Identification and characterization of a long isoform of human IFT80, IFT80-L

The Effect of IFT80 Deficiency in Osteocytes on Orthodontic Loading-Induced and Physiologic Bone Remodeling: In Vivo Study

Osteocytes are the main mechanosensory cells during orthodontic and physiologic bone remodeling. However, the question of how osteocytes transmit mechanical stimuli to biological responses remains largely unanswered. Intraflagellar transport (IFT) proteins are important for the formation and function of cilia, which are proposed to be mechanical sensors in osteocytes. In particular, IFT80 is highly expressed in mouse skulls and essential for ciliogenesis. This study aims to investigate the short- and long-term effects of IFT80 deletion in osteocytes on orthodontic bone remodeling and physiological bone remodeling in response to masticatory force. We examined 10-week-old experimental DMP1 CRE+.IFT80f/f and littermate control DMP1 CRE-.IFT80f/f mice. After 5 and 12 days of orthodontic force loading, the orthodontic tooth movement distance and bone parameters were evaluated using microCT. Osteoclast formation was assessed using TRAP-stained paraffin sections. The expression of sclerostin and RANKL was examined using immunofluorescence stain. We found that the deletion of IFT80 in osteocytes did not significantly impact either orthodontic or physiologic bone remodeling, as demonstrated by similar OTM distances, osteoclast numbers, bone volume fractions (bone volume/total volume), bone mineral densities, and the expressions of sclerostin and RANKL. Our findings suggest that there are other possible mechanosensory systems in osteocytes and anatomic limitations to cilia deflection in osteocytes in vivo.

The CTNNBIP1-CLSTN1 fusion transcript regulates human neocortical development

Fusion transcripts or RNAs have been found in both disordered and healthy human tissues and cells; however, their physiological functions in the brain development remain unknown. In the analysis of deposited RNA-sequence libraries covering early to middle embryonic stages, we identify 1,055 fusion transcripts present in the developing neocortex. Interestingly, 98 fusion transcripts exhibit distinct expression patterns in various neural progenitors (NPs) or neurons. We focus on CTNNBIP1-CLSTN1 (CTCL), which is enriched in outer radial glial cells that contribute to cortex expansion during human evolution. Intriguingly, downregulation of CTCL in cultured human cerebral organoids causes marked reduction in NPs and precocious neuronal differentiation, leading to impairment of organoid growth. Furthermore, the expression of CTCL fine-tunes Wnt/β-catenin signaling that controls cortex patterning. Together, this work provides evidence indicating important roles of fusion transcript in human brain development and evolution.

TRIM59, amplified in ovarian cancer, promotes tumorigenesis through the MKP3/ERK pathway

Tripartite motif containing 59 (TRIM59) functions as an oncoprotein in various human cancers including ovarian cancer. In this study, we found that TRIM59 gene amplification was prevalent in ovarian cancer tissues, and its amplification was significantly correlated with poorer overall survival. Moreover, knockdown of TRIM59 in SKOV3 and OVCAR3 cells, which had relatively high level of TRIM59, suppressed glucose uptake and lactate production. TRIM59 knockdown also decreased the expression of c-Myc and lactate dehydrogenase A, and the phosphorylation of extracellular signal-regulated kinase (ERK). TRIM59 overexpression in A2780 cells, which expressed low level of TRIM59, showed reverse effects. Notably, treatment with an ERK inhibitor (PD98059) completely abolished the oncogenic effects of TRIM59 overexpression. Interestingly, TRIM59 increased the ubiquitination of MAP kinase phosphatase 3 (MKP3), which may dephosphorylate and inactivate ERK. Ectopic expression of MKP3 inhibited the promoting effects of TRIM59 on glycolysis and the phosphorylation of ERK. TRIM59 protein expression was negatively correlated with MKP3 protein expression in ovarian cancer tissues. Finally, TRIM59 amplification potently affected the anticancer effect of 3-bromopyruvate, an inhibitor of glycolysis, in ovarian cancer cells and patient-derived xenograft. In conclusion, these results suggest that TRIM59 may regulate glycolysis in ovarian cancer via the MKP3/ERK pathway.

TRIM13 is a negative regulator of MDA5-mediated type I interferon production

Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are essential intracellular detectors of viral RNA. They contribute to the type I interferon (IFN) response that is crucial for host defense against viral infections. Given the potent antiviral and proinflammatory activities elicited by the type I IFNs, induction of the type I IFN response is tightly regulated. Members of the tripartite motif (TRIM) family of proteins have recently emerged as key regulators of antiviral immunity. We show that TRIM13, an E3 ubiquitin ligase, is expressed in immune cells and is upregulated in bone marrow-derived macrophages upon stimulation with inducers of type I IFN. TRIM13 interacts with MDA5 and negatively regulates MDA5-mediated type I IFN production in vitro, acting upstream of IFN regulatory factor 3. We generated Trim13(-/-) mice and show that upon lethal challenge with encephalomyocarditis virus (EMCV), which is sensed by MDA5, Trim13(-/-) mice produce increased amounts of type I IFNs and survive longer than wild-type mice. Trim13(-/-) murine embryonic fibroblasts (MEFs) challenged with EMCV or poly(I · C) also show a significant increase in beta IFN (IFN-β) levels, but, in contrast, IFN-β responses to the RIG-I-detected Sendai virus were diminished, suggesting that TRIM13 may play a role in positively regulating RIG-I function. Together, these results demonstrate that TRIM13 regulates the type I IFN response through inhibition of MDA5 activity and that it functions nonredundantly to modulate MDA5 during EMCV infection.

IMPORTANCE

The type I interferon (IFN) response is crucial for host defense against viral infections, and proper regulation of this pathway contributes to maintaining immune homeostasis. Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are intracellular detectors of viral RNA that induce the type I IFN response. In this study, we show that expression of the gene tripartite motif 13 (Trim13) is upregulated in response to inducers of type I IFN and that TRIM13 interacts with both MDA5 and RIG-I in vitro. Through the use of multiple in vitro and in vivo model systems, we show that TRIM13 is a negative regulator of MDA5-mediated type I IFN production and may also impact RIG-I-mediated type I IFN production by enhancing RIG-I activity. This places TRIM13 at a key junction within the viral response pathway and identifies it as one of the few known modulators of MDA5 activity.

The intraflagellar transport protein IFT80 is required for cilia formation and osteogenesis

Intraflagellar transport (IFT) proteins are essential for the assembly and maintenance of cilia, which play important roles in development and homeostasis. IFT80 is a newly defined IFT protein. Partial mutation of IFT80 in humans causes diseases such as Jeune asphyxiating thoracic dystrophy (JATD) and short rib polydactyly (SRP) type III with abnormal skeletal development. However, the role and mechanism of IFT80 in osteogenesis is unknown. Here, we first detected IFT80 expression pattern and found that IFT80 was highly expressed in mouse long bone, skull, and during osteoblast differentiation. By using lentivirus-mediated RNA interference (RNAi) technology to silence IFT80 in murine mesenchymal progenitor cell line-C3H10T1/2 and bone marrow derived stromal cells, we found that silencing IFT80 led to either shortening or loss of cilia and the decrease of Arl13b expression - a small GTPase that is localized in cilia. Additionally, silencing IFT80 blocked the expression of osteoblast markers and significantly inhibited ALP activity and cell mineralization. We further found that IFT80 silencing inhibited the expression of Gli2, a critical transcriptional factor in the hedgehog signaling pathway. Overexpression of Gli2 rescued the deficiency of osteoblast differentiation from IFT80-silenced cells, and dramatically promoted osteoblast differentiation. Moreover, introduction of Smo agonist (SAG) promotes osteoblast differentiation, which was partially inhibited by IFT80 silencing. Thus, these results suggested that IFT80 plays an important role in osteogenesis through regulating Hedgehog/Gli signal pathways.

Clinical insights gained from eight new cases and review of reported cases with Jeune syndrome (asphyxiating thoracic dystrophy)

Jeune syndrome, originally described as asphyxiating thoracic dystrophy by Jeune et al. [Jeune et al. (1955); Arch Fr Pediatr 12:886-891], is an autosomal recessive osteochondrodysplasia with characteristic skeletal abnormalities, and variable renal, hepatic, pancreatic, and retinal complications. We present eight patients, including two brothers with Jeune syndrome, and an extensive review of 118 cases in the published literature with the purposes of: (1) defining the clinical and radiological diagnostic criteria for Jeune syndrome; (2) comparing our cases to those in the literature meeting the documented clinical and radiological findings of Jeune syndrome, in order to: (3) provide an accurate clinical characterization of Jeune syndrome with frequency of associated complications and outcome data. In order to estimate the frequency of phenotypic abnormalities in Jeune syndrome as precisely as possible, we did not include reports in the literature with incomplete descriptions of the radiologic and clinical findings, nor those reports having additional findings overlapping with other syndromes. We found that the occurrence of renal, hepatic, and ophthalmologic complications is variable; does not correlate with severity of the skeletal phenotype; nor is it predictable even with the presence of a well-defined skeletal phenotype, as in this study. Based upon these cases with Jeune syndrome, renal and hepatic abnormalities occur in approximately 30% of cases, with renal failure occurring in 38% of those with kidney involvement. Eye abnormalities are reported in 15%, but it is unclear whether this represents under-ascertainment. There is a 1.2:1 ratio between living and deceased patients; a respiratory cause of death is most common, occurring almost exclusively in those less than 2 years of age, and a renal etiology accounts for all deaths between the ages of 3-10 years of age. There is a paucity of affected individuals reported in the literature greater than age 20 years, and a lack of longitudinal data to obtain accurate data on morbidity and mortality of Jeune syndrome at older ages. This study provides a well-defined group of patients with Jeune syndrome with delineation of the frequency of associated findings, which may form a basis for current and future genotype-phenotype studies.

Ciliopathy spectrum expanded? Jeune syndrome associated with foregut dysmotility and malrotation

We report the association and surgical management of gastrointestinal dysmotility and malrotation with Jeune asphyxiating thoracic dystrophy (JATD), an autosomal recessive condition that often results in respiratory failure due to a small rib cage. A 4-month-old male with JATD presented with vomiting and aspiration pneumonitis compounding already severe respiratory morbidity. A contrast study revealed esophageal and gastric dysmotility with associated malrotation. This was treated surgically with good results. Some cases of JATD are caused by missense mutations in the gene IFT80, which encodes a protein implicated in the process of intraflagellar transport of primary cilia. We speculate that these abdominal complications might also be part of the extending spectrum of ciliopathy.