Myosin in hepatocytes is essential for bile canalicular contraction

Alteration of liver enzymes is a feature of the MYH9-related disease syndrome

Background

MYH9-related disease (MYH9-RD) is a rare autosomal dominant genetic syndrome characterized by congenital thrombocytopenia associated with the risk of developing progressive nephropathy, sensorineural deafness, and presenile cataract. During the collection of a large case-series of patients with MYH9-RD we noticed several cases with unexplained elevation of liver enzymes. Our aim was to evaluate if the alteration of liver tests is a feature of the MYH9-RD and to define its clinical significance.

Methods and Findings

Data concerning liver tests, prospectively recorded in the Italian Registry for MYH9-RD, were collected and compared with those of three control populations: patients with autoimmune thrombocytopenia, patients with inherited thrombocytopenias other than MYH9-RD, and the participants to a large epidemiologic survey in an Italian geographic isolate. Thirty-eight of 75 evaluable MYH9-RD patients (50.7%) showed an elevation of ALT and/or AST, and 17 of 63 (27.0%) an increase of GGT. The increases ranged from 1.9±0.7 to 2.7±1.6 fold the upper normal limit. The prevalence of liver test alterations was significantly higher in MYH9-RD patients than in each of the control populations, with odds ratios ranging from 8.2 (95% CIs 2.2–44.8) to 24.7 (14.8–40.8). Clinical follow-up and more detailed liver studies of a subset of patients, including ultrasound liver scan, liver elastography and liver biopsy in one case, did not show any significant structural damage or evolution towards liver insufficiency.

Conclusions

Elevation of liver enzymes is a frequent and previously unrecognized feature of the MYH9-RD syndrome; however, this defect does not appear to have poor prognostic value.

Coordinated Movement of Bile Canalicular Networks Reconstructed by Rat Small Hepatocytes

Hepatocytes in vivo have a potential for liver regeneration, but it has been very difficult to reconstruct hepatic organoids in vitro. Recent studies have shown that small hepatocytes (SHs) can reconstruct hepatic organoids including functional bile canaliculi (BC). In the present study we analyzed the movement of BC formed in the hepatic organoids, focusing on the coordination of contraction and dilation among cells and the mechanism producing the coordination. Hepatic cells, including SHs, were isolated from an adult rat liver and cultured. Time-lapse images of BC movements were taken and analyzed in cells treated with or without cytochalasin B (CB). Time-lapse images revealed that all BC, regardless of region contracted in a coordinated manner. Actin filaments were observed along the BC even after the BC networks treated with CB dilated markedly. Microinjection of dye was also carried out to investigate the flow thorough BC. Secreted fluorescein from the injected cell flowed along BC, and gap junctional protein connexin 32 was expressed along BC networks, suggesting cell-to-cell communication. Thus, groups of hepatocytes in the hepatic organoids act in a coordinated manner through intercellular communication.

Development and maintenance of bile canaliculi in vitro and in vivo

The apical surfaces of hepatocytes are specialized to form the boundaries of the bile canaliculi. The canaliculi function to secrete and concentrate components of the bile and to transport the bile out of the interior of the hepatic parenchymal tissue to the epithelium-lined bile ducts. Failure of the canaliculi to form and function properly can lead to biliary stasis or release of bile components into the bloodstream, both potentially life-threatening situations. Experimental analysis of canaliculus development and function has been undertaken in a number of experimental systems, ranging in complexity from intact animals to isolated hepatocyte cell cultures. These approaches each have inherent advantages and disadvantages for studying the various aspects of canaliculus development and function. This article summarizes what is known about how the functional components of the canaliculus develop and the directions that current experimental approaches are leading in analyzing this process. Studies of model epithelial systems have begun to define how interactions between components of the cytoskeleton and plasma membrane regulate the structure of polarized plasma membranes. These results are also discussed in terms of the bile canaliculus.

The role of the cytoskeleton in migration and proliferation of a cultured human gastric cancer cell line using a new metastasis model

Using an in vitro model for investigating the mechanism of migration and proliferation of a cultured human gastric cancer cell line which we established recently, we studied the suppressive effect of inhibitors of the cytoskeleton proteins, actin and myosin, on the migration and proliferation of cancer cells. These inhibitors suppressed the capacity of cancer cells to migrate and proliferate dose-dependently. Thus the integrity of the cytoskeletal system may play an important role in the mechanism of metastasis of gastric cancer cells.

Ethanol retards gastric epithelial restoration in monolayer cultures

The purpose of this study was to clarify the effect of ethanol on confluent monolayer gastric epithelial cells that had a round cell-free area in the center of the culture dish. Restoration of such "wounding" was evaluated quantitatively every 12 hr using a computer image analyzer with and without ethanol. Without ethanol, restoration was achieved within 48 hr. Exposure to ethanol retarded cellular restoration significantly. Staining for actin and myosin in the control group revealed the presence of lamellipodia and stress fibers. However, in the ethanol group narrowed lamellipodia and few stress fibers were observed. In conclusion, ethanol retarded the migration and proliferation of cultured gastric mucosal cells after in vitro wounding, possibly by damaging the cytoskeletal system.

Monoclonal antibodies to rabbit hepatocyte myosin that cross-react with human liver myosin

We prepared polyclonal and monoclonal antibodies against myosin purified from rabbit hepatocytes. Immunoblotting analyses revealed that the polyclonal antibody and four (HM1, HM2, HM3 and HM4) of five monoclonal antibodies reacted with myosin heavy chain. Chymotryptic cleavage of myosin yielded a 130 kDa fragment comprising the tail portion of the myosin heavy chain and a 67 kDa fragment comprising the ATP-binding active site of the myosin head. All active antibodies reacted with epitopes localized in the 130 kDa fragment. Monoclonal antibodies HM3 and HM4 and the polyclonal antibody reacted strongly with myosin heavy chains from a human liver homogenate prepared from a surgically resected liver specimen. Immunocytochemical analyses showed that myosin is localized along the plasma membrane as well as around the bile canaliculi in both rabbit and human hepatocytes. Immunocytochemical analyses on liver blocks obtained from those patients who suffered various types of diseases accompanying cholestasis clearly indicated a marked increase in pericanalicular myosin. This altered myosin localization is analogous to that observed in phalloidin-treated liver. Thus, myosin localization, determined using these antibodies, can provide a valid morphological basis for diagnosing the pathological state of the patient liver.

Role of actin and calmodulin in migration and proliferation of rabbit gastric mucosal cells in culture

The aim of this study was to develop a new cellular restoration model using primary cultured rabbit gastric mucosal cells, and to evaluate the role of cytoskeleton and calmodulin in this process. Confluent monolayer mucosal cell sheets consisting mainly of mucous cells were wounded, and a rotating silicon tip was used to make cell-free areas of constant size. The process of restoration was monitored, and the cell-free area was measured and analysed quantitatively. Artificial wounds recovered in 36 h in controls; however, mucosal cell repair was inhibited by treatment with the actin inhibitor, cytochalasin B, and the calmodulin inhibitor, W-7. In the process of restoration, bromodeoxyuridine (BrdU)-positive cells appeared around the wound 24 h after injury and then disappeared after the complete repair. Because BrdU-positive cells were never detected within 24 h after wounding, initial recovery of the wound occurred only by cell migration. Both the migration and the proliferation stage are seen with this model. This culture model is suitable for the analysis of gastric mucosal restoration. Present data are consistent with the hypothesis that the integrity of the cytoskeletal system is important for restoration after damage of the gastric mucosa.