Soutarou Izumi

Unfolded protein response, activated by OASIS family transcription factors, promotes astrocyte differentiation

OASIS is a member of the CREB/ATF family of transcription factors and modulates cell- or tissue-specific unfolded protein response signalling. Here we show that this modulation has a critical role in the differentiation of neural precursor cells into astrocytes. Cerebral cortices of mice specifically deficient in OASIS (Oasis(-/-)) contain fewer astrocytes and more neural precursor cells than those of wild-type mice during embryonic development. Furthermore, astrocyte differentiation is delayed in primary cultured Oasis(-/-) neural precursor cells. The transcription factor Gcm1, which is necessary for astrocyte differentiation in Drosophila, is revealed to be a target of OASIS. Introduction of Gcm1 into Oasis(-/-) neural precursor cells improves the delayed differentiation of neural precursor cells into astrocytes by accelerating demethylation of the Gfap promoter. Gcm1 expression is temporally controlled by the unfolded protein response through interactions between OASIS family members during astrocyte differentiation. Taken together, our findings demonstrate a novel mechanism by which OASIS and its associated family members are modulated by the unfolded protein response to finely control astrocyte differentiation.

The endoplasmic reticulum stress transducer OASIS is involved in the terminal differentiation of goblet cells in the large intestine

Background: OASIS is an ER stress transducer expressed in the large intestine. Results: Mature goblet cells are decreased in Oasis−/− mice. Knockdown of the Oasis transcript impairs the maturation of goblet cells. Conclusion: OASIS plays crucial roles in terminal differentiation of goblet cells. Significance: The ER stress response mediated by OASIS signaling is involved in cell differentiation and maturation. OASIS is a basic leucine zipper transmembrane transcription factor localized in the endoplasmic reticulum (ER) that is cleaved in its transmembrane region in response to ER stress. This novel ER stress transducer has been demonstrated to express in osteoblasts and astrocytes and promote terminal maturation of these cells. Additionally, OASIS is highly expressed in goblet cells of the large intestine. In this study, we investigated the roles of OASIS in goblet cell differentiation in the large intestine. To analyze the functions of OASIS in goblet cells, we examined morphological changes and the expression of goblet cell differentiation markers in the large intestine of Oasis−/− mice. By disrupting the Oasis gene, the number of goblet cells and production of mucus were decreased in the large intestine. Oasis−/− goblet cells showed abnormal morphology of mucous vesicles and rough ER. The expression levels of mature goblet cell markers were lower, and conversely those of early goblet cell markers were higher in Oasis−/− mice, indicating that differentiation from early to mature goblet cells is impaired in Oasis−/− mice. To determine the association of OASIS with other factors involved in goblet cell differentiation, in vitro experiments using a cell culture model were performed. We found that OASIS was activated in response to mild ER stress that is induced in differentiating goblet cells. Knockdown of the Oasis transcript perturbed goblet cell terminal differentiation. Together, our data indicate that OASIS plays crucial roles in promoting the differentiation of early goblet cells to mature goblet cells in the large intestine.

Activation of OASIS family, ER stress transducers, is dependent on its stabilization

Endoplasmic reticulum (ER) stress transducers transduce signals from the ER to the cytoplasm and nucleus when unfolded proteins accumulate in the ER. BBF2 human homolog on chromosome 7 (BBF2H7) and old astrocyte specifically induced substance (OASIS), ER-resident transmembrane proteins, have recently been identified as novel ER stress transducers that have roles in chondrogenesis and osteogenesis, respectively. However, the molecular mechanisms that regulate the activation of BBF2H7 and OASIS under ER stress conditions remain unresolved. Here, we showed that BBF2H7 and OASIS are notably unstable proteins that are easily degraded via the ubiquitin-proteasome pathway under normal conditions. ER stress conditions enhanced the stability of BBF2H7 and OASIS, and promoted transcription of their target genes. HMG-CoA reductase degradation 1 (HRD1), an ER-resident E3 ubiquitin ligase, ubiquitinated BBF2H7 and OASIS under normal conditions, whereas ER stress conditions dissociated the interaction between HRD1 and BBF2H7 or OASIS. The stabilization of OASIS in Hrd1−/− cells enhanced the expression of collagen fibers during osteoblast differentiation, whereas a knockdown of OASIS in Hrd1−/− cells suppressed the production of collagen fibers. These findings suggest that ER stress stabilizes OASIS family members and this is a novel molecular mechanism for the activation of ER stress transducers.

The Endoplasmic Reticulum Stress Transducer BBF2H7 Suppresses Apoptosis by Activating the ATF5-MCL1 Pathway in Growth Plate Cartilage

Background: The endoplasmic reticulum stress transducer BBF2H7 is expressed in proliferating chondrocytes. Results: Apoptosis is promoted in the cartilage of Bbf2h7−/− mice. BBF2H7 activates Atf5 transcription, followed by apoptosis suppression. Conclusion: BBF2H7 plays crucial roles in suppressing ER stress-induced apoptosis. Significance: BBF2H7 acts as a bifunctional regulator to promote cartilage extracellular matrix protein secretion and inhibit ER stress-induced apoptosis. BBF2H7 (box B-binding factor 2 human homolog on chromosome 7) is a basic leucine zipper transmembrane transcription factor that belongs to the cyclic AMP-responsive element-binding protein (CREB)/activating transcription factor (ATF) family. This novel endoplasmic reticulum (ER) stress transducer is localized in the ER and is cleaved in its transmembrane region in response to ER stress. BBF2H7 has been shown to be expressed in proliferating chondrocytes in cartilage during the development of long bones. The target of BBF2H7 is Sec23a, one of the coat protein complex II components. Bbf2h7-deficient (Bbf2h7−/−) mice exhibit severe chondrodysplasia, with expansion of the rough ER in proliferating chondrocytes caused by impaired secretion of extracellular matrix (ECM) proteins. We observed a decrease in the number of proliferating chondrocytes in the cartilage of Bbf2h7−/− mice. TUNEL staining of the cartilage showed that apoptosis was promoted in Bbf2h7−/− chondrocytes. Atf5 (activating transcription factor 5), another member of the CREB/ATF family and an antiapoptotic factor, was also found to be a target of BBF2H7 in chondrocytes. ATF5 activated the transcription of Mcl1 (myeloid cell leukemia sequence 1), which belongs to the antiapoptotic B-cell leukemia/lymphoma 2 family, to suppress apoptosis. Finally, we found that the BBF2H7-ATF5-MCL1 pathway specifically suppressed ER stress-induced apoptosis in chondrocytes. Taken together, our findings indicate that BBF2H7 is activated in response to ER stress caused by synthesis of abundant ECM proteins and plays crucial roles as a bifunctional regulator to accelerate ECM protein secretion and suppress ER stress-induced apoptosis by activating the ATF5-MCL1 pathway during chondrogenesis.

Transcriptional Regulation of VEGFA by the Endoplasmic Reticulum Stress Transducer OASIS in ARPE-19 Cells

Background Vascular endothelial growth factor-A (VEGFA) is the main mediator of angiogenesis. Angiogenesis plays important roles not only in many physiological processes, but also in the pathophysiology of many diseases. VEGFA is one of the therapeutic targets of treatment for ocular diseases with neovascularization. Therefore, elucidation of the regulatory mechanisms for VEGFA expression is important for the development of pharmaceutical drugs. Recent studies have demonstrated that the unfolded protein response is involved in the transcriptional regulation of VEGFA. However, the precise regulation of VEGFA in the human retina is not fully understood. Principal Findings When human retinal pigment epithelial cells, ARPE-19, were exposed to endoplasmic reticulum stressors, VEGFA mRNA was significantly upregulated. The unfolded protein response-related transcription factors XBP1, ATF4, ATF6, and OASIS were expressed in ARPE-19 cells. To determine which transcription factors preferentially contribute to the induction of VEGFA expression after endoplasmic reticulum stress, we carried out reporter assays using an approximately 6-kbp 5′-upstream region of the human VEGFA gene. Among these transcription factors, OASIS acted most effectively on the VEGFA promoter in ARPE-19 cells. Based on data obtained for certain deleted and mutated reporter constructs, we determined that OASIS promoted VEGFA expression by acting on a cyclic AMP-responsive element-like site located at around –500 bp relative to the VEGFA transcription start site. Furthermore, we confirmed that OASIS directly bound to the promoter region containing this site by chromatin immunoprecipitation assays. Conclusions and Significance We have demonstrated a novel regulatory mechanism for VEGFA transcription by OASIS in human retinal pigment epithelial cells. Chemical compounds that regulate the binding of OASIS to the promoter region of the VEGFA gene may have potential as therapeutic agents for ocular diseases with neovascularization.

The influence of stem offset and neck shaft angles on the range of motion in total hip arthroplasty

PurposeTo evaluate the influence of stem offset and neck shaft angles on the range of motion before component impingement (ROMCI) and bony impingement (ROMBI), and the types of impingement in total hip arthroplasty (THA).MethodsUsing the computed tomography data of 101 patients who underwent THA, three-dimensional dynamic motion analysis was performed using a modular implant (Kinectiv® stem) that enabled adjustment of offset and leg length independently. We defined offset as horizontal offset (HO) and leg length as vertical offset (VO), and measured the ROMCI and ROMBI in flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) with the configuration of each horizontal/vertical offset.ResultsWe found that HO lengthening increased the ROMCI and ROMBI in Flex and Int-R by delaying bony impingement, although excessive lengthening had minimal effect. On the contrary, VO lengthening decreased the ROMCI and ROMBI in Flex and ROMCI in Int-R. As for Ext-R, VO lengthening had positive effects on the ROMCI and ROMBI, whereas lengthening of HO had negative effects on the ROMCI and ROMBI.ConclusionsWe demonstrated that the appropriate long offset with a low shaft angle increased the ROM in Flex and Int-R, and a high neck shaft angle increased the ROM in Ext-R. We should use implants properly in accordance with the types of impingement for avoiding dislocations in THA.

Low femoral antetorsion and total hip arthroplasty: a risk factor

PurposeThe purpose of this study was to evaluate whether femoral antetorsion affects the range of motion (ROM) following total hip arthroplasty (THA) using 3D dynamic analysis.MethodsUsing 3D computed tomography (CT) data of 71 patients (71 hips) who underwent THA, we calculated antetorsion of the femoral neck, flexion range of motion (Flex ROM), internal rotation (Int-R) and external rotation (Ext-R). Evaluation of the relationship between antetorsion, ROM and the impingement site was performed. As for implant position, anteversion of the femoral implant was set to be the same as natural antetorsion of the femoral neck, and the acetabular component was set 45° of total anteversion in all cases.ResultsWe found a significant decrease in Flex ROM and Int-R inversely proportional to femoral antetorsion. In patients with lower antetorsion, Flex ROM and Int-R decreased due to bony impingement (the anterior great trochanteric region of the femur impinges on the anteroinferior edge of the anteroinferior iliac spine). However, in Ext-R, there was no relationship between ROM and femoral antetorsion.ConclusionsWe demonstrated that lower femoral antetorsion substantially affects Flex ROM and Int-R due to bony impingement. For these patients, consideration must be given to retaining femoral anterior offset in THA.

Factors affecting the potential for posterior bony impingement after total hip arthroplasty

Aims Our aim was to evaluate the radiographic characteristics of patients undergoing total hip arthroplasty (THA) for the potential of posterior bony impingement using CT simulations. Patients and Methods Virtual CT data from 112 patients who underwent THA were analysed. There were 40 men and 72 women. Their mean age was 59.1 years (41 to 76). Associations between radiographic characteristics and posterior bony impingement and the range of external rotation of the hip were evaluated. In addition, we investigated the effects of pelvic tilt and the neck/shaft angle and femoral offset on posterior bony impingement. Results The range of external rotation and the ischiofemoral length were significantly lower, while femoral anteversion, the ischial ratio, and ischial angle were significantly higher in patients with posterior bony impingement compared with those who had implant impingement (p < 0.05). The range of external rotation positively correlated with ischiofemoral length (r = 0.49, p < 0.05), and negatively correlated with ischial length (r = ‐0.49, p < 0.05), ischial ratio (r =‐ 0.49, p < 0.05) and ischial angle (r = ‐0.55, p < 0.05). The range of external rotation was lower in patients with posterior pelvic tilt (p < 0.05) and in those with a high offset femoral component (p < 0.05) due to posterior bony impingement. Conclusion Posterior bony impingement after THA is more likely in patients with a wider ischium and a narrow ischiofemoral space. A high femoral offset and posterior pelvic tilt are also risk factors for this type of impingement.

Low femoral antetorsion as a risk factor for bony impingement after bipolar hemiarthroplasty

IntroductionReports of dislocation after bipolar hemiarthroplasty (BHA) abound in literature, and several studies have mentioned the factors that are associated with an increased risk of dislocation. However, there is no report detailing the pattern of impingement in BHA and how femoral antetorsion can affect the range of motion (ROM) after BHA.PurposeThe purpose of this study was to evaluate the pattern of impingement in BHA and whether femoral antetorsion affects the ROM after BHA using three-dimensional (3D) dynamic motion analysis.MethodsUsing the computed tomography (CT) data of 60 patients (60 hips), including 31 men and 29 women who underwent BHA for the treatment of idiopathic osteonecrosis (ION) of the femoral head, we calculated the antetorsion of the femoral neck, ROM of flexion (Flex), internal rotation (Int-R), and external rotation (Ext-R) using a CT-based 3D simulation software. We evaluated the pattern of impingement and the relationship between femoral antetorsion and ROM in BHA. As for the implant position in the 3D simulation software, the anteversion of the femoral implant was set to be the same as the natural antetorsion of the femoral neck and neck length was set to be the standard neck in all cases.ResultsThis study revealed the mechanism of impingement in BHA: (1) bone to bone impingement and (2) implant to bone impingement. We found a significant decrease in the ROM of Flex and Int-R inversely proportional to the femoral antetorsion. In patients with lower femoral antetorsion, the ROM of Flex and Int-R decreased due to bony impingement (the anterior great trochanteric region of the femur impinges on the anteroinferior edge of the anteroinferior iliac spine). Whereas, high anteversion of the femoral implant may decrease the ROM of Ext-R; however, our results also showed that even the lowest ROM of Ext-R with 10° hip extension was over 40°.ConclusionsWe demonstrated that lower femoral antetorsion substantially affects the ROM of Flex and Int-R due to bony impingement. For these patients, there should be consideration given to retaining femoral “anterior offset” in BHA.

The effect of cup medialization and lateralization on hip range of motion in total hip arthroplasty

Background: There is little description of the effect of cup position on the hip range of motion in total hip arthroplasty. The purpose is to evaluate the effect of cup medialization/lateralization with a compensatory increase/decrease in femoral offset on the hip range of motion, and whether the bone morphology of the anterior inferior iliac spine affects hip range of motion in total hip arthroplasty. Methods: Using the CT data of 100 patients (male; 30, female; 70), 3D‐dynamic motion analysis was performed in four scenarios with cup medialization/lateralization with the same/decreased global offset. We calculated the range of motion before component impingement and bony impingement in flexion, internal rotation and external rotation using the software. Furthermore, we measured bony morphological features of anterior inferior iliac spine, and we analyzed the correlations among them. Findings: We found that the cup medialization with the same stem offset had negative effects on hip range of motion in flexion and internal rotation due to bony impingement, whereas cup medialization caused external rotation to significantly decrease with the same global offset. On the other hand, cup lateralization with the same global offset had negative effects on flexion and internal rotation, whereas external rotation increased. Furthermore, there were negative correlations among flexion and laterally large and steep anterior inferior iliac spine. Interpretation: Our results demonstrated that the advantage of cup medialization can depend on the individual anatomy such as bony morphology of anterior inferior iliac spine in flexion. HIGHLIGHTSThe horizontal cup position substantially affects the range of motion after total hip arthroplasty.The stem offset also substantially affects the range of motion in total hip arthroplastyThe advantage of cup medialization depends on the individual anatomy.