febrile (41.3% vs 15.21% in undocumented cases, p = 0.006), had a greater biological inflammatory syndrome (mean CRP 152.4 +/- 112.6 mg/L versus 73 +/- 73.1 mg/L, p < 0.0001), and had been evolving for a shorter period of time than undocumented spondylodiscitis (54.1% vs 24.2% less than one month). Staphylococcus aureus was the most frequently retrieved bacteria 27.5%, followed by coagulase-negative staphylococci and streptococci (18.3% and 19.3% respectively). One hundred and twenty-one patients (85%) had an MRI at diagnosis; one hundred and two (71.8%) had a CT scan; and 81 patients (57%) had both examinations. The imaging analysis showed that there was no difference in soft tissue infiltration, erosions and abscesses. Probabilistic antibiotic therapy was proposed in 28/33 (84.5%) of cases. After collegial discussion, the alternative diagnoses retained were degenerative disc disease (4 cases), spinal gout (1 case), spondyloarthritis (1 case).

Conclusion

Undocumented spondylodiscitis is a recurrent problem in hospital practice. Alternative diagnoses are increasingly reported, their diagnosis is based on a collegial discussion.

References

[1]Avenel G et Al. Eur J Clin Microbiol Infect Dis. 2021.

[2]Morales H. Semin Ultrasound CT MR. 2018.

Disclosure of Interests

None declared

Molecular Signatures of Response to Mecasermin in Children With Rett Syndrome

Rett syndrome (RTT) is a devastating neurodevelopmental disorder without effective treatments. Attempts at developing targetted therapies have been relatively unsuccessful, at least in part, because the genotypical and phenotypical variability of the disorder. Therefore, identification of biomarkers of response and patients' stratification are high priorities. Administration of Insulin-like Growth Factor 1 (IGF-1) and related compounds leads to significant reversal of RTT-like symptoms in preclinical mouse models. However, improvements in corresponding clinical trials have not been consistent. A 20-weeks phase I open label trial of mecasermin (recombinant human IGF-1) in children with RTT demonstrated significant improvements in breathing phenotypes. However, a subsequent randomised controlled phase II trial did not show significant improvements in primary outcomes although two secondary clinical endpoints showed positive changes. To identify molecular biomarkers of response and surrogate endpoints, we used RNA sequencing to measure differential gene expression in whole blood samples of participants in the abovementioned phase I mecasermin trial. When all participants (n = 9) were analysed, gene expression was unchanged during the study (baseline vs. end of treatment, T0-T3). However, when participants were subclassified in terms of breathing phenotype improvement, specifically by their plethysmography-based apnoea index, individuals with moderate-severe apnoea and breathing improvement (Responder group) displayed significantly different transcript profiles compared to the other participants in the study (Mecasermin Study Reference group, MSR). Many of the differentially expressed genes are involved in the regulation of cell cycle processes and immune responses, as well as in IGF-1 signalling and breathing regulation. While the Responder group showed limited gene expression changes in response to mecasermin, the MSR group displayed marked differences in the expression of genes associated with inflammatory processes (e.g., neutrophil activation, complement activation) throughout the trial. Our analyses revealed gene expression profiles associated with severe breathing phenotype and its improvement after mecasermin administration in RTT, and suggest that inflammatory/immune pathways and IGF-1 signalling contribute to treatment response. Overall, these data support the notion that transcript profiles have potential as biomarkers of response to IGF-1 and related compounds.

A low-cost 3D printed microfluidic bioreactor and imaging chamber for live-organoid imaging

Organoids are biological systems grown in vitro and are observed to self-organize into 3D cellular tissues of specific organs. Brain organoids have emerged as valuable models for the study of human brain development in health and disease. Researchers are now in need of improved culturing and imaging tools to capture the in vitro dynamics of development processes in the brain. Here, we describe the design of a microfluidic chip and bioreactor, to enable in situ tracking and imaging of brain organoids on-chip. The low-cost 3D printed microfluidic bioreactor supports organoid growth and provides an optimal imaging chamber for live-organoid imaging, with drug delivery support. This fully isolated design of a live-cell imaging and culturing platform enables long-term live-imaging of the intact live brain organoids as it grows. We can thus analyze their self-organization in a controlled environment with high temporal and spatial resolution.