Western blot results confirmed expression of exosomal specific markers CD63 and CD81
in these exosomes (Figure 2(c)).
They also highlighted the trophic proteins, including surface receptors (e.g., PDG-FRB, EGFR, and PLAUR), signaling molecules (e.g., MAPK1, CDC42, RRAS/NRAS, and VAV2), and cell adhesion (e.g., EZR, FN1, IQGAP1, CD47, integrins, and LGALS1/ LGALS3) and MSC-associated proteins (e.g., CD9, CD63, CD81
, CD109, CD151, CD248, and CD276).
The EV Array, used for phenotyping of EVs, is optimized for detection of small EVs with a size below 150 nm that present CD9, CD63, and/or CD81
, such as exosomes and exosome-like vesicles.
Exosomes are classified by tetraspanins CD9, CD63, and CD81
and the proteins Alix and TSG101 involved in MVB biogenesis.
HVR2 is proximal to the CD81
binding regions of E2, while the intergenotypic variable region (IgVR) lies closer to the transmembrane domain of E2 .
The protein composition is diverse and depends on the cellular type and the physiological context; nevertheless, as they originate in the endocytic pathway, the most common proteins independent of the cell type of origin are related to vesicular transport and fusion (Rab GTPasas, SNAREs, annexins, and flotillin), different integrins and tetraspanins (CD63, CD9, CD81
, and CD82), and heat shock proteins (Hsc/Hsp 70 and 90) and proteins implicated in the biogenesis of MVB (Alix and TSG 101) .
Moreover, MSC-EVs also express the two characteristic markers of EVs, CD81
and CD63 [39, 40].
Regardless of origin, several common proteins are found in exosomes, including chaperones, cytoskeletal proteins, and tetraspanins such as CD9, CD63, and CD81
MSC exosomes, like exosomes in general, carry exosome-associated markers such as Alix, tetraspanins (CD9, CD63, and CD81
), and heat-shock proteins including Hsp60, Hsp70, and Hsp90.
[MV.sub.contr] contained complement factors (C3, C4A, and C5) and lipid binding proteins (i.e., apolipoproteins), whereas the [MV.sub.stim] contained tetraspanins (CD9, CD63, and CD81
) and more complete proteasome complex accompanied with MHCI.
Moreover, other putative markers can be used to isolate SG stem/progenitor cells including KRT5 (Cytokeratin 5), CD49f, CD29 (Itga1), CD133 (Prom1), Sca1, CD44, CD34, CD90 (Thy1), CD105, CD9, and CD81
, but only few populations were proven to actively restore damaged glands [11, 42-45].