A developmental stage- and Kidins220-dependent switch in astrocyte responsiveness to brain-derived neurotrophic factor

Refining the phenotype of SINO syndrome: A comprehensive cohort report of 14 novel cases

PURPOSE

Spastic paraplegia, intellectual disability, nystagmus, and obesity syndrome (SINO) is a rare autosomal dominant condition caused by heterozygous variants in KIDINS220. A total of 12 individuals are reported, comprising 8 with SINO and 4 with an autosomal recessive condition attributed to biallelic KIDINS220 variants.

METHODS

In our international cohort, we have included 14 individuals, carrying 13 novel pathogenic KIDINS220 variants in heterozygous form. We assessed the clinical and molecular data of our cohort and previously reported individuals and, based on functional experiments, reached a better understanding of the pathogenesis behind the KIDINS220-related disease.

RESULTS

Using fetal tissue and in vitro assays, we demonstrate that the variants generate KIDINS220 truncated forms that mislocalize in punctate intracellular structures, with decreased levels of the full-length protein, suggesting a trans-dominant negative effect. A total of 92% had their diagnosis within 3 years, with symptoms of developmental delay, spasticity, hypotonia, lack of eye contact, and nystagmus. We identified a KIDINS220 variant associated with fetal hydrocephalus and show that 58% of examined individuals present brain ventricular dilatation. We extend the phenotypic spectrum of SINO syndrome to behavioral manifestations not previously highlighted.

CONCLUSION

Our study provides further insights into the clinical spectrum, etiology, and predicted functional impact of KIDINS220 variants.

Kidins220 and Aiolos promote thymic iNKT cell development by reducing TCR signals

Development of T cells is controlled by the signal strength of the TCR. The scaffold protein kinase D-interacting substrate of 220 kilodalton (Kidins220) binds to the TCR; however, its role in T cell development was unknown. Here, we show that T cell-specific Kidins220 knockout (T-KO) mice have strongly reduced invariant natural killer T (iNKT) cell numbers and modest decreases in conventional T cells. Enhanced apoptosis due to increased TCR signaling in T-KO iNKT thymocytes of developmental stages 2 and 3 shows that Kidins220 down-regulates TCR signaling at these stages. scRNA-seq  indicated that the transcription factor Aiolos is down-regulated in Kidins220-deficient iNKT cells. Analysis of an Aiolos KO demonstrated that Aiolos is a downstream effector of Kidins220 during iNKT cell development. In the periphery, T-KO iNKT cells show reduced TCR signaling upon stimulation with α-galactosylceramide, suggesting that Kidins220 promotes TCR signaling in peripheral iNKT cells. Thus, Kidins220 reduces or promotes signaling dependent on the iNKT cell developmental stage.

Kidins220 regulates the development of B cells bearing the λ light chain

The ratio between κ and λ light chain (LC)-expressing B cells varies considerably between species. We recently identified Kinase D-interacting substrate of 220 kDa (Kidins220) as an interaction partner of the BCR. In vivo ablation of Kidins220 in B cells resulted in a marked reduction of λLC-expressing B cells. Kidins220 knockout B cells fail to open and recombine the genes of the Igl locus, even in genetic scenarios where the Igk genes cannot be rearranged or where the κLC confers autoreactivity. Igk gene recombination and expression in Kidins220-deficient B cells is normal. Kidins220 regulates the development of λLC B cells by enhancing the survival of developing B cells and thereby extending the time-window in which the Igl locus opens and the genes are rearranged and transcribed. Further, our data suggest that Kidins220 guarantees optimal pre-BCR and BCR signaling to induce Igl locus opening and gene recombination during B cell development and receptor editing.

Astrocytes and brain-derived neurotrophic factor (BDNF)

Astrocytes are emerging in the neuroscience field as crucial modulators of brain functions, from the molecular control of synaptic plasticity to orchestrating brain-wide circuit activity for cognitive processes. The cellular pathways through which astrocytes modulate neuronal activity and plasticity are quite diverse. In this review, we focus on neurotrophic pathways, mostly those mediated by brain-derived neurotrophic factor (BDNF). Neurotrophins are a well-known family of trophic factors with pleiotropic functions in neuronal survival, maturation and activity. Within the brain, BDNF is the most abundantly expressed and most studied of all neurotrophins. While we have detailed knowledge of the effect of BDNF on neurons, much less is known about its physiology on astroglia. However, over the last years new findings emerged demonstrating that astrocytes take an active part into BDNF physiology. In this work, we discuss the state-of-the-art knowledge about astrocytes and BDNF. Indeed, astrocytes sense extracellular BDNF through its specific TrkB receptors and activate intracellular responses that greatly vary depending on the brain area, stage of development and receptors expressed. Astrocytes also uptake and recycle BDNF / proBDNF at synapses contributing to synaptic plasticity. Finally, experimental evidence is now available describing deficits in astrocytic BDNF in several neuropathologies, suggesting that astrocytic BDNF may represent a promising target for clinical translation.

Retrospective study on the correlation between serum MIF level and the condition and prognosis of patients with traumatic head injury

Objective

This study aimed to investigate the correlation between serum levels of macrophage migration inhibitory factor (MIF) and the condition and prognosis of patients with traumatic brain injury (TBI).

Methods

A retrospective study design was used, and the clinical data of 131 TBI patients from February 2019 to January 2022 were analyzed. Patients were divided into mild (13-15 points), moderate (9-12 points), or severe (3-8 points) groups according to their Glasgow Coma Scale (GCS) score after admission. The serum levels of BDNF, MIF, and MBP in the three groups were compared, and their correlation with the severity of TBI was analyzed. Patients were then separated into a good prognosis group (4-5 points) and a poor prognosis group (≤3 points) based on their Glasgow Prognostic Score (GOS) after 6 months of follow-up. The predictive power of serum indexes and combined detection on prognosis was analyzed.

Results

Patients were classified into a mild group (n = 63), moderate group (n = 47), and severe group (n = 21) based on their GCS, with a significant difference noted in serum levels of MIF, MBP, and BDNF among patients with different degrees of severity (all P < 0.001). The MIF, MBP, and BDNF levels were lower in the mild group compared to the moderate (all P < 0.001) and severe group (all P < 0.001). Additionally, the MIF and BDNF levels in the moderate group were lower compared to the severe group (P = 0.011, P = 0.002). Patients with mild severity had lower serum MIF, MBP, and BDNF levels than those with other degrees, and these indexes were positively correlated with the severity of TBI (all P < 0.001, r = 0.62, r = 0.48, r = 0.58). Based on the GOS, patients were divided into a good prognosis group (n = 107) and a poor prognosis group (n = 24), with the levels of MIF, MBP, and BDNF in the good prognosis group being significantly lower than those in the poor prognosis group (P < 0.001, P = 0.007, P = 0.003). The area under the curve (AUC) of MIF was higher than that of MBP and BDNF in predicting the prognosis of TBI patients; however, the statistical differences were not significant (MIF vs. MBP, P = 0.239; MIF vs. BDNF, P = 0.211; BDNF vs. MBP, P = 0.899). The center line has a large displacement, CT annular cisterna compression, increased white blood cell count, MBP and BDNF were risk factors for prognosis in TBI patients (P = 0.005, P = 0.001, P = 0.005, P = 0.033, P = 0.044).

Conclusion

The serum levels of MIF, MBP, and BDNF in TBI patients were positively correlated with the severity of the disease, and MBP, BDNF levels had predictive value in determining patient prognosis.

Kidins220/ARMS modulates brain morphology and anxiety-like traits in adult mice

Kinase D interacting substrate of 220 kDa (Kidins220), also known as ankyrin repeat-rich membrane spanning (ARMS), is a transmembrane scaffold protein that participates in fundamental aspects of neuronal physiology including cell survival, differentiation, and synaptic plasticity. The Kidins220 constitutive knockout line displays developmental defects in the nervous and cardiovascular systems that lead to embryonic lethality, which has so far precluded the study of this protein in the adult. Moreover, Kidins220 mRNA is tightly regulated by alternative splicing, whose impact on nervous system physiology has not yet been addressed in vivo. Here, we have asked to what extent the absence of Kidins220 splicing and the selective knockout of Kidins220 impact on adult brain homeostasis. To answer this question, we used a floxed line that expresses only the full-length, non-spliced Kidins220 mRNA, and a forebrain-specific, CaMKII-Cre driven Kidins220 conditional knockout (cKO) line. Kidins220 cKO brains are characterized by enlarged ventricles in the absence of cell death, and by deficient dendritic arborization in several cortical regions. The deletion of Kidins220 leads to behavioral changes, such as reduced anxiety-like traits linked to alterations in TrkB-BDNF signaling and sex-dependent alterations of hippocampal-dependent spatial memory. Kidins220 floxed mice present similarly enlarged brain ventricles and increased associative memory. Thus, both the absolute levels of Kidins220 expression and its splicing pattern are required for the correct brain development and related expression of behavioral phenotypes. These findings are relevant in light of the increasing evidence linking mutations in the human KIDINS220 gene to the onset of severe neurodevelopmental disorders.

First person – Fanny Jaudon and Martina Albini

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Fanny Jaudon and Martina Albini are co-first authors on ‘ A developmental stage- and Kidins220-dependent switch in astrocyte responsiveness to brain-derived neurotrophic factor’, published in JCS. Fanny is a postdoc at the University of Trieste in the lab of Lorenzo A. Cingolani at Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Genova, Italy, investigating the molecular mechanisms controlling development and function of neuronal circuits and implementing genome-editing approaches for the treatment of neurological disorders. Martina is a PhD student at the Istituto Italiano di Tecnologia in the lab of Fabio Benfenati and Fabrizia Cesca investigating neurotrophin biology and its involvement in neurological diseases.