Expression of the tyrosine kinase discoidin domain receptor 1 (DDR1) in human central nervous system myelin

Functional Role of DDR1 in Oligodendrocyte Signaling Mechanism in Association with Myelination and Remyelination Process in the Central Nerve System

ABSTRACT

Multiple sclerosis (MS) is a complicated, inflammatory disease that causes demyelination of the central nervous system (CNS), resulting in a variety of neurological abnormalities. Over the past several decades, different animal models have been used to replicate the clinical symptoms and neuropathology of MS. The experimental model of experimental autoimmune/allergic encephalomyelitis (EAE) and viral and toxin-induced model was widely used to investigate the clinical implications of MS. Discoidin domain receptor 1 (DDR1) signaling in oligodendrocytes (OL) brings a new dimension to our understanding of MS pathophysiology. DDR1 is effectively involved in the OL during neurodevelopment and remyelination. It has been linked to many cellular processes, including migration, invasion, proliferation, differentiation, and adhesion. However, the exact functional involvement of DDR1 in developing OL and myelinogenesis in the CNS remains undefined. In this review, we critically evaluate the current literature on DDR1 signaling in OL and its proliferation, migration, differentiation, and myelination mechanism in OL in association with the progression of MS. It increases our knowledge of DDR1 in OL as a novel target molecule for oligodendrocyte-associated diseases in the CNS, including MS.

Processing speed mediates the relationship between DDR1 and psychosocial functioning in euthymic patients with bipolar disorder presenting psychotic symptoms

The DDR1 locus is associated with the diagnosis of schizophrenia and with processing speed in patients with schizophrenia and first-episode psychosis. Here, we investigated whether DDR1 variants are associated with bipolar disorder (BD) features. First, we performed a case‒control association study comparing DDR1 variants between patients with BD and healthy controls. Second, we performed linear regression analyses to assess the associations of DDR1 variants with neurocognitive domains and psychosocial functioning. Third, we conducted a mediation analysis to explore whether neurocognitive impairment mediated the association between DDR1 variants and psychosocial functioning in patients with BD. Finally, we studied the association between DDR1 variants and white matter microstructure. We did not find any statistically significant associations in the case‒control association study; however, we found that the combined genotypes rs1264323AA-rs2267641AC/CC were associated with worse neurocognitive performance in patients with BD with psychotic symptoms. In addition, the combined genotypes rs1264323AA-rs2267641AC/CC were associated with worse psychosocial functioning through processing speed. We did not find correlations between white matter microstructure abnormalities and the neurocognitive domains associated with the combined genotypes rs1264323AA-rs2267641AC/CC. Overall, the results suggest that DDR1 may be a marker of worse neurocognitive performance and psychosocial functioning in patients with BD, specifically those with psychotic symptoms.

Coexpression network analysis of the adult brain sheds light on the pathogenic mechanism of DDR1 in schizophrenia and bipolar disorder

DDR1 has been linked to schizophrenia (SCZ) and bipolar disorder (BD) in association studies. DDR1 encodes 58 distinct transcripts, which can be translated into five isoforms (DDR1a-e) and are expressed in the brain. However, the transcripts expressed in each brain cell type, their functions and their involvement in SCZ and BD remain unknown. Here, to infer the processes in which DDR1 transcripts are involved, we used transcriptomic data from the human brain dorsolateral prefrontal cortex of healthy controls (N = 936) and performed weighted gene coexpression network analysis followed by enrichment analyses. Then, to explore the involvement of DDR1 transcripts in SCZ (N = 563) and BD (N = 222), we studied the association of coexpression modules with disease and performed differential expression and transcript significance analyses. Some DDR1 transcripts were distributed across five coexpression modules identified in healthy controls (MHC). MHC1 and MHC2 were enriched in the cell cycle and proliferation of astrocytes and OPCs; MHC3 and MHC4 were enriched in oligodendrocyte differentiation and myelination; and MHC5 was enriched in neurons and synaptic transmission. Most of the DDR1 transcripts associated with SCZ and BD pertained to MHC1 and MHC2. Altogether, our results suggest that DDR1 expression might be altered in SCZ and BD via the proliferation of astrocytes and OPCs, suggesting that these processes are relevant in psychiatric disorders.

Evidence That DDR1 Promotes Oligodendrocyte Differentiation during Development and Myelin Repair after Injury

Oligodendrocytes generate myelin sheaths vital for the formation, health, and function of the central nervous system. Mounting evidence suggests that receptor tyrosine kinases (RTKs) are crucial for oligodendrocyte differentiation and myelination in the CNS. It was recently reported that discoidin domain receptor 1 (Ddr1), a collagen-activated RTK, is expressed in oligodendrocyte lineage. However, its specific expression stage and functional role in oligodendrocyte development in the CNS remain to be determined. In this study, we report that Ddr1 is selectively upregulated in newly differentiated oligodendrocytes in the early postnatal CNS and regulates oligodendrocyte differentiation and myelination. Ddr1 knock-out mice of both sexes displayed compromised axonal myelination and apparent motor dysfunction. Ddr1 deficiency alerted the ERK pathway, but not the AKT pathway in the CNS. In addition, Ddr1 function is important for myelin repair after lysolecithin-induced demyelination. Taken together, the current study described, for the first time, the role of Ddr1 in myelin development and repair in the CNS, providing a novel molecule target for the treatment of demyelinating diseases.

Cross-sectional and longitudinal assessment of the association between DDR1 variants and processing speed in patients with early psychosis and healthy controls

Recent evidence indicates that DDR1 participates in myelination and that variants of DDR1 are associated with decreased cognitive processing speed (PS) in schizophrenia (SZ). Here, we explored whether DDR1 variants were associated with PS in subjects diagnosed with an early psychosis (EP), a condition often preceding SZ. Data from two Spanish independent samples (from Reus and Santander) including patients with EP (n = 75 and n = 312, respectively) and healthy controls (HCs; n = 57 and n = 160) were analyzed. The Trail Making Test part A was used to evaluate PS. Participants underwent genotyping to identify DDR1 variants rs1264323 and rs2267641. Cross-sectional data were analyzed with general linear models and longitudinal data were analyzed using mixed models. We examined the combined rs1264323AA-rs2267641AC/CC genotypes (an SZ-risk combination) on PS. The SZ-risk combined genotypes were associated with increased PS in EP patients but not in HCs in the cross-sectional analysis. In the longitudinal analysis, the SZ-risk combined genotypes were significantly associated with increased PS in both HCs and EP patients throughout the 10-year follow-up but no genotype × time interaction was observed. These results provide further evidence that DDR1 is involved in cognition and should be replicated with other samples.

DDR1 and Its Ligand, Collagen IV, Are Involved in In Vitro Oligodendrocyte Maturation

Discoidin domain receptor 1 (DDR1) is a tyrosine kinase receptor expressed in epithelial cells from different tissues in which collagen binding activates pleiotropic functions. In the brain, DDR1 is mainly expressed in oligodendrocytes (OLs), the function of which is unclear. Whether collagen can activate DDR1 in OLs has not been studied. Here, we assessed the expression of DDR1 during in vitro OL differentiation, including collagen IV incubation, and the capability of collagen IV to induce DDR1 phosphorylation. Experiments were performed using two in vitro models of OL differentiation: OLs derived from adult rat neural stem cells (NSCs) and the HOG16 human oligodendroglial cell line. Immunocytofluorescence, western blotting, and ELISA were performed to analyze these questions. The differentiation of OLs from NSCs was addressed using oligodendrocyte transcription factor 2 (Olig2) and myelin basic protein (MBP). In HOG16 OLs, collagen IV induced DDR1 phosphorylation through slow and sustained kinetics. In NSC-derived OLs, DDR1 was found in a high proportion of differentiating cells (MBP+/Olig2+), but its protein expression was decreased in later stages. The addition of collagen IV did not change the number of DDR1+/MBP+ cells but did accelerate OL branching. Here, we provide the first demonstration that collagen IV mediates the phosphorylation of DDR1 in HOG16 cells and that the in vitro co-expression of DDR1 and MBP is associated with accelerated branching during the differentiation of primary OLs.

Discoidin domain receptor regulates ensheathment, survival and caliber of peripheral axons

Most invertebrate axons and small-caliber axons in mammalian peripheral nerves are unmyelinated but still ensheathed by glia. Here, we use Drosophila wrapping glia to study the development and function of non-myelinating axon ensheathment, which is poorly understood. Selective ablation of these glia from peripheral nerves severely impaired larval locomotor behavior. In an in vivo RNA interference screen to identify glial genes required for axon ensheathment, we identified the conserved receptor tyrosine kinase Discoidin domain receptor (Ddr). In larval peripheral nerves, loss of Ddr resulted in severely reduced ensheathment of axons and reduced axon caliber, and we found a strong dominant genetic interaction between Ddr and the type XV/XVIII collagen Multiplexin (Mp), suggesting that Ddr functions as a collagen receptor to drive axon wrapping. In adult nerves, loss of Ddr decreased long-term survival of sensory neurons and significantly reduced axon caliber without overtly affecting ensheathment. Our data establish essential roles for non-myelinating glia in nerve development, maintenance and function, and identify Ddr as a key regulator of axon-glia interactions during ensheathment and establishment of axon caliber.

Nilotinib modulates LPS-induced cognitive impairment and neuroinflammatory responses by regulating P38/STAT3 signaling

BACKGROUND

In chronic myelogenous leukemia, reciprocal translocation between chromosome 9 and chromosome 22 generates a chimeric protein, Bcr-Abl, that leads to hyperactivity of tyrosine kinase-linked signaling transduction. The therapeutic agent nilotinib inhibits Bcr-Abl/DDR1 and can cross the blood-brain barrier, but its potential impact on neuroinflammatory responses and cognitive function has not been studied in detail.

METHODS

The effects of nilotinib in vitro and in vivo were assessed by a combination of RT-PCR, real-time PCR, western blotting, ELISA, immunostaining, and/or subcellular fractionation. In the in vitro experiments, the effects of 200 ng/mL LPS or PBS on BV2 microglial cells, primary microglia or primary astrocytes pre- or post-treated with 5 µM nilotinib or vehicle were evaluated. The in vivo experiments involved wild-type mice administered a 7-day course of daily injections with 20 mg/kg nilotinib (i.p.) or vehicle before injection with 10 mg/kg LPS (i.p.) or PBS.

RESULTS

In BV2 microglial cells, pre- and post-treatment with nilotinib altered LPS-induced proinflammatory/anti-inflammatory cytokine mRNA levels by suppressing AKT/P38/SOD2 signaling. Nilotinib treatment also significantly downregulated LPS-stimulated proinflammatory cytokine levels in primary microglia and primary astrocytes by altering P38/STAT3 signaling. Experiments in wild-type mice showed that nilotinib administration affected LPS-mediated microglial/astroglial activation in a brain region-specific manner in vivo. In addition, nilotinib significantly reduced proinflammatory cytokine IL-1β, IL-6 and COX-2 levels and P38/STAT3 signaling in the brain in LPS-treated wild-type mice. Importantly, nilotinib treatment rescued LPS-mediated spatial working memory impairment and cortical dendritic spine number in wild-type mice.

CONCLUSIONS

Our results indicate that nilotinib can modulate neuroinflammatory responses and cognitive function in LPS-stimulated wild-type mice.

Discoidin domain receptor 1 as a promising biomarker for high-grade gliomas

Background

Two fundamental challenges in the current therapeutic approach for central nervous system tumors are the tumor heterogeneity and the absence of specific treatments and biomarkers that selectively target the tumor tissue. Therefore, we aimed to investigate the potential relationship between discoidin domain receptor 1 (DDR1) expression and the prognosis and characteristics of glioma patients.

Materials and Methods

Tissue and serum samples from 34 brain tumor patients were evaluated for DDR1 messenger ribonucleic acid levels in comparison to 10 samples from the control group, and Kaplan-Meier survival analysis has performed.

Results

DDR1 expression was observed in both tissue and serum samples of the patient and control groups. DDR1 expression levels in tissue and serum samples from patients were higher in comparison to the control group, although not statistically significant (P > 0.05). A significant correlation between tumor size and DDR1 serum measurements at the level of 0.370 was reported (r = 0.370; P = 0.034). The levels of DDR1 in serum showed a positive correlation with the increasing size of tumor. The results of the 5-year survival analysis depending on the DDR1 tissue levels showed a significantly higher survival rate (P = 0.041) for patients who have DDR1 tissue levels above cutoff value.

Conclusions

DDR1 expression was significantly higher among brain tumor tissues and serum samples and its levels showed a positive correlation with the increased size of tumor. This study can be a starting point, since it investigated and indicated, for the first time, that DDR1 can be a novel therapeutic and prognostic target for aggressive high-grade gliomas.

Coexpression of the discoidin domain receptor 1 gene with oligodendrocyte-related and schizophrenia risk genes in the developing and adult human brain

BACKGROUND

Discoidin domain receptor tyrosine kinase 1 (DDR1) is present in multiple types of epithelial cells and is highly expressed in the nervous system. Previous studies have revealed that DDR1 is involved in schizophrenia (SCZ). Although the expression of DDR1 in oligodendrocytes has been described, its role in brain myelination is not well understood. In this study, we aimed to explore the coexpression network of DDR1 in the human brain and to compare the list of DDR1 coexpressing genes with the list of genes containing single nucleotide polymorphisms (SNPs) that are associated with SCZ.

MATERIALS AND METHODS

We used a weighted gene coexpression network analysis (WGCNA) of a dataset from four brain areas (the dorsolateral prefrontal cortex, primary motor cortex, hippocampus, and striatum) and from four different intervals (I) of life (I-1 = 10-38 weeks postconception, I-2 ≥0 to < 6 years, I-3 ≥ 6 to < 40 years, and I-4 ≥ 40 years of age). We compared the list of genes that are associated with SCZ in the GWAS Catalog with the list of genes coexpressing with DDR1 in each interval.

RESULTS

Our study revealed that DDR1 was coexpressed with oligodendrocyte-related genes mainly in I-2 (adjP = 5.66e-24) and I-3 (adjP = 2.8e-114), which coincided with the coexpression of DDR1 with myelination-related genes (adjP = 9.04e-03 and 2.51e-08, respectively). DDR1 was also coexpressed with astrocyte-related genes in I-1 (adjP = 1.11e-71), I-2 (adjP = 2.12e-20) and I-4 (adjP = 9.93e-52) and with type 2 microglia-related genes in I-1 (adjP = 2.84e-08), I-2 (adjP = 5.68e-16) and I-4 (adjP = 3.66e-10). Moreover, we observed significant enrichment of SCZ susceptibility genes within the coexpression modules containing DDR1 in I-1 and I-4 (P = 1e-04 and 0.0037, respectively), during which the DDR1 module showed the highest association with the astrocytes.

CONCLUSIONS

Our study confirmed that DDR1 is coexpressed with oligodendrocyte- and myelin-related genes in the human brain but suggests that DDR1 may contribute mainly to SCZ risk through its role in other glial cell types, such as astrocytes.

DDR1 methylation is associated with bipolar disorder and the isoform expression and methylation of myelin genes

Aim: To investigate DDR1 methylation in the brains of bipolar disorder (BD) patients and its association with DDR1 mRNA levels and comethylation with myelin genes. Materials & methods: Genome-wide profiling of DNA methylation (Infinium MethylationEPIC BeadChip) corrected for glial composition and DDR1 gene expression analysis in the occipital cortices of individuals with BD (n = 15) and healthy controls (n = 15) were conducted. Results: DDR1 5-methylcytosine levels were increased and directly associated with DDR1b mRNA expression in the brains of BD patients. We also observed that DDR1 was comethylated with a group of myelin genes. Conclusion: DDR1 is hypermethylated in BD brain tissue and is associated with isoform expression. Additionally, DDR1 comethylation with myelin genes supports the role of this receptor in myelination.

Leukocyte and brain DDR1 hypermethylation is altered in psychosis and is correlated with stress and inflammatory markers

Aim: To investigate DDR1 methylation in blood and brain DNA in psychosis and its relationship with stress markers. Materials & methods: Saliva cortisol, blood neutrophil and lymphocyte counts, leukocyte DNA and psychological variables were collected from 60 patients with nonaffective psychosis and 40 healthy controls (HC). Brain dorsolateral prefrontal cortex DNA from 35 patients with schizophrenia and 34 HC was studied. DDR1 methylation at 43 CpG sites was measured using the MassARRAY EpiTYPER platform. Results: We describe leukocyte DDR1 hypermethylation in patients with psychosis compared with HC; this hypermethylation is associated with psychological stress, neutrophil-to-lymphocyte ratios, and, in the dorsolateral prefrontal cortex, DDR1 methylation correlated with DDR1 isoform expression. Conclusion: We confirmed a relationship between stress and blood and brain DDR1 methylation in psychosis.

Multikinase Abl/DDR/Src Inhibition Produces Optimal Effects for Tyrosine Kinase Inhibition in Neurodegeneration

Background and objectives

Inhibition of Abelson (Abl) tyrosine kinase as a therapeutic target has been gaining attention in neurodegeneration. Post-mortem Alzheimer’s and Parkinson’s disease brains show that the levels of several other tyrosine kinases, including Discoidin Domain Receptors (DDR1/2) are elevated. Knockdown of these tyrosine kinases with shRNA reduces neurotoxic proteins, including alpha-synuclein, beta-amyloid and tau.

Methods

Direct profiling of the pharmacokinetics of multi-kinase inhibitors Nilotinib, Bosutinib, Bafetinib, Radotinib and LCB-03-0110 shows differential levels of brain penetration but the ability of these agents to reduce toxic proteins is independent of brain concentration and selectivity to Abl.

Results

Our results indicate that the effective dose of Nilotinib has the lowest plasma:brain ratio (1%) followed by Bosutinib and Radotinib (5%), Bafetinib (12%) and LCB-03-0110 (12%). However, similar doses of multi-kinase Abl/DDR inhibitor Nilotinib, DDR/Src inhibitor LCB-03-0110 and Abl/Src inhibitor Bosutinib were much more effective than the more selective Abl inhibitors Radotinib and Bafetinib. Taken together, these data suggest that a multi-kinase target that includes Abl and other tyrosine kinases (DDRs, and Src) may offer more advantages alleviating neurodegenerative pathologies than the absolute CNS drug concentration and selectivity to Abl.

Conclusion

DDRs and Src are other potential co-targets with Abl in neurodegeneration.

Electronic supplementary material

The online version of this article (10.1007/s40268-019-0266-z) contains supplementary material, which is available to authorized users.

An Analysis of Cellular Communication Network Factor Proteins as Candidate Mediators of Postpartum Psychosis Risk

Postpartum (or puerperal) psychosis (PP) is a severe psychiatric condition associated with hallucinations, delusions, cognitive disorganization, and mood problems, which affects approximately 1-2 out of every 1,000 mothers shortly after childbirth. While the risk factors for, and co-morbidities of, PP are relatively well-defined, currently, the pathophysiology underlying the disorder is very poorly-specified. Here, I argue, on the basis of multiple lines of new evidence, that altered expression of the Cellular Communication Network (CCN) factor proteins (and of the heterodimerizing CCN2 and CCN3 proteins in particular), may be associated with, and possibly causal for, increased PP risk. Future preclinical and clinical studies should aim to test this hypothesis as empirical support for it would provide much-needed clues regarding the biological substrates of PP, and could point to predictive biomarkers for the condition.

Expression of DDR1 in the CNS and in myelinating oligodendrocytes

Discoidin domain receptor 1 (DDR1) is a tyrosine kinase receptor that is activated by fibrillar collagens. Here, we review the expression and role of DDR1 in the central nervous system (CNS). In a murine model, DDR1 is expressed in oligodendrocytes in the developing brain and during remyelination. In human adult brain tissue, DDR1 is detected in a similar pattern as other classical myelin proteins such as myelin basic protein (MBP). Up to 50 transcripts of DDR1 have been detected in human tissues, of which 5 isoforms have been identified. In the human brain, all 5 isoforms are detectable, but DDR1b is the most highly expressed, and DDR1c is coexpressed with myelin genes. DDR1 sequence variants have been associated with psychiatric disorders, and upregulation of this gene occurs in gliomas. Moreover, mutations in DDR1 have been found in tumors of Schwann cells, which are the myelinating cells of the peripheral nervous system. All these data suggest that DDR1 plays a role in myelination and is relevant to neuropsychiatric diseases.

Discoidin domain receptor 1 gene variants are associated with decreased white matter fractional anisotropy and decreased processing speed in schizophrenia

DDR1 has been linked to schizophrenia (SZ) and myelination. Here, we tested whether DDR1 variants in people at risk for SZ influence white matter (WM) structural variations and cognitive processing speed (PS). First, following a case-control design (Study 1), SZ patients (N = 1193) and controls (N = 1839) were genotyped for rs1264323 and rs2267641 at DDR1, and the frequencies were compared. We replicated the association between DDR1 and SZ (rs1264323, adjusted P = 0.015). Carriers of the rs1264323AA combined with the rs2267641AC or CC genotype are at risk to develop SZ compared to the other genotype combinations. Second, SZ patients (Study 2, N = 194) underwent an evaluation of PS using the Trail Making Test (TMT) and DDR1 genotyping. To compare PS between DDR1 genotype groups, we conducted an analysis of covariance (including rs1264323 as a covariate) and found that SZ patients with the rs2267641CC genotype had decreased PS compared to patients with the AA and AC genotypes. Third, 54 patients (Study 3) from Study 2 were selected based on rs1264323 genotype to undergo reevaluation, including a DTI-MRI brain scan. To test for associations between PS, WM microstructure and DDR1 genotype, we first localized those WM regions where fractional anisotropy (FA) was correlated with PS and tested whether FA showed differences between the rs1264323 genotypes. SZ patients with the rs1264323AA genotype showed decreased FA in WM regions associated with decreased PS. We conclude that DDR1 variants may confer a risk of SZ through WM microstructural alterations leading to cognitive dysfunction.

Do Defective Immune System-Mediated Myelination Processes Increase Postpartum Psychosis Risk?

Postpartum (or puerperal) psychosis (PP) is a rare, severe psychiatric disorder that affects women shortly after childbirth; risk is particularly high in individuals with a history of bipolar disorder or PP, but the underlying pathophysiology remains poorly understood. Emerging evidence suggests that immune system (dys)function plays an important role in disorder onset. On the basis of new findings from clinical and animal model studies, we hypothesise that the abundance and/or activity of regulatory T cells, and the efficacy of consequent (re)myelination processes in the brain mediated by CCN proteins, is perturbed in PP; this pathway may be modulated by risk and protective/treatment factors for the disorder, and identifying abnormalities within it could signpost novel predictive biomarkers and therapeutic targets.

Discoidin domain receptor inhibition reduces neuropathology and attenuates inflammation in neurodegeneration models

The role of cell surface tyrosine kinase collagen-activated receptors known as discoidin domain receptors (DDRs) is unknown in neurodegenerative diseases. We detect up-regulation in DDRs level in post-mortem Alzheimer and Parkinson brains. Lentiviral shRNA knockdown of DDR1 and DDR2 reduces the levels of α-synuclein, tau, and β-amyloid and prevents cell loss in vivo and in vitro. DDR1 and DDR2 knockdown alters brain immunity and significantly reduces the level of triggering receptor expressed on myeloid cells (TREM)-2 and microglia. These studies suggest that DDR1 and DDR2 inhibition is a potential target to clear neurotoxic proteins and reduce inflammation in neurodegeneration.

Understanding the pathophysiology of postpartum psychosis: Challenges and new approaches

Postpartum psychosis is a severe psychiatric condition which affects 1-2 of every 1000 mothers shortly after childbirth. Whilst there is convincing evidence that the condition is precipitated by a complex combination of biological and environmental factors, as yet the pathophysiological mechanisms remain extremely poorly defined. Here, I critically review approaches that have been, or are being, employed to identify and characterise such mechanisms; I also review a recent animal model approach, and describe a novel biological risk model that it suggests. Clarification of biological risk mechanisms underlying disorder risk should permit the identification of relevant predictive biomarkers which will ensure that “at risk” subjects receive prompt clinical intervention if required.

Collagen Fibril Ultrastructure in Mice Lacking Discoidin Domain Receptor 1

The quantity and quality of collagen fibrils in the extracellular matrix (ECM) have a pivotal role in dictating biological processes. Several collagen-binding proteins (CBPs) are known to modulate collagen deposition and fibril diameter. However, limited studies exist on alterations in the fibril ultrastructure by CBPs. In this study, we elucidate how the collagen receptor, discoidin domain receptor 1 (DDR1) regulates the collagen content and ultrastructure in the adventitia of DDR1 knock-out (KO) mice. DDR1 KO mice exhibit increased collagen deposition as observed using Masson's trichrome. Collagen ultrastructure was evaluated in situ using transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Although the mean fibril diameter was not significantly different, DDR1 KO mice had a higher percentage of fibrils with larger diameter compared with their wild-type littermates. No significant differences were observed in the length of D-periods. In addition, collagen fibrils from DDR1 KO mice exhibited a small, but statistically significant, increase in the depth of the fibril D-periods. Consistent with these observations, a reduction in the depth of D-periods was observed in collagen fibrils reconstituted with recombinant DDR1-Fc. Our results elucidate how DDR1 modulates collagen fibril ultrastructure in vivo, which may have important consequences in the functional role(s) of the underlying ECM.

Transcriptome sequencing and genome-wide association analyses reveal lysosomal function and actin cytoskeleton remodeling in schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe mental disorders with high heritability. Clinicians have long noticed the similarities of clinic symptoms between these disorders. In recent years, accumulating evidence indicates some shared genetic liabilities. However, what is shared remains elusive. In this study, we conducted whole transcriptome analysis of post-mortem brain tissues (cingulate cortex) from SCZ, BPD and control subjects, and identified differentially expressed genes in these disorders. We found 105 and 153 genes differentially expressed in SCZ and BPD, respectively. By comparing the t-test scores, we found that many of the genes differentially expressed in SCZ and BPD are concordant in their expression level (q⩽0.01, 53 genes; q⩽0.05, 213 genes; q⩽0.1, 885 genes). Using genome-wide association data from the Psychiatric Genomics Consortium, we found that these differentially and concordantly expressed genes were enriched in association signals for both SCZ (P<10(-7)) and BPD (P=0.029). To our knowledge, this is the first time that a substantially large number of genes show concordant expression and association for both SCZ and BPD. Pathway analyses of these genes indicated that they are involved in the lysosome, Fc gamma receptor-mediated phagocytosis, regulation of actin cytoskeleton pathways, along with several cancer pathways. Functional analyses of these genes revealed an interconnected pathway network centered on lysosomal function and the regulation of actin cytoskeleton. These pathways and their interacting network were principally confirmed by an independent transcriptome sequencing data set of the hippocampus. Dysregulation of lysosomal function and cytoskeleton remodeling has direct impacts on endocytosis, phagocytosis, exocytosis, vesicle trafficking, neuronal maturation and migration, neurite outgrowth and synaptic density and plasticity, and different aspects of these processes have been implicated in SCZ and BPD.

DDR1 may play a key role in destruction of the blood-brain barrier after cerebral ischemia-reperfusion

Discoidin domain receptor 1 (DDR1) has been shown to mediate matrix metalloproteinase-9 (MMP-9) secretions and degrade all extracellular matrix compounds in mammalian tumor cells. We hypothesized that DDR1 expression will be elevated and the blood-brain barrier (BBB) will be damaged after focal cerebral ischemia in rats. Inhibiting DDR1 expression can alleviate BBB disruption and cerebral ischemic damage via down-regulation of MMP-9 expression and activity. To test our hypothesis, we injected specific DDR1 siRNA into ipsilateral ischemic lateral ventricles in a focal ischemic model. Our results showed that phospho-DDR1 expression increased after ischemia/reperfusion (I/R) injury (p < 0.01). Inactivation of DDR1 by specific siRNA caused a decrease in phospho-DDR1 and MMP-9 expression in the ischemic cortex, reduced stroke-induced infarct volume, and alleviated BBB disruption in rat brain following I/R injury (p < 0.01). Our results suggested that DDR1-siRNA attenuates phospho-DDR1 and MMP-9 upregulation, which was followed by a reduction in infarction and BBB disruption in the ischemic brain after I/R injury. DDR1 may represent a molecular target for the prevention of BBB disruption after cerebral I/R injury.

Postnatal growth of the human pons: a morphometric and immunohistochemical analysis

Despite its critical importance to global brain function, the postnatal development of the human pons remains poorly understood. In the present study, we first performed magnetic resonance imaging (MRI)-based morphometric analyses of the postnatal human pons (0-18 years; n = 6-14/timepoint). Pons volume increased 6-fold from birth to 5 years, followed by continued slower growth throughout childhood. The observed growth was primarily due to expansion of the basis pontis. T2-based MRI analysis suggests that this growth is linked to increased myelination, and histological analysis of myelin basic protein in human postmortem specimens confirmed a dramatic increase in myelination during infancy. Analysis of cellular proliferation revealed many Ki67(+) cells during the first 7 months of life, particularly during the first month, where proliferation was increased in the basis relative to tegmentum. The majority of proliferative cells in the postnatal pons expressed the transcription factor Olig2, suggesting an oligodendrocyte lineage. The proportion of proliferating cells that were Olig2(+) was similar through the first 7 months of life and between basis and tegmentum. The number of Ki67(+) cells declined dramatically from birth to 7 months and further decreased by 3 years, with a small number of Ki67(+) cells observed throughout childhood. In addition, two populations of vimentin/nestin-expressing cells were identified: a dorsal group near the ventricular surface, which persists throughout childhood, and a parenchymal population that diminishes by 7 months and was not evident later in childhood. Together, our data reveal remarkable postnatal growth in the ventral pons, particularly during infancy when cells are most proliferative and myelination increases.

Mitochondrial DNA (mtDNA) in brain samples from patients with major psychiatric disorders: gene expression profiles, mtDNA content and presence of the mtDNA common deletion

Several lines of evidence support a mitochondrial dysfunction in major psychiatric disorders. The objective of this study was to determine whether mitochondrial DNA (mtDNA) expression or content are implicated in the mitochondrial dysfunction observed in schizophrenia (SCH), bipolar disorder (BD), and major depressive disorder (MDD). MtDNA gene expression and mtDNA content (including the MT-ND4 deletion) were measured by RT-qPCR and qPCR, respectively. Post-mortem brain tissue from 60 subjects, divided evenly into four diagnostic groups (SCH, BD, MDD, and control (C)), was analyzed. MT-ND1 gene expression was significantly increased in the BD group compared with the C group. MDD and SCH patients showed a similar pattern of mtDNA expression, which was different from that in BD patients. Similarly, a larger number of MDD and SCH patients tended to have the MT-ND4 gene deleted compared with BD and C subjects. However, no other significant differences were observed in mtDNA gene expression and mtDNA content. Notably, high variability was observed in the mtDNA gene expression and content in each diagnostic group. Previous studies and the present work provide evidence for a role of mtDNA in SCH, BD and MDD. However, further studies with larger patient and control groups as well as by analyzing distinct brain regions are needed to elucidate the role of mtDNA in major psychiatric disorders.

Discoidin domain receptors guide axons along longitudinal tracts in C. elegans

Discoidin domain receptors are a family of receptor tyrosine kinases activated by collagens. Here we characterize the role of the two discoidin domain receptors, ddr-1 and ddr-2, of the nematode C. elegans during nervous system development. ddr-2 mutant animals exhibit axon guidance defects in major longitudinal tracts most prominently in the ventral nerve cord. ddr-1 mutants show no significant phenotype on their own but significantly enhance guidance defects of ddr-2 in double mutants. ddr-1 and ddr-2 GFP-reporter constructs are expressed in neurons with axons in all affected nerve tracts. DDR-1 and DDR-2 GFP fusion proteins localize to axons. DDR-2 is required cell-autonomously in the PVPR neuron for the guidance of the PVPR pioneer axon, which establishes the left ventral nerve cord tract and serves as substrate for later outgrowing follower axons. Our results provide the first insight on discoidin domain receptor function in invertebrates and establish a novel role for discoidin domain receptors in axon navigation and axon tract formation.

The discoidin domain receptor 1 gene has a functional A2RE sequence

Discoidin domain receptor 1 (DDR1) is expressed in myelin oligodendrocytes and co-localizes with myelin basic protein (MBP). Alternative splicing of DDR1 generates five isoforms designated DDR1a-e. The MBP mRNA contains an hnRNP A2 response element (A2RE) sequence that is recognized by heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1, which is responsible for transport of the MBP mRNA to oligodendrocyte processes. We hypothesized that DDR1 could have a functional A2RE sequence. By in silico analysis, we identified an A2RE-like sequence in the human DDR1 mRNA. We observed nuclear and dendrite cytoplasmic immunofluorescence, indicating that DDR1 and hnRNP A2/B1 co-localize in human oligodendrocytes and in differentiated HOG16 cells. The A2RE-like sequence of DDR1 contains the single nucleotide polymorphism rs2267641, and we found that in the human brain, the minor allele is associated with lower and higher levels DDR1b and DDR1c mRNA expression, respectively. Moreover, a positive correlation between DDR1c and the myelin genes myelin-associated glycoprotein and oligodendrocyte lineage transcription factor 2 was found. Differentiated HOG16 cells transfected with an hnRNP A2/B1 siRNA simultaneously show a decrease and an increase in the DDR1c and DDR1b mRNA expression levels, respectively, which was accompanied by a decrease in DDR1 protein levels at the cytoplasmic edges. These results suggest that the DDR1 A2RE sequence is functionally involved in the hnRNP A2/B1-mediated splicing and transport of the DDR1c mRNA.

Fetal hypoxia and programming of matrix metalloproteinases

Fetal hypoxia adversely affects the brain and heart development, yet the mechanisms responsible remain elusive. Recent studies indicate an important role of the extracellular matrix in fetal development and tissue remodeling. The matrix metalloproteinases (MMPs) and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs) have been implicated in a variety of physiological and pathological processes in the cardiovascular and central nervous systems. This review summarizes current knowledge of the mechanisms by which fetal hypoxia induces the imbalance of MMPs, TIMPs and collagen expression patterns, resulting in growth restriction and aberrant tissue remodeling in the developing heart and brain. Collectively, this information could lead to the development of preventive diagnoses and therapeutic strategies in the fetal programming of cardiovascular and neurological disorders.