Integrin-mediated mechanotransduction.

Cells can detect and react to the biophysical properties of the extracellular environment through integrin-based adhesion sites and adapt to the extracellular milieu in a process called mechanotransduction. At these adhesion sites, integrins connect the extracellular matrix (ECM) with the F-actin cytoskeleton and transduce mechanical forces generated by the actin retrograde flow and myosin II to the ECM through mechanosensitive focal adhesion proteins that are collectively termed the "molecular clutch." The transmission of forces across integrin-based adhesions establishes a mechanical reciprocity between the viscoelasticity of the ECM and the cellular tension. During mechanotransduction, force allosterically alters the functions of mechanosensitive proteins within adhesions to elicit biochemical signals that regulate both rapid responses in cellular mechanics and long-term changes in gene expression. Integrin-mediated mechanotransduction plays important roles in development and tissue homeostasis, and its dysregulation is often associated with diseases.

Indian hedgehog mutations causing brachydactyly type A1 impair Hedgehog signal transduction at multiple levels.

Brachydactyly type A1 (BDA1), the first recorded Mendelian autosomal dominant disorder in humans, is characterized by a shortening or absence of the middle phalanges. Heterozygous missense mutations in the Indian Hedgehog (IHH) gene have been identified as a cause of BDA1; however, the biochemical consequences of these mutations are unclear. In this paper, we analyzed three BDA1 mutations (E95K, D100E, and E131K) in the N-terminal fragment of Indian Hedgehog (IhhN). Structural analysis showed that the E95K mutation changes a negatively charged area to a positively charged area in a calcium-binding groove, and that the D100E mutation changes the local tertiary structure. Furthermore, we showed that the E95K and D100E mutations led to a temperature-sensitive and calcium-dependent instability of IhhN, which might contribute to an enhanced intracellular degradation of the mutant proteins via the lysosome. Notably, all three mutations affected Hh binding to the receptor Patched1 (PTC1), reducing its capacity to induce cellular differentiation. We propose that these are common features of the mutations that cause BDA1, affecting the Hh tertiary structure, intracellular fate, binding to the receptor/partners, and binding to extracellular components. The combination of these features alters signaling capacity and range, but the impact is likely to be variable and mutation-dependent. The potential variation in the signaling range is characterized by an enhanced interaction with heparan sulfate for IHH with the E95K mutation, but not the E131K mutation. Taken together, our results suggest that these IHH mutations affect Hh signaling at multiple levels, causing abnormal bone development and abnormal digit formation.

Missense mutations in IHH impair Indian Hedgehog signaling in C3H10T1/2 cells: Implications for brachydactyly type A1, and new targets for Hedgehog signaling.

Heterozygous missense mutations in IHH result in Brachydactyly type A1 (BDA1; OMIM 112500), a condition characterized by the shortening of digits due to hypoplasia/aplasia of the middle phalanx. Indian Hedgehog signaling regulates the proliferation and differentiation of chondrocytes and is essential for endochondral bone formation. Analyses of activated IHH signaling in C3H10T1/2 cells showed that three BDA1-associated mutations (p.E95K, p.D100E and p.E131K) severely impaired the induction of targets such as Ptch1 and Gli1. However, this was not a complete loss of function, suggesting that these mutations may affect the interaction with the receptor PTCH1 or its partners, with an impact on the induction potency. From comparative microarray expression analyses and quantitative real-time PCR, we identified three additional targets, Sostdc1, Penk1 and Igfbp5, which were also severely affected. Penk1 and Igfbp5 were confirmed to be regulated by GLI1, while the induction of Sostdc1 by IHH is independent of GLI1. SOSTDC1 is a BMP antagonist, and altered BMP signaling is known to affect digit formation. The role of Penk1 and Igfbp5 in skeletogenesis is not known. However, we have shown that both Penk1 and Igfbp5 are expressed in the interzone region of the developing joint of mouse digits, providing another link for a role for IHH signaling in the formation of the distal digits.

Transcription factor SP4 is a susceptibility gene for bipolar disorder.

The Sp4 transcription factor plays a critical role for both development and function of mouse hippocampus. Reduced expression of the mouse Sp4 gene results in a variety of behavioral abnormalities relevant to human psychiatric disorders. The human SP4 gene is therefore examined for its association with both bipolar disorder and schizophrenia in European Caucasian and Chinese populations respectively. Out of ten SNPs selected from human SP4 genomic locus, four displayed significant association with bipolar disorder in European Caucasian families (rs12668354, p = 0.022; rs12673091, p = 0.0005; rs3735440, p = 0.019; rs11974306, p = 0.018). To replicate the genetic association, the same set of SNPs was examined in a Chinese bipolar case control sample. Four SNPs displayed significant association (rs40245, p = 0.009; rs12673091, p = 0.002; rs1018954, p = 0.001; rs3735440, p = 0.029), and two of them (rs12673091, rs3735440) were shared with positive SNPs from European Caucasian families. Considering the genetic overlap between bipolar disorder and schizophrenia, we extended our studies in Chinese trios families for schizophrenia. The SNP7 (rs12673091, p = 0.012) also displayed a significant association. The SNP7 (rs12673091) was therefore significantly associated in all three samples, and shared the same susceptibility allele (A) across all three samples. On the other hand, we found a gene dosage effect for mouse Sp4 gene in the modulation of sensorimotor gating, a putative endophenotype for both schizophrenia and bipolar disorder. The deficient sensorimotor gating in Sp4 hypomorphic mice was partially reversed by the administration of dopamine D2 antagonist or mood stabilizers. Both human genetic and mouse pharmacogenetic studies support Sp4 gene as a susceptibility gene for bipolar disorder or schizophrenia. The studies on the role of Sp4 gene in hippocampal development may provide novel insights for the contribution of hippocampal abnormalities in these psychiatric disorders.

No association found between the promoter variants of ADRA1A and schizophrenia in the Chinese population.

Schizophrenia is a chronic psychiatry disorder with a strong genetic component. A recent association study of alpha(1A)-adrenoceptor gene (ADRA1A) involving an isolated Spanish population, focusing on the promoter region of the ADRA1A, genotyped eight single SNPs at the promoter region of ADRA1A and found that two SNPs, -563G/A and -9625G/A, were associated with schizophrenia and schizoaffective disorders. We were interested in the two positive sites reported and selected five variants among the promoter region of ADRA1A, namely -563G/A, -9625G/A, -2760C/A, -4155G/C and a new substitution we detected between -508bp and -530bp upstream of the translation initiation site. Our sample consisted of 480 schizophrenia and 480 control subjects. All recruits were Han Chinese in Shanghai origin. However, neither individual SNP nor any haplotype was associated with schizophrenia in our study. These results suggest that the variants among the promoter of ADRA1A gene are unlikely to play a major role in the susceptibility to schizophrenia in the Chinese population.

Lack of association between three serotonin genes and suicidal behavior in Chinese psychiatric patients.

BACKGROUND: Suicide is a significant health problem throughout the world. The serotoninergic system is believed to be involved in suicidal behavior and there is evidence of biological abnormalities of two serotonin receptors (HTR2A, HTR2C) and one serotonin transporter (5HTT) in suicide victims. Rs6313 (T102C) of HTR2A and rs6318 (Cys23Ser) of HTR2C have been investigated in suicide behavior in other studies. METHODS: Here, we investigated rs6313 and rs6318 and other 10 randomly chosen SNPs, of those three genes in a study of 329 psychiatric patients who had never attempted suicide and 297 patients who had attempted suicide. RESULTS: No associations were found for the 12 SNPS. CONCLUSIONS: Our results do not support the involvement of HTR2A, 5HTT or HTR2C in suicidal behavior in Han Chinese subjects.

IHH and FGF8 coregulate elongation of digit primordia.

In the developing limb bud, digit pattern arises from anterior-posterior (A-P) positional information which is provided by the concentration gradient of SHH. However, the mechanisms of translating early asymmetry into morphological form are still unclear. Here, we examined the ability of IHH and FGF8 signaling to regulate digital chondrogenesis, by implanting protein-loaded beads in the interdigital space singly and in combination. We found that IHH protein induced an elongated digit and that FGF8 protein blocked the terminal phalange formation. Molecular marker analysis showed that IHH expanded Sox9 expression in mesenchymal cells possibly through up-regulated FGF8 expression. Application of both IHH and FGF8 protein induced a large terminal phalange. These results suggest that both enhanced IHH and FGF8 signaling are required for the development of additional cartilage element in limbs. IHH and FGF8 maybe play different roles and act synergistically to promote chondrogenesis during digit primordia elongation.

A case-control association study between the GRID1 gene and schizophrenia in the Chinese Northern Han population.

The glutamatergic dysfunction hypothesis of schizophrenia implicates the genes involved in glutamatergic transmission as strong candidates for schizophrenia-susceptibility. Recent linkage and association studies have identified the glutamate receptor, ionotropic, delta 1 gene GRID1 on 10q22 as a strong candidate for schizophrenia. In this current association study, we genotyped five genetic variants within the GRID1 gene in 567 Chinese Han subjects recruited from Northeast of China (260 schizophrenics and 307 normal controls). Four SNPs, rs1902666 (P=0.024), rs2814351 (P=0.027), rs11591408 (P=0.0000107) and rs999383 (P=0.000093) were found to be significantly associated with schizophrenia. Haplotype analysis also revealed significance with global P values of 0.0081 and 0.00076 for SNPs 1-2 and SNPs 3-4-5 haplotypes, respectively. Our results strongly support previously reported association studies, implicating GRID1 in the etiology of schizophrenia.

Functional variants in the promoter region of Chitinase 3-like 1 (CHI3L1) and susceptibility to schizophrenia.

The chitinase 3-like 1 gene (CHI3L1) is abnormally expressed in the hippocampus of subjects with schizophrenia and may be involved in the cellular response to various environmental events that are reported to increase the risk of schizophrenia. Here, we provide evidence that the functional variants at the CHI3L1 locus influence the genetic risk of schizophrenia. First, using case-control and transmission/disequilibrium-test (TDT) methodologies, we detected a significant association between schizophrenia and haplotypes within the promoter region of CHI3L1 in two independent cohorts of Chinese individuals. Second, the at-risk CCC haplotype (P=.00058 and .0018 in case-control and TDT studies, respectively) revealed lower transcriptional activity (P=2.2 x 10(-7)) and was associated with lower expression (P=3.1 x 10(-5)) compared with neutral and protective haplotypes. Third, we found that an allele of SNP4 (rs4950928), the tagging SNP of CCC, impaired the MYC/MAX-regulated transcriptional activation of CHI3L1 by altering the transcriptional-factor consensus sequences, and this may be responsible for the decreased expression of the CCC haplotype. In contrast, the protective TTG haplotype was associated with a high level of CHI3L1 expression. Our findings identify CHI3L1 as a potential schizophrenia-susceptibility gene and suggest that the genes involved in the biological response to adverse environmental conditions are likely to play roles in the predisposition to schizophrenia.

RGS4 polymorphisms and risk of schizophrenia: an association study in Han Chinese plus meta-analysis.

Recently, several researches based on expression analysis, genetic linkage and association studies have suggested that the regulator of G-protein signaling 4 (RGS4) might be a schizophrenia susceptibility gene. However, these linkage and association studies have been conducted using different ethnic samples, and have therefore tended to produce inconsistent results. To help to clarify this inconsistency, we used non-family based samples to carry out a case-control analysis on six single nucleotide polymorphisms (SNPs) (including four widely investigated SNPs, SNP1, 4, 7, 18 and another two SNPs, rs2842030 and rs2344671) in a Chinese Han sample set comprising 288 schizophrenia patients and 288 normal controls. All genotypings were conducted by direct sequencing and all SNPs were in Hardy-Weinberg equilibrium. We found no individual SNPs or haplotypes to be associated with schizophrenia. We also performed a meta-analysis based on all published population-based association studies on the topic including our own. The results of both our case-control study in the Chinese Han population and the meta-analysis yield no significant evidence for association, which suggests that the genetic polymorphisms within RGS4 are unlikely to confer an increased susceptibility to the etiology of schizophrenia.

No genetic association between polymorphisms in the AMPA receptor subunit GluR4 gene (GRIA4) and schizophrenia in the Chinese population.

The glutamatergic dysfunction hypothesis of schizophrenia suggests genes involved in glutamatergic transmission as candidates for schizophrenia-susceptibility genes. It has recently been reported that some haplotypes in the AMPA receptor subunit GluR4 Gene (GRIA4), which is located on chromosome 11q22, are positively associated with schizophrenia in the Japanese population. In order to assess the role of GRIA4 in schizophrenia, we examined three reported positive SNPs (single nucleotide polymorphisms): rs609239, rs641574 and rs659840 at the GRIA4 locus in schizophrenic cases (n = 372) and controls (n = 392) of the Chinese population. Although we had observed similar allele and genotype frequencies compared with that in the Japanese population, no evidence was found for association with the disease in the analysis of either single nucleotide polymorphisms (all P-values > 0.300) or haplotype relative risk (all P-values > 0.088). Our results suggest that the three SNPs of GRIA4 are unlikely to play a major role in the susceptibility to schizophrenia in the Chinese population.