A promising new treatment approach for major depressive disorder (MDD) targets the microbiota-gut-brain (MGB) axis, which is linked to physiological and behavioral functions affected in MDD. This is ...the first randomized controlled trial to determine whether short-term, high-dose probiotic supplementation reduces depressive symptoms along with gut microbial and neural changes in depressed patients. Patients with current depressive episodes took either a multi-strain probiotic supplement or placebo over 31 days additionally to treatment-as-usual. Assessments took place before, immediately after and again four weeks after the intervention. The Hamilton Depression Rating Sale (HAM-D) was assessed as primary outcome. Quantitative microbiome profiling and neuroimaging was used to detect changes along the MGB axis. In the sample that completed the intervention (probiotics N = 21, placebo N = 26), HAM-D scores decreased over time and interactions between time and group indicated a stronger decrease in the probiotics relative to the placebo group. Probiotics maintained microbial diversity and increased the abundance of the genus Lactobacillus, indicating the effectivity of the probiotics to increase specific taxa. The increase of the Lactobacillus was associated with decreased depressive symptoms in the probiotics group. Finally, putamen activation in response to neutral faces was significantly decreased after the probiotic intervention. Our data imply that an add-on probiotic treatment ameliorates depressive symptoms (HAM-D) along with changes in the gut microbiota and brain, which highlights the role of the MGB axis in MDD and emphasizes the potential of microbiota-related treatment approaches as accessible, pragmatic, and non-stigmatizing therapies in MDD. Trial Registration: www.clinicaltrials.gov , identifier: NCT02957591.
The multi‐C2 domain protein otoferlin is required for hearing and mutated in human deafness. Some OTOF mutations cause a mild elevation of auditory thresholds but strong impairment of speech ...perception. At elevated body temperature, hearing is lost. Mice homozygous for one of these mutations, OtofI515T/I515T, exhibit a moderate hearing impairment involving enhanced adaptation to continuous or repetitive sound stimulation. In OtofI515T/I515T inner hair cells (IHCs), otoferlin levels are diminished by 65%, and synaptic vesicles are enlarged. Exocytosis during prolonged stimulation is strongly reduced. This indicates that otoferlin is critical for the reformation of properly sized and fusion‐competent synaptic vesicles. Moreover, we found sustained exocytosis and sound encoding to scale with the amount of otoferlin at the plasma membrane. We identified a 20 amino acid motif including an RXR motif, presumably present in human but not in mouse otoferlin, which reduces the plasma membrane abundance of Ile515Thr‐otoferlin. Together, this likely explains the auditory synaptopathy at normal temperature and the temperature‐sensitive deafness in humans carrying the Ile515Thr mutation.
Synopsis
The Ile515Thr and the pachanga (Pga) mutations in otoferlin reduce the levels of otoferlin in auditory inner hair cells. Only the Pga mutation disturbs the plasma membrane abundance of otoferlin, which scales with spike rates in spiral ganglion neurons.
Otoferlin is critical for synaptic vesicle reformation from bulk‐endocytosed membrane.
Sustained IHC exocytosis and sound encoding depend on the amount of otoferlin at the plasma membrane, which can be reduced by mutations and/or elevated temperature.
Increased adaptation at IHC synapses and delayed recovery explain auditory fatigue due to otoferlin mutations.
An RXR motif presumably present in human but absent from mouse cochlear otoferlin further reduces the plasma membrane‐bound fraction of Ile515Thr‐otoferlin, thereby providing a molecular mechanism for the fever‐induced deafness in humans.
A mouse model of the human otoferlin Ile515Thr mutation provides insight into auditory synaptopathy at normal temperature and temperature‐sensitive deafness in humans carrying this mutation.
Depression is a debilitating disorder, and at least one third of patients do not respond to therapy. Associations between gut microbiota and depression have been observed in recent years, opening ...novel treatment avenues. Here, we present the first two patients with major depressive disorder ever treated with fecal microbiota transplantation as add-on therapy. Both improved their depressive symptoms 4 weeks after the transplantation. Effects lasted up to 8 weeks in one patient. Gastrointestinal symptoms, constipation in particular, were reflected in microbiome changes and improved in one patient. This report suggests further FMT studies in depression could be worth pursuing and adds to awareness as well as safety assurance, both crucial in determining the potential of FMT in depression treatment.
The transmembrane recognition complex (TRC40) pathway mediates the insertion of tail‐anchored (TA) proteins into membranes. Here, we demonstrate that otoferlin, a TA protein essential for hair cell ...exocytosis, is inserted into the endoplasmic reticulum (ER) via the TRC40 pathway. We mutated the TRC40 receptor tryptophan‐rich basic protein (Wrb) in hair cells of zebrafish and mice and studied the impact of defective TA protein insertion. Wrb disruption reduced otoferlin levels in hair cells and impaired hearing, which could be restored in zebrafish by transgenic Wrb rescue and otoferlin overexpression. Wrb‐deficient mouse inner hair cells (IHCs) displayed normal numbers of afferent synapses, Ca2+ channels, and membrane‐proximal vesicles, but contained fewer ribbon‐associated vesicles. Patch‐clamp of IHCs revealed impaired synaptic vesicle replenishment. In vivo recordings from postsynaptic spiral ganglion neurons showed a use‐dependent reduction in sound‐evoked spiking, corroborating the notion of impaired IHC vesicle replenishment. A human mutation affecting the transmembrane domain of otoferlin impaired its ER targeting and caused an auditory synaptopathy. We conclude that the TRC40 pathway is critical for hearing and propose that otoferlin is an essential substrate of this pathway in hair cells.
Synopsis
Otoferlin, a tail‐anchored protein of sensory hair cells, uses the transmembrane recognition complex (TRC40) pathway for ER membrane insertion. Disruption of the TRC40 receptor Wrb in hair cells impaired vesicle replenishment and hearing, most likely by reducing otoferlin levels.
Hearing requires membrane insertion of tail‐anchored (TA) proteins by the TRC40 pathway in hair cells.
The TA protein otoferlin, essential for hair cell exocytosis and defective in human deafness, utilizes the TRC40 pathway.
Deletion of TRC40 receptor WRB reduces otoferlin levels and impairs synaptic structure and function.
Reduced vesicle replenishment in WRB‐deficient hair cells impairs sound encoding.
ER membrane insertion of the sensory hair cell component otoferlin depends on the tail‐anchored protein insertion TRC40 pathway, whose disruption impairs synaptic vesicle replenishment and hearing.
Ca²⁺ influx triggers the fusion of synaptic vesicles at the presynaptic active zone (AZ). Here we demonstrate a role of Ras-related in brain 3 (Rab3)–interacting molecules 2α and β (RIM2α and RIM2β) ...in clustering voltage-gated CaV1.3 Ca²⁺ channels at the AZs of sensory inner hair cells (IHCs). We show that IHCs of hearing mice express mainly RIM2α, but also RIM2β and RIM3γ, which all localize to the AZs, as shown by immunofluorescence microscopy. Immunohistochemistry, patch-clamp, fluctuation analysis, and confocal Ca²⁺ imaging demonstrate that AZs of RIM2α-deficient IHCs cluster fewer synaptic CaV1.3 Ca²⁺ channels, resulting in reduced synaptic Ca²⁺ influx. Using superresolution microscopy, we found that Ca²⁺ channels remained clustered in stripes underneath anchored ribbons. Electron tomography of high-pressure frozen synapses revealed a reduced fraction of membrane-tethered vesicles, whereas the total number of membrane-proximal vesicles was unaltered. Membrane capacitance measurements revealed a reduction of exocytosis largely in proportion with the Ca²⁺ current, whereas the apparent Ca²⁺ dependence of exocytosis was unchanged. Hair cell-specific deletion of all RIM2 isoforms caused a stronger reduction of Ca²⁺ influx and exocytosis and significantly impaired the encoding of sound onset in the postsynaptic spiral ganglion neurons. Auditory brainstem responses indicated a mild hearing impairment on hair cell-specific deletion of all RIM2 isoforms or global inactivation of RIM2α. We conclude that RIM2α and RIM2β promote a large complement of synaptic Ca²⁺ channels at IHC AZs and are required for normal hearing.
Probiotics are suggested to improve depressive symptoms via the microbiota-gut-brain axis. We have recently shown a beneficial clinical effect of probiotic supplementation in patients with ...depression. Their underlying neural mechanisms remain unknown.
A multimodal neuroimaging approach including diffusion tensor imaging, resting-state functional MRI, and arterial spin labeling was used to investigate the effects of a four-weeks probiotic supplementation on fronto-limbic brain structure, function, and perfusion and whether these effects were related to symptom changes.
Thirty-two patients completed both imaging assessments (18 placebo and 14 probiotics group). Probiotics maintained mean diffusivity in the left uncinate fasciculus, stabilized it in the right uncinate fasciculus, and altered resting-state functional connectivity (rsFC) between limbic structures and the temporal pole to a cluster in the precuneus. Moreover, a cluster in the left superior parietal lobule showed altered rsFC to the subcallosal cortex, the left orbitofrontal cortex, and limbic structures after probiotics. In the probiotics group, structural and functional changes were partly related to decreases in depressive symptoms.
This study has a rather small sample size. An additional follow-up MRI session would be interesting for seeing clearer changes in the relevant brain regions as clinical effects were strongest in the follow-up.
Probiotic supplementation is suggested to prevent neuronal degeneration along the uncinate fasciculus and alter fronto-limbic rsFC, effects that are partly related to the improvement of depressive symptoms. Elucidating the neural mechanisms underlying probiotics' clinical effects on depression provide potential targets for the development of more precise probiotic treatments.
•Probiotic add-on intervention improved depressive symptoms in patients.•However, underlying neural mechanisms still remain unknown.•Probiotics impact fronto-limbic structure and function.•These brain changes are partly associated with clinical improvements.
In major depressive disorder (MDD), cognitive dysfunctions strongly contribute to functional impairments but are barely addressed in current therapies. Novel treatment strategies addressing cognitive ...symptoms in depression are needed. As the gut microbiota-brain axis is linked to depression and cognition, we investigated the effect of a 4-week high-dose probiotic supplementation on cognitive symptoms in depression.
This randomized controlled trial included 60 patients with MDD, of whom 43 entered modified intention-to-treat analysis. A probiotic supplement or indistinguishable placebo containing maltose was administered over 31 days in addition to treatment as usual for depression. Participant scores on the Verbal Learning Memory Test (VLMT), Corsi Block Tapping Test, and both Trail Making Test versions as well as brain-derived neurotrophic factor levels were assessed at 3 different time points: before, immediately after and 4 weeks after intervention. Additionally, brain activation changes during working memory processing were investigated before and immediately after intervention.
We found a significantly improved immediate recall in the VLMT in the probiotic group immediately after intervention, and a trend for a time × group interaction considering all time points. Furthermore, we found a time × group interaction in hippocampus activation during working memory processing, revealing a remediated hippocampus function in the probiotic group. Other measures did not reveal significant changes.
The modest sample size resulting from our exclusion of low-compliant cases should be considered.
Additional probiotic supplementation enhances verbal episodic memory and affects neural mechanisms underlying impaired cognition in MDD. The present findings support the importance of the gut microbiota-brain axis in MDD and emphasize the potential of microbiota-related regimens to treat cognitive symptoms in depression.
clinicaltrials.gov identifier NCT02957591.
Ca2+ influx triggers the fusion of synaptic vesicles at the presynaptic active zone (AZ). Here we demonstrate a role of Ras-related in brain 3 (Rab3)-interacting molecules 2a and β (RIM2a and RIM2β) ...in clustering voltage-gated CaV1.3 Ca2+ channels at the AZs of sensory inner hair cells (IHCs). We show that IHCs of hearing mice express mainly RIM2a, but also RIM2β and RIM3γ, which all localize to the AZs, as shown by immunofluorescence microscopy. Immunohistochemistry, patch-clamp, fluctuation analysis, and confocal Ca2+ imaging demonstrate that AZs of RIM2a-deficient IHCs cluster fewer synaptic CaV1.3 Ca2+ channels, resulting in reduced synaptic Ca2+ influx. Using superresolution microscopy, we found that Ca2+ channels remained clustered in stripes underneath anchored ribbons. Electron tomography of high-pressure frozen synapses revealed a reduced fraction of membrane-tethered vesicles, whereas the total number of membrane-proximal vesicles was unaltered. Membrane capacitance measurements revealed a reduction of exocytosis largely in proportion with the Ca2+ current, whereas the apparent Ca2+ dependence of exocytosis was unchanged. Hair cell-specific deletion of all RIM2 isoforms caused a stronger reduction of Ca2+ influx and exocytosis and significantly impaired the encoding of sound onset in the postsynaptic spiral ganglion neurons. Auditory brainstem responses indicated a mild hearing impairment on hair cell-specific deletion of all RIM2 isoforms or global inactivation of RIM2α. We conclude that RIM2α and RIM2β promote a large complement of synaptic Ca2+ channels at IHC AZs and are required for normal hearing.
Significance
Sound encoding relies on Ca
2+
-regulated transmitter release from inner hair cells (IHCs). Here we demonstrate a role of Ras-related in brain 3 (Rab3)–interacting molecule 2 (RIM2) in ...Ca
2+
channel-clustering and vesicle-tethering at the active zones of IHCs. Active zones of RIM2α-deficient IHCs cluster fewer synaptic voltage-gated Ca
V
1.3 Ca
2+
channels, resulting in reduced synaptic Ca
2+
influx. Exocytosis was diminished in RIM2α-deficient IHCs, likely contributing to the mild hearing impairment of RIM2α knockout mice. Hair cell-specific disruption of all RIM2 isoforms caused a stronger decrease of Ca
2+
current and exocytosis in IHCs and impaired the encoding of sound onset in spiral ganglion neurons. We conclude that RIM2α and RIM2β promote synaptic clustering of Ca
2+
channels at IHC active zones and are required for normal hearing.
Ca
2+
influx triggers the fusion of synaptic vesicles at the presynaptic active zone (AZ). Here we demonstrate a role of Ras-related in brain 3 (Rab3)–interacting molecules 2α and β (RIM2α and RIM2β) in clustering voltage-gated Ca
V
1.3 Ca
2+
channels at the AZs of sensory inner hair cells (IHCs). We show that IHCs of hearing mice express mainly RIM2α, but also RIM2β and RIM3γ, which all localize to the AZs, as shown by immunofluorescence microscopy. Immunohistochemistry, patch-clamp, fluctuation analysis, and confocal Ca
2+
imaging demonstrate that AZs of RIM2α-deficient IHCs cluster fewer synaptic Ca
V
1.3 Ca
2+
channels, resulting in reduced synaptic Ca
2+
influx. Using superresolution microscopy, we found that Ca
2+
channels remained clustered in stripes underneath anchored ribbons. Electron tomography of high-pressure frozen synapses revealed a reduced fraction of membrane-tethered vesicles, whereas the total number of membrane-proximal vesicles was unaltered. Membrane capacitance measurements revealed a reduction of exocytosis largely in proportion with the Ca
2+
current, whereas the apparent Ca
2+
dependence of exocytosis was unchanged. Hair cell-specific deletion of all RIM2 isoforms caused a stronger reduction of Ca
2+
influx and exocytosis and significantly impaired the encoding of sound onset in the postsynaptic spiral ganglion neurons. Auditory brainstem responses indicated a mild hearing impairment on hair cell-specific deletion of all RIM2 isoforms or global inactivation of RIM2α. We conclude that RIM2α and RIM2β promote a large complement of synaptic Ca
2+
channels at IHC AZs and are required for normal hearing.
Ca2+ influx triggers the fusion of synaptic vesicles at the presynaptic active zone (AZ). Here we demonstrate a role of Ras-related in brain 3 (Rab3)-interacting molecules 2a and beta (RIM2a and RIM2 ...beta ) in clustering voltage-gated CaV1.3 Ca2+ channels at the AZs of sensory inner hair cells (IHCs). We show that IHCs of hearing mice express mainly RIM2a, but also RIM2 beta and RIM3 gamma , which all localize to the AZs, as shown by immunofluorescence microscopy. Immunohistochemistry, patch-clamp, fluctuation analysis, and confocal Ca2+ imaging demonstrate that AZs of RIM2a-deficient IHCs cluster fewer synaptic CaV1.3 Ca2+ channels, resulting in reduced synaptic Ca2+ influx. Using superresolution microscopy, we found that Ca2+ channels remained clustered in stripes underneath anchored ribbons. Electron tomography of high-pressure frozen synapses revealed a reduced fraction of membrane-tethered vesicles, whereas the total number of membrane-proximal vesicles was unaltered. Membrane capacitance measurements revealed a reduction of exocytosis largely in proportion with the Ca2+ current, whereas the apparent Ca2+ dependence of exocytosis was unchanged. Hair cell-specific deletion of all RIM2 isoforms caused a stronger reduction of Ca2+ influx and exocytosis and significantly impaired the encoding of sound onset in the postsynaptic spiral ganglion neurons. Auditory brainstem responses indicated a mild hearing impairment on hair cell-specific deletion of all RIM2 isoforms or global inactivation of RIM2 alpha . We conclude that RIM2 alpha and RIM2 beta promote a large complement of synaptic Ca2+ channels at IHC AZs and are required for normal hearing.
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