Novel Kidins220/ARMS Splice Isoforms: Potential Specific Regulators of Neuronal and Cardiovascular Development

Alterations in KIDINS220/ARMS Expression Impact Sensory Processing and Social Behavior in Adult Mice

Kinase D-interacting substrate of 220 kDa (Kidins220) is a transmembrane protein that participates in neural cell survival, maturation, and plasticity. Mutations in the human KIDINS220 gene are associated with a neurodevelopmental disorder ('SINO' syndrome) characterized by spastic paraplegia, intellectual disability, and in some cases, autism spectrum disorder. To better understand the pathophysiology of KIDINS220-linked pathologies, in this study, we assessed the sensory processing and social behavior of transgenic mouse lines with reduced Kidins220 expression: the CaMKII-driven conditional knockout (cKO) line, lacking Kidins220 in adult forebrain excitatory neurons, and the Kidins220floxed line, expressing constitutively lower protein levels. We show that alterations in Kidins220 expression levels and its splicing pattern cause impaired response to both auditory and olfactory stimuli. Both transgenic lines show impaired startle response to high intensity sounds, with preserved pre-pulsed inhibition, and strongly reduced social odor recognition. In the Kidins220floxed line, olfactory alterations are associated with deficits in social memory and increased aggressive behavior. Our results broaden our knowledge of the SINO syndrome; understanding sensory information processing and its deviations under neuropathological conditions is crucial for devising future therapeutic strategies to enhance the quality of life of affected individuals.

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.

Prenatal delineation of a distinct lethal fetal syndrome caused by a homozygous truncating KIDINS220 variant

Kinase D-interacting substrate of 220 kDa (KIDINS220) is a transmembrane protein playing integral role in growth mediating pathways in the nervous and cardiovascular systems. KIDINS220 heterozygous truncating variants that affect the protein's C-terminus have been associated with a phenotype, so far described only in few unrelated children, including spastic paraplegia, intellectual disability, nystagmus, and obesity. More recently, a homozygous, more N-terminal truncating variant in KIDINS220 gene was suggested to be associated with enlarged cerebral ventricles and limb contractures in three fetuses from a consanguineous family. We confirm the latter finding by presenting the first detailed prenatal identification of a fetal phenotype associated with novel homozygous deleterious frameshift variant in KIDINS220 gene in a consanguineous healthy Egyptian couple. History of unexplained seven miscarriages and a similar stillbirth were recorded. Prenatal ultrasonography revealed limb contractions and ventriculomegaly; in addition to previously unreported cerebellar anomalies, cardiac anomalies and hydrops fetalis. These findings represent an expansion of clinical and molecular spectrum associated with KIDINS220 variants and broaden our understanding of genotype-phenotype relationships in lethal congenital contractures syndromes and associated severe abnormal embryological development. More generally, our study adds KIDINS220 to the rare group of genes which may cause disease by either of two distinct mutational mechanisms.

Differential regulation of Kidins220 isoforms in Huntington's disease

Huntington's disease (HD) is an inherited progressive neurodegenerative disease characterized by brain atrophy particularly in the striatum that produces motor impairment, and cognitive and psychiatric disturbances. Multiple pathogenic mechanisms have been proposed including dysfunctions in neurotrophic support and calpain-overactivation, among others. Kinase D-interacting substrate of 220 kDa (Kidins220), also known as ankyrin repeat-rich membrane spanning (ARMS), is an essential mediator of neurotrophin signaling. In adult brain, Kidins220 presents two main isoforms that differ in their carboxy-terminal length and critical protein-protein interaction domains. These variants are generated through alternative terminal exon splicing of the conventional exon 32 (Kidins220-C32) and the recently identified exon 33 (Kidins220-C33). The lack of domains encoded by exon 32 involved in key neuronal functions, including those controlling neurotrophin pathways, pointed to Kidins220-C33 as a form detrimental for neurons. However, the functional role of Kidins220-C33 in neurodegeneration or other pathologies, including HD, has not been explored. In the present work, we discover an unexpected selective downregulation of Kidins220-C33, in the striatum of HD patients, as well as in the R6/1 HD mouse model starting at early symptomatic stages. These changes are C33-specific as Kidins220-C32 variant remains unchanged. We also find the early decrease in Kidins220-C33 levels takes place in neurons, suggesting an unanticipated neuroprotective role for this isoform. Finally, using ex vivo assays and primary neurons, we demonstrate that Kidins220-C33 is downregulated by mechanisms that depend on the activation of the protease calpain. Altogether, these results strongly suggest that calpain-mediated Kidins220-C33 proteolysis modulates onset and/or progression of HD.

From Neural Crest Development to Cancer and Vice Versa: How p75NTR and (Pro)neurotrophins Could Act on Cell Migration and Invasion?

The p75 neurotrophin receptor (p75^NTR), also known as low-affinity nerve growth factor, belongs to the tumor necrosis factor family of receptors. p75^NTR is widely expressed in the nervous system during the development, as well as, in the neural crest population, since p75^NTR has been described as ubiquitously expressed and considered as a neural crest marker. Neural crest cells (NCCs) constitute an transient population accurately migrating and invading, with precision, defined sites of the embryo. During migration, NCCs are guided along distinct migratory pathways by specialized molecules present in the extracellular matrix or on the surfaces of those cells. Two main processes direct NCC migration during the development: (1) an epithelial-to-mesenchymal transition and (2) a process known as contact inhibition of locomotion. In adults, p75^NTR remains expressed by NCCs and has been identified in an increasing number of cancer cells. Nonetheless, the regulation of the expression of p75^NTR and the underlying mechanisms in stem cell biology or cancer cells have not yet been sufficiently addressed. The main objective of this review is therefore to analyze elements of our actual knowledge regarding p75^NTR roles during the development (mainly focusing on neural crest development) and see how we can transpose that information from development to cancer (and vice versa) to better understand the link between p75^NTR and cell migration and invasion. In this review, we successively analyzed the molecular mechanisms of p75^NTR when it interacts with several coreceptors and/or effectors. We then analyzed which signaling pathways are the most activated or linked to NCC migration during the development. Regarding cancer, we analyzed the described molecular pathways underlying cancer cell migration when p75^NTR was correlated to cancer cell migration and invasion. From those diverse sources of information, we finally summarized potential molecular mechanisms underlying p75^NTR activation in cell migration and invasion that could lead to new research areas to develop new therapeutic protocols.

Homozygous KIDINS220 loss-of-function variants in fetuses with cerebral ventriculomegaly and limb contractures

Heterozygous mutations in KIDINS220 were recently suggested a cause of spastic paraplegia, intellectual disability, nystagmus and obesity. All patients carried terminal nonsense de novo mutations that seemed to escape nonsense-mediated mRNA decay. The mechanism for pathogenicity is yet unexplained, as it seems that heterozygous loss-of-function variants of KIDINS220 are generally well tolerated. We present a consanguineous couple who experienced four pregnancy terminations due to repeated findings in the fetuses comprising enlarged cerebral ventricles and limb contractures. Exome sequencing in two of the aborted fetuses revealed a shared homozygous frameshift variant in exon 24 in KIDINS220. Sanger sequencing of the variant in available family members showed complete segregation with the affection status, resulting in a LOD score of 2.5 under an autozygous inheritance model. mRNA studies revealed destruction of the original splice site, resulting in an out-of-frame transcript and introduction of a premature termination codon in exon 25. Premature termination codons in this position are likely to cause activation of nonsense-mediated mRNA decay and result in complete absence of KIDINS220 protein in individuals homozygous for the variant. The phenotype of the presented fetuses overlaps with findings in functional studies of knockout Kidins220 mice embryos that are non-viable with enlarged cerebral ventricles. The human fetuses also exhibit several similarities to the milder phenotype described in patients with heterozygous KIDINS220 mutations. We hence propose that the identified homozygous loss-of-function variant in KIDINS220 causes the phenotype in the presented fetuses, and that this represents a hitherto undescribed severe autosomal recessive neurodevelopmental disorder.

Functions of the multi-interacting protein KIDINS220/ARMS in cancer and other pathologies

Development of an organ and subsequently the whole system from an embryo is a highly integrated process. Although there is evidence that different systems are interconnected during developmental stages, the molecular understanding of this relationship is either not known or only to a limited extent. Nervous system development, amongst all, is maybe the most crucial and complex process. It relies on the correct distribution of specific neuronal growth factors and hormones to the specific receptors. Among the plethora of proteins that are involved in downstream signalling of neuronal growth factors, we find the kinase-D interacting substrate of 220 kDa (KIDINS220), also known as ankyrin-rich repeat membrane spanning (ARMS) protein. KIDINS220 has been shown to play a substantial role in the nervous system and vascular system development as well as in neuronal survival and differentiation. It serves as a downstream regulator for many important neuronal and vascular growth factors such as vascular endothelial growth factor (VEGF), the neurotrophin family, glutamate receptors and ephrin receptors. Moreover, activation and differentiation of B- and T-cells, as well as tumour cell proliferation has also shown to be related to KIDINS220. This review comprehensively summarises the existing research data on this protein, with a particular interest in its role in cancer and in other pathologies.

Heterozygous KIDINS220/ARMS nonsense variants cause spastic paraplegia, intellectual disability, nystagmus, and obesity

We identified de novo nonsense variants in KIDINS220/ARMS in three unrelated patients with spastic paraplegia, intellectual disability, nystagmus, and obesity (SINO). KIDINS220 is an essential scaffold protein coordinating neurotrophin signal pathways in neurites and is spatially and temporally regulated in the brain. Molecular analysis of patients' variants confirmed expression and translation of truncated transcripts similar to recently characterized alternative terminal exon splice isoforms of KIDINS220 KIDINS220 undergoes extensive alternative splicing in specific neuronal populations and developmental time points, reflecting its complex role in neuronal maturation. In mice and humans, KIDINS220 is alternative spliced in the middle region as well as in the last exon. These full-length and KIDINS220 splice variants occur at precise moments in cortical, hippocampal, and motor neuron development, with splice variants similar to the variants seen in our patients and lacking the last exon of KIDINS220 occurring in adult rather than in embryonic brain. We conducted tissue-specific expression studies in zebrafish that resulted in spasms, confirming a functional link with disruption of the KIDINS220 levels in developing neurites. This work reveals a crucial physiological role of KIDINS220 in development and provides insight into how perturbation of the complex interplay of KIDINS220 isoforms and their relative expression can affect neuron control and human metabolism. Altogether, we here show that de novo protein-truncating KIDINS220 variants cause a new syndrome, SINO. This is the first report of KIDINS220 variants causing a human disease.

Stepping Out of the Shade: Control of Neuronal Activity by the Scaffold Protein Kidins220/ARMS

The correct functioning of the nervous system depends on the exquisitely fine control of neuronal excitability and synaptic plasticity, which relies on an intricate network of protein-protein interactions and signaling that shapes neuronal homeostasis during development and in adulthood. In this complex scenario, Kinase D interacting substrate of 220 kDa/ankyrin repeat-rich membrane spanning (Kidins220/ARMS) acts as a multi-functional scaffold protein with preferential expression in the nervous system. Engaged in a plethora of interactions with membrane receptors, cytosolic signaling components and cytoskeletal proteins, Kidins220/ARMS is implicated in numerous cellular functions including neuronal survival, neurite outgrowth and maturation and neuronal activity, often in the context of neurotrophin (NT) signaling pathways. Recent studies have highlighted a number of cell- and context-specific roles for this protein in the control of synaptic transmission and neuronal excitability, which are at present far from being completely understood. In addition, some evidence has began to emerge, linking alterations of Kidins220 expression to the onset of various neurodegenerative diseases and neuropsychiatric disorders. In this review, we present a concise summary of our fragmentary knowledge of Kidins220/ARMS biological functions, focusing on the mechanism(s) by which it controls various aspects of neuronal activity. We have tried, where possible, to discuss the available evidence in the wider context of NT-mediated regulation, and to outline emerging roles of Kidins220/ARMS in human pathologies.