The intricate role of annexin A2 in kidney: a comprehensive review

Annexin A2 (Anxa2) is a calcium (Ca2+)-regulated phospholipid binding protein composed of a variable N-terminus and a conserved core domain. This protein has been widely found in many tissues and fluids, including tubule cells, glomerular epithelial cells, renal vessels, and urine. In acute kidney injury, the expression level of this protein is markedly elevated in response to acute stress. Moreover, Anxa2 is a novel biomarker and potential therapeutic target with prognostic value in chronic kidney disease. In addition, Anxa2 is associated not only with clear-cell renal cell carcinoma differentiation but also the formation of calcium-related nephrolithiasis. In this review, we discuss the characteristics and functions of Anxa2 and focus on recent reports on the role of Anxa2 in the kidney, which may be useful for future research.

Antiphospholipid Antibodies and Lipids in Hematological Malignancies

One of the main groups of lipids is phospholipids, which are mainly involved in forming cell membranes. Neoplastic processes such as cell replication have increased lipid synthesis, making tumor cells dependent on this synthesis to maintain their requirements. Antiphospholipid antibodies attack phospholipids in the cell membranes. Three main types of antiphospholipid antibodies are recognized: anti-β2 glycoprotein I (anti-β2GP-I), anticardiolipin (aCL), and lupus anticoagulant (LA). These types of antibodies have been proven to be present in hematological neoplasms, particularly in LH and NHL. This review on antiphospholipid antibodies in hematological neoplasms describes their clinical relationship as future implications at the prognostic level for survival and even treatment.

The Ca2+- and phospholipid-binding protein Annexin A2 is able to increase and decrease plasma membrane order

Annexin A2 (AnxA2) is a calcium- and phospholipid-binding protein that plays roles in cellular processes involving membrane and cytoskeleton dynamics and is able to associate to several partner proteins. However, the principal molecular partners of AnxA2 are negatively charged phospholipids such as phosphatidylserine and phosphatidyl-inositol-(4,5)-phosphate. Herein we have studied different aspects of membrane lipid rearrangements induced by AnxA2 membrane binding. X-ray diffraction data revealed that AnxA2 has the property to stabilize lamellar structures and to block the formation of highly curved lipid phases (inverted hexagonal phase, H_II). By using pyrene-labelled cholesterol and the environmental probe di-4-ANEPPDHQ, we observed that in model membranes, AnxA2 is able to modify both, cholesterol distribution and lipid compaction. In epithelial cells, we observed that AnxA2 localizes to membranes of different lipid order. The protein binding to membranes resulted in both, increases and/or decreases in membrane order depending on the cellular membrane regions. Overall, AnxA2 showed the capacity to modulate plasma membrane properties by inducing lipid redistribution that may lead to an increase in order or disorder of the membranes.

5α-Epoxyalantolactone Inhibits Metastasis of Triple-Negative Breast Cancer Cells by Covalently Binding a Conserved Cysteine of Annexin A2

Triple-negative breast cancer (TNBC) has been considered the most aggressive and mortal breast cancer. Thus far, it remains an important challenge to develop TNBC targeted therapy. As revealed from numerous recent studies, ANXA2 may be a potential target to treat TNBC. In the present study, a natural product 5α-epoxyalantolactone (5α-EAL) was discovered as an anti-breast cancer stem cells (BCSCs) lead compound. Furthermore, 5α-EAL was found to be able to notably suppress the function of ANXA2 by covalently targeting cysteine 9 (Cys9) of ANXA2. To the best of our knowledge, 5α-EAL was recognized as the first small molecule functional inhibitor of ANXA2. It could significantly inhibit the formation of the heterotetrameric complex of ANXA2 and S100A10, which is capable of transporting E-cadherin (E-Ca) to the membrane. The above findings may be used as a possible strategy to develop novel anti-TNBC therapies targeting ANXA2.

Deficiency of Mitochondrial Glycerol 3-Phosphate Dehydrogenase Exacerbates Podocyte Injury and the Progression of Diabetic Kidney Disease

Mitochondrial function is essential for bioenergetics, metabolism, and signaling and is compromised in diseases such as proteinuric kidney diseases, contributing to the global burden of kidney failure, cardiovascular morbidity, and death. The key cell type that prevents proteinuria is the terminally differentiated glomerular podocyte. In this study, we characterized the importance of mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH), located on the inner mitochondrial membrane, in regulating podocyte function and glomerular disease. Specifically, podocyte-dominated mGPDH expression was downregulated in the glomeruli of patients and mice with diabetic kidney disease and adriamycin nephropathy. Podocyte-specific depletion of mGPDH in mice exacerbated diabetes- or adriamycin-induced proteinuria, podocyte injury, and glomerular pathology. RNA sequencing revealed that mGPDH regulated the receptor for the advanced glycation end product (RAGE) signaling pathway, and inhibition of RAGE or its ligand, S100A10, protected against the impaired mitochondrial bioenergetics and increased reactive oxygen species generation caused by mGPDH knockdown in cultured podocytes. Moreover, RAGE deletion in podocytes attenuated nephropathy progression in mGPDH-deficient diabetic mice. Rescue of podocyte mGPDH expression in mice with established glomerular injury significantly improved their renal function. In summary, our study proposes that activation of mGPDH induces mitochondrial biogenesis and reinforces mitochondrial function, which may provide a potential therapeutic target for preventing podocyte injury and proteinuria in diabetic kidney disease.

The endometrial proteomic profile around the time of embryo implantation†

Embryo implantation is an intricate process which requires competent embryo and receptive endometrium. The failure of endometrium to achieve receptivity is a recognized cause of infertility. However, due to multiplicity of events involved, the molecular mechanisms governing endometrial receptivity are still not fully understood. Traditional one-by-one approaches, including western blotting and histochemistry, are insufficient to examine the extensive changes of endometrial proteome. Although genomics and transcriptomics studies have identified several significant genes, the underlying mechanism remains to be uncovered owing to post-transcriptional and post-translational modifications. Proteomic technologies are high throughput in protein identification, and they are now intensively used to identify diagnostic and prognostic markers in the field of reproductive medicine. There is a series of studies analyzing endometrial proteomic profile, which has provided a mechanistic insight into implantation failure. These published studies mainly focused on the difference between pre-receptive and receptive stages of endometrium, as well as on the alternation of endometrial proteomics in women with reproductive failure. Here, we review recent data from proteomic analyses regarding endometrium around the time of embryo implantation and propose possible future research directions.