Characterization of a Novel Splicing Variant in Acylglycerol Kinase (AGK) Associated with Fatal Sengers Syndrome

Mitochondrial functional integrity depends on protein and lipid homeostasis in the mitochondrial membranes and disturbances in their accumulation can cause disease. AGK, a mitochondrial acylglycerol kinase, is not only involved in lipid signaling but is also a component of the TIM22 complex in the inner mitochondrial membrane, which mediates the import of a subset of membrane proteins. AGK mutations can alter both phospholipid metabolism and mitochondrial protein biogenesis, contributing to the pathogenesis of Sengers syndrome. We describe the case of an infant carrying a novel homozygous AGK variant, c.518+1G>A, who was born with congenital cataracts, pielic ectasia, critical congenital dilated myocardiopathy, and hyperlactacidemia and died 20 h after birth. Using the patient’s DNA, we performed targeted sequencing of 314 nuclear genes encoding respiratory chain complex subunits and proteins implicated in mitochondrial oxidative phosphorylation (OXPHOS). A decrease of 96-bp in the length of the AGK cDNA sequence was detected. Decreases in the oxygen consumption rate (OCR) and the OCR:ECAR (extracellular acidification rate) ratio in the patient’s fibroblasts indicated reduced electron flow through the respiratory chain, and spectrophotometry revealed decreased activity of OXPHOS complexes I and V. We demonstrate a clear defect in mitochondrial function in the patient’s fibroblasts and describe the possible molecular mechanism underlying the pathogenicity of this novel AGK variant. Experimental validation using in vitro analysis allowed an accurate characterization of the disease-causing variant.

Downregulation of acylglycerol kinase suppresses high glucose-induced endothelial-mesenchymal transition in HRECs through regulating the LPAR1/TGF-β/Notch signaling pathway

The endothelial-mesenchymal transition (EndMT) participates in the progression of diabetic retinopathy (DR), but cell-intrinsic factors modulating this process remain elusive. In this study, we explored the role of lysophosphatidic acid (LPA)-producing enzyme, acylglycerol kinase (AGK) in the EndMT of human retinal microvascular endothelial cells (HRECs) under high glucose (HG) conditions. We found that AGK was significantly elevated in HG-treated cells. In addition, AGK knockdown reversed the HG-induced EndMT in HRECs, which was evidenced by the increased epithelial markers (CD31 and VE-cadherin) and decreased mesenchymal markers (FSP1 and α-SMA). Furthermore, downregulation of AGK inhibited the HG-induced activation of TGF-β/Notch pathways, whereas exogenous TGF-β1 (10 ng/ml) impeded the inhibitory effects of AGK knockdown on HG-induced EndMT in HRECs. Additionally, the silence of AGK abolished the HG-induced upregulation of LPA and its receptor LPAR1, and overexpression of LPAR1 further rescued the AGK knockdown-mediated inhibition of the EndMT process. In conclusion, we demonstrate that downregulation of acylglycerol kinase suppresses high glucose-induced endothelial-mesenchymal transition in HRECs through regulating the LPAR1/TGF-β/Notch signaling pathway, indicating that AGK might be a potential therapeutic target for the treatment of DR.

Acylglycerol Kinase-Targeted Therapies in Oncology

Acylglycerol kinase (AGK) is a recently discovered mitochondrial lipid kinase, and mutation of its gene is the fundamental cause of Sengers syndrome. AGK is not only involved in the stability of lipid metabolism but also closely related to mitochondrial protein transport, glycolysis, and thrombocytopoiesis. Evidence indicates that AGK is an important factor in the occurrence and development of tumors. Specifically, AGK has been identified as an oncogene that partakes in the regulation of tumor cell growth, invasion, metastasis, and drug resistance. The versatility of AGK and its unique role in different types of cancerous and normal cells greatly piqued our interest. We believe that AGK is a promising target for cancer therapy. Therefore, this review summarizes the main research advances concerning AGK, including the discovery of its physiological/pathogenic mechanisms, and provides a reference for the feasible evaluation of AGK as a therapeutic target for human diseases, particularly tumors.

P–422 Acylglycerol Kinase is a new novel marker in preeclampsia

Study question What is the potential function of Acylglycerol Kinase (AGK) in the pathogenesis of preeclampsia(PE). Summary answer AGK plays an important role in the pathogenesis of PE by influencing the function of the trophoblast cells. What is known already PE is the leading cause of maternal and perinatal mortality and morbidity. The underlying mechanism is still not completely elucidated. Disorder migration, invasion and mitochondria function of trophoblast cells are one of mechanism in preeclampsia. AGK is a subunit of the mitochondrial channel protein complex TIM22, and maintain the stability of mitochondrial structure and function. Studies have shown that AGK is related to the development of various cancers by infecting the cells migration and invasion. It will be interesting to explore the potential function of AGK in the process of early trophoblast development and the pathogenesis of PE. Study design, size, duration Firstly, explore the expression of AGK in PE. Secondly, lentivirus systems was used to generate loss and gain of function models in trophoblast cell line-HTR8/Sneov to study the role of AGK in the pathogenesis of PE. Participants/materials, setting, methods We examined the expression of AGK both in placental tissues from PE patients and normal pregnant patients. Meanwhile, we generated AGK loss and gain of function models in HTR8/Sneov cells by using lentivirus systems. Transwell assays, scratch-wound assays, EDU and plate clone formation assays, cell apoptosis assays, cell cycle assays, ATP concentration, mtDNA level and transmission electron microscopy were used to examine the function of AGK in HTR8/Sneov cells model. Main results and the role of chance In this study, AGK was significantly decreased in the extra-villous trophoblast (EVT) cells in placental tissues of PE patients compared with that in control group by immunohistochemistry. And further confirmed the expression of AGK in placental tissues by QPCR, western blot. We demonstrated that knockdown of AGK in HTR8 dramatically decreased the cell proliferation, migration and invasion. It also showed the significantly lower plate clone formation rate in AGK knockdown -HTR8 cells compare with the WT HTR8 cells. While overexpression of AGK in HTR8 dramatically increased the cell proliferation, migration, invasion and higher plate clone formation rate. Further, we demonstrated that AGK regulated the ATP level and mtDNA level in HTR8 cells model. And we found that knockdown AGK decreased the number of mitochondria, and shown the mitochondrial crista disorder, mitochondrial swelling and dissolution and mitochondrial membrane fragmentation. While overexpression AGK increased the number of mitochondria. Limitations, reasons for caution Although we show that AGK played an important role in the function of HTR8, the study of working mechanism of AGK in PE is still very limited. More studies will be performed to explore its underline mechanism. Wider implications of the findings: This study was the first time to explore the role of AGK in PE. It will help us to better understand the pathogenesis of PE, which might be helpful in future application of novel therapeutic targets in PE. Trial registration number Not applicable

Case Report: Two Chinese Infants of Sengers Syndrome Caused by Mutations in AGK Gene

Sengers syndrome (OMIM #212350) is a rare autosomal recessive disorder due to mutations in acylglycerol kinase (AGK) gene. We report two cases that were diagnosed clinically and confirmed genetically. Both infants had typical clinical features characterized by hypertrophic cardiomyopathy, bilateral cataracts, myopathy, and lactic acidosis, and heart failure was the most severe manifestation. Genetic testing of a boy revealed a homozygous pathogenic variant for Sengers syndrome in AGK (c.1131+2T>C) which was classified as likely pathogenic according to the ACMG guideline; besides, his skeletal muscle biopsy and transmission electron microscope presented obvious abnormity. One girl had compound heterozygous (c.409C>T and c.390G>A) variants of AGK gene that was identified in the proband and further Sanger sequencing indicated that the parents carried a single heterozygous mutation each. After the administration of “cocktail” therapy including coenzyme Q10, carnitine, and vitamin B complex, as well as ACEI, heart failure and myopathy of the boy were significantly improved and the condition was stable after 1-year follow-up, while the cardiomyopathy of the girl is not progressive but the plasma lactate acid increased significantly. We present the first report of two infants with Sengers syndrome diagnosed via exome sequencing in China.

Acylglycerol kinase promotes tumour growth and metastasis via activating the PI3K/AKT/GSK3β signalling pathway in renal cell carcinoma

Background Clinically, the median survival in patients with metastatic renal cell carcinoma (RCC) was only 6–12 months and a 5-year survival rate of less than 20%. Therefore, an in-depth study of the molecular mechanisms involved in RCC is of great significance for improving the survival of patients with advanced RCC. Acylglycerol kinase (AGK) is a newly discovered lipid kinase that has been reported to be a potent oncogene that may be involved in the regulation of malignant progression in a variety of tumours. However, the expression and biological characteristics of the AGK gene in RCC remain unclear. Methods AGK expression was quantified by quantitative real-time PCR, Western blotting and immunohistochemistry in RCC cell lines and paired patient tissues. Kaplan-Meier method and Cox proportional hazards models were used to evaluate the prognostic value of AGK in human RCC tissue samples. Chi-squared test was performed to analyse the correlation between AGK expression and the clinicopathological features. Stable overexpression and knockdown of AGK in RCC cells was constructed with lentivirus. The oncogenic effects of AGK in human RCC progression were investigated using assays of colony formation, anchorage-independent growth, EdU assay, cell cycle analysis, wound-healing, trans-well analysis and xenograft tumour model. GSEA and KEGG analysis were conducted to detect the potential pathway of AGK involved in RCC. These results were further confirmed using the luciferase reporter assays, immunofluorescence and in vivo experiments. Results AGK expression is significantly elevated in RCC and closely related to the malignant development and poor prognosis in RCC patients. By in vitro and in vivo experiments, AGK was shown to enhance the proliferation of RCC cells by promoting the transition from the G1 phase to the S phase in the cell cycle and to enhance the migration and invasion by promoting epithelial-mesenchymal transition. By activating the PI3K/AKT/GSK3β signalling pathway in RCC, AGK can increase nuclear accumulation of β-catenin, which further upregulated TCF/LEF transcription factor activity. Conclusions AGK promotes the progression of RCC via activating the PI3K/AKT/GSK3β signalling pathway and might be a potential target for the further research of RCC.