Mesopolysaccharides: The extracellular surface layer of visceral organs

Abstract

The mesothelium is a dynamic and specialized tissue layer that covers the somatic cavities (pleural, peritoneal, and pericardial) as well as the surface of the visceral organs such as the lung, heart, liver, bowel and tunica vaginalis testis. The potential therapeutic manipulation of visceral organs has been complicated by the carbohydrate surface layer-here, called the mesopolysaccharide (MPS)-that coats the outer layer of the mesothelium. The traditional understanding of MPS structure has relied upon fixation techniques known to degrade carbohydrates. The recent development of carbohydrate-preserving fixation for high resolution imaging techniques has provided an opportunity to reexamine the structure of both the MPS and the visceral mesothelium. In this report, we used high pressure freezing (HPF) as well as serial section transmission electron microscopy to redefine the structure of the MPS expressed on the murine lung, heart and liver surface. Tissue preserved by HPF and examined by transmission electron microscopy demonstrated a pleural MPS layer 13.01±1.1 um deep-a 100-fold increase in depth compared to previously reported data obtained with conventional fixation techniques. At the base of the MPS were microvilli 1.1±0.35 um long and 42±5 nm in diameter. Morphological evidence suggested that the MPS was anchored to the mesothelium by microvilli. In addition, membrane pits 97±17 nm in diameter were observed in the apical mesothelial membrane. The spatial proximity and surface density (29±4.5%) of the pits suggested an active process linked to the structural maintenance of the MPS. The striking magnitude and complex structure of the MPS indicates that it is an important consideration in studies of the visceral mesothelium.

Biomaterial-Assisted Anastomotic Healing: Serosal Adhesion of Pectin Films

“…The serosal surface of the bowel wall is covered with a serosal MPS. We have recently demonstrated that the MPS is 1000-times thicker than previously assumed—over 10 μm in thickness [ 24 ]. Moreover, high resolution imaging indicates that the serosal MPS demonstrates a branched-chain structure that mirrors the chain structure of pectin.…”

“…The samples were stained and processed as previously described using ruthenium red [ 24 ]. Briefly, samples were stained with ruthenium red (Sigma-Aldrich, Steinheim, Germany) while in 1% glutaraldehyde, then further processed with the rOTO protocol before embedding in Epon (Serva, Heidelberg, Germany).…”

“…The MPS is 100 to 1000-fold thicker than previously demonstrated. More than 10 μm thick, the MPS represents a substantial physical barrier [ 24 ]. Most likely an adaptation to facilitate unencumbered peristaltic movements within the abdominal cavity, the serosal MPS is non-adhesive and slippery.…”

Functional Adhesion of Pectin Biopolymers to the Lung Visceral Pleura

“…A variety of surgical techniques, including pleural flaps [ 40 ] and pleural tents [ 6 ], have been designed to facilitate the healing of pleural injures. Due to the structural biosimilarity of pectin and the pleural glycocalyx [ 41 ], we speculate that pectin may have a similar function in facilitating visceral pleural repair.…”

Immuno-Electron and Confocal Laser Scanning Microscopy of the Glycocalyx

“…It was shown that HPF immobilizes cellular structures in their near-native form within milliseconds and that subsequent dehydration and contrasting by FS allows for the preservation of ultrastructure and antigenicity due to a gradual temperature rise that successively replaces amorphous ice with organic solvents [ 10 , 22 ]. HPF/FS has recently been successfully applied to visualize the interaction of magnetic nanoparticles with the GCX of THP-1 cells during initial contact [ 9 ] and the extracellular surface layer of visceral organs [ 23 ].…”