Comparision of Exosome Proteins

Exosome are considered as one of the key biomarker for different disease at present time. Exosome is combination of protein, lipids, RNA and metabolites. Exosome associated protein is primarily been used for detection of disease. Research works are reported on analysis of different Exosome associated protein and its use as biomarker especially for urine, heart and cancer related disease. In present review report a brief work on Exosome so far done is reported. Composition of Exosome associate protein, its biological process and method of detections are widely discussed.

Introduction

Exosome consists of protein, lipids, RNA and metabolites. Exosomes were first discovered in reticulocyte (immature blood cell) by Stahel et.al. in 1987. When reticulocyte becomes mature i.e. erythrocyte, exosomes start participating in selective removal of good number of plasma membrane protein [1]. During recycling of plasma membrane, exosome behave like a intraluminal vesicles of multivesicular (MVB). It has been reported [2] that exosome are released by many cell type and is supposed to act as medium for detaching many obsolete protein. It has been recently reported that there is a range of exosomal functions, it involve in intercellular transfer of membrane receptors and RNA, induction of immunity, antigen presentation, modulation of bone mineralization,[3] and antiapoptotic responses[3-7].

Evidence of urine exosome was reported [8] As per report, exosomes shows consistency with a renal tubular epithelial origin. This report further establishes relation for renal tubular epithelial cells contain MVBs at the apical surface. Urine exosomes have apical membrane proteins from every cell type beside the nephron.it has also been established by different workers that the array of functions credited to exosomes in other tissues, it has open a new area of research on the functional significance of urinary exosomes. It also proposed that there seems interaction of exosome vehicle with primary cilia of renal epithelial cells. It has also been found by Street et.al [9 ]that in vitro uptake of exosomes by a renal cortical collecting duct cell line, leading to speculation that exosomes may provide intrarenal proximal-to-distal transapical renal tubular epithelial signaling through RNA transfer. Present time most of the report on Exosome are coming foussed to the application in the direction of biomarker discovery[10 ].

 Composition of Exosome

Exosomes are formed from EV (Exosomal Vesicles) process of formation involves endosomal route. Exosome have diameter in the range varying between 30–150 nm.[11]. Specifically, exosomal vesicles form by inner budding of the limiting membrane of early endosomes, which mature into ultivesicular bodies (MVBs) through the development [12]. Early endosomes, which create from inner up-and-coming of the cell’s plasma membrane, and MVBs are mixed up in the endocytic and tracking functions of the cell’s material [13]. Specifically, they are occupied in protein categorization, recycling, storage, transport, and release [13]. MVBs are ultimately moreover send to the lysosome to be tainted all along with all of its components or fused with the cell’s plasma membrane to release its content, including exosomes, into the extracellular space [14]. The factors that decide the fortune of a specific MVB are not fine understood [15]. Though, many researches have been done to reveal that the fortune of a meticulous MVB depends on the level of cholesterol in the MVB. Particularly, a cholesterol affluent vesicle was concealed while a morphologically identical vesicle that lacked cholesterol was sent to the lysosome for degradation [15]. The guideline of MVB and exosome arrangement and liberate is from side to side the endosomal categorization complexes required for transport (ESCRT) pathway [14-15]. While the correct basis is still not entirely understood, it appears the configuration of MVBs can be motivated by growth factors and the cell adjusts its exosome creation according to its needs [14-15].

The biogenesis of exosomes can be helpful to recognize the proteome of the vesicles. Exosomal creation and MVB haulage are synchronized by ESCRT proteins, these proteins and its accomplice proteins are likely to be originate in exosomes despite of the kind of cell as of they start off [16]. As a result, these sets of proteins are habitually termed “exosomal marker proteins.” Researchers hasreported about an another method, which is an ESCRT free method, by which a number of cells liberate exosomes into the extracellular space [16]. In this particular method, exosome libration is considered to depend on sphingomyelinase enzyme instead of ESCRT, because cells exhausted of the ESCRT mechanism still created CD63 positive exosomes [16-17]. Exosome CD63, beside with CD9 and CD81, are proteins in the tetraspanin family. These proteins, and supplementary proteins connected with the plasma membrane, are normally found in exosomes and are frequently enriched in the vesicles compared to the cell lysate [17].

At first, it was assumed that tetraspanin proteins were explicit markers of exosomes, Though, these proteins have since been recognized in MVs and apoptotic bodies [18]. Exosomes is expected to be enriched in glycoproteins compared to the secreting cells, but, MVs are known to have proteins through higher levels of posttranslational modifications (PTMs), such as glycosylation and phosphorylation, compared to exosomes, which is a likely mode to differentiate the vesicles based on content rather than size [12,18-19]. As a final point, a current study [19] reported interorganelle tracking between mitochondria and the endolysosomal system, which clearly proves wrong the unproven code of belief that proteins particularly associated with organelles such as mitochondria and the nucleus are not probable to be observed in the exosomal vesicles. Proteins linked with the Golgi apparatus and endoplasmic reticulum, still, are supposed to be there at low levels because early endosomes can take action jointly with these organelles. On the other hand, such proteins are characteristically still considered to be non-exosomal marker proteins because they are at lower levels in the exosomes compared to the lysate.