Effects of Advanced Glycation End Products on Ezrin-Dependent Functions in LLC-PK1 Proximal Tubule Cells

Radixin: Roles in the Nervous System and Beyond

BACKGROUND

Radixin is an ERM family protein that includes radixin, moesin, and ezrin. The importance of ERM family proteins has been attracting more attention, and studies on the roles of ERM in biological function and the pathogenesis of some diseases are accumulating. In particular, we have found that radixin is the most dramatically changed ERM protein in elevated glucose-treated Schwann cells.

METHOD

We systemically review the literature on ERM, radixin in focus, and update the roles of radixin in regulating cell morphology, interaction, and cell signaling pathways. The potential of radixin as a therapeutic target in neurodegenerative diseases and cancer was also discussed.

RESULTS

Radixin research has focused on its cell functions, activation, and pathogenic roles in some diseases. Radixin and other ERM proteins maintain cell shape, growth, and motility. In the nervous system, radixin has been shown to prevent neurodegeneration and axonal growth. The activation of radixin is through phosphorylation of its conserved threonine residues. Radixin functions in cell signaling pathways by binding to membrane proteins and relaying the cell signals into the cells. Deficiency of radixin has been involved in the pathogenic process of diseases in the central nervous system and diabetic peripheral nerve injury. Moreover, radixin also plays a role in cell growth and drug resistance in multiple cancers. The trials of therapeutic potential through radixin modulation have been accumulating. However, the exact mechanisms underlying the roles of radixin are far from clarification.

CONCLUSIONS

Radixin plays various roles in cells and is involved in developing neurodegenerative diseases and many types of cancers. Therefore, radixin may be considered a potential target for developing therapeutic strategies for its related diseases. Further elucidation of the function and the cell signaling pathways that are linked to radixin may open the avenue to finding novel therapeutic strategies for diseases in the nervous system and other body systems.

Role of moesin in renal fibrosis

Background

Renal fibrosis is the final common pathway of chronic kidney disease (CKD). Moesin is a member of Ezrin/Radixin/Moesin (ERM) protein family but its role in renal fibrosis is not clear.

Method

Human proximal tubular cells (HK-2) were stimulated with or without TGF-β1. Moesin and downstream target genes were examined by real-time PCR and western blot. Phosphorylation of moesin and related signaling pathway was investigated as well. Rat model of unilateral ureteral obstruction (UUO) was established and renal moesin was examined by immunohistochemistry. Moesin in HK-2 cells were knocked down by siRNA and change of downstream genes in transfected HK-2 cells was studied. All animal experiments were reviewed and approved by the Ethics Committee for animal care of Ruijin Hospital.

Result

HK-2 cells stimulated with TGF-β1 showed up-regulated level of α-SMA and down-regulated level of E-Cadherin as well as elevated mRNA and protein level of moesin. In rat model of UUO, renal moesin expression increased in accordance with severity of tubulointerestital fibrosis in the kidneys with ureteral ligation while the contralateral kidneys were normal. Further study showed that TGF-β1 could induce phosphorylation of moesin which depended on Erk signaling pathway and Erk inhibitor PD98059 could block moesin phosphorylation. Effects of TGF-β1 on moesin phosphorylation was prior to its activation to total moesin. RNA silencing studies showed that knocking down of moesin could attenuate decrease of E-Cadherin induced by TGF-β1.

Conclusion

We find that moesin might be involved in renal fibrosis and its effects could be related to interacting with E-Cadherin.

Actin binding proteins and spermiogenesis: Some unexpected findings

Drebrin E, an actin-binding protein lacking intrinsic activity in the regulation of actin dynamics (e.g., polymerization, capping, nucleation, branching, cross-linking, bundling and severing), is known to recruit actin regulatory proteins to a specific cellular site. Herein, we critically evaluate recent findings in the field which illustrate that drebrin E works together with two other actin-binding proteins, namely Arp3 (actin-related protein 3, a component of the Arp2/3 complex that simultaneously controls actin nucleation for polymerization and branching of actin filaments) and Eps8 (epidermal growth factor receptor pathway substrate 8 that controls capping of the barbed ends of actin filaments, as well as actin filament bundling) to regulate the homeostasis of F-actin filament bundles at the ectoplasmic specialization (ES), a testis-specific atypical adherens junction (AJ) in the seminiferous epithelium. This is mediated by the strict temporal and spatial expression of these three actin-binding proteins at the apical and basal ES at the Sertoli cell-spermatid (step 8-19) and Sertoli-Sertoli cell interface, respectively, during the seminiferous epithelial cycle of spermatogenesis. In this Commentary, we put forth a possible model by which drebrin E may be acting as a platform upon which proteins (e.g., Arp3) that are needed to alter the conformation of actin filament bundles at the ES can be recruited to the site, thus facilitating changes in cell shape and cell position in the epithelium during spermiogenesis and spermiation. In short, drebrin E may be acting as a "logistic" distribution center to manage different regulatory proteins at the apical ES, thereby regulating the dynamics of actin filament bundles and modulating the plasticity of the apical ES. This would allow adhesion to be altered continuously throughout the epithelial cycle to accommodate spermatid movement in the seminiferous epithelium during spermiogenesis and spermiation. We also describe a hypothetical model, upon which functional studies can be designed in the future.

Protective effects of ezrin on cold storage preservation injury in the pig kidney proximal tubular epithelial cell line (LLC-PK1)

BACKGROUND

Renal damage caused by cold preservation and warm reperfusion has been well documented and involves tissue edema, cell swelling, ATP depletion, calcium toxicity, and oxidative stress. However, more common proximal mechanisms have not been identified, which may limit the development of effective clinical treatment strategies. Previous work indicates that many cytoskeletal structures are affected by cold preservation and reperfusion, including membrane-rich ezrin-associated complexes. The aim of this study was to investigate whether the sublamellar cytoskeletal protein ezrin is causally involved in cold preservation injury in renal tubule epithelial cells.

METHODS

We created a stably transfected cell line (LLC-EZ) using the pig kidney proximal tubular epithelial cell line (LLC-PK1), which constitutively overexpresses wild-type ezrin. These cells were cold stored in University of Wisconsin Solution and reperfused in vitro to model renal tubule preservation injury, which was assessed by biochemical, metabolic, functional, and structural endpoints.

RESULTS

Overexpression of ezrin increased cell viability (lactate dehydrogenase release), mitochondrial activity (ATP synthesis, dehydrogenase activity, and inner mitochondrial membrane potential), and protected the structure of cell membrane microvilli and mitochondria after cold storage preservation injury. Reperfusion-induced apoptosis was also significantly reduced in LLC-EZ cells overexpressing ezrin.

CONCLUSIONS

Enhanced ezrin expression protects tubule epithelial cells from cold storage preservation injury, possibly by membrane or mitochondrial mechanisms.

Induction of reactive oxygen species and cell survival in the presence of advanced glycation end products and similar structures

Advanced glycation end products (AGEs) that arise from the reaction of sugars with protein side chains and the terminal amino group are supposed to be involved in the pathogenesis of several diseases and therefore the effects of AGEs on cells are the objective of numerous investigations. The effects of AGEs on cells are commonly assumed to be transduced via the receptor for AGEs (RAGE) but there are also other receptors known to interact with AGEs and they are likely to be involved in signal transduction. The primary cellular effect of AGEs on cultured cells was found to be the formation of reactive oxygen species (ROS). For the present study one murine and three human cell lines were used. The effects of a set of different highly modified AGEs and AGE-like compounds derived from the incubation of different modifiers with BSA were tested for their effects on these cells. Almost all AGEs tested induced the production of reactive oxygen species (ROS) in the different cell lines although the intensity of the detected signals varied considerably between the cell lines and are strongly dependent on the AGE used for cell activation. The most highly modified BSA-species were shown to inhibit cell growth in all cell lines, whereas a moderately modified glucose derived BSA-AGE and BSA-GA(red) did not show any inhibitory effect on cell growth even when a high ROS formation was detected.