Formation of actin filament networks in cultured rat hepatocytes treated with DMSO and glucagon

Cardiomyocyte mechanodynamics under conditions of actin remodelling

The mechanical performance of cardiomyocytes (CMs) is an important indicator of their maturation state and of primary importance for the development of therapies based on cardiac stem cells. As the mechanical analysis of adherent cells at high-throughput remains challenging, we explore the applicability of real-time deformability cytometry (RT-DC) to probe cardiomyocytes in suspension. RT-DC is a microfluidic technology allowing for real-time mechanical analysis of thousands of cells with a throughput exceeding 1000 cells per second. For CMs derived from human-induced pluripotent stem cells, we determined a Young's modulus of 1.25 ± 0.08 kPa which is in close range to previous reports. Upon challenging the cytoskeleton with cytochalasin D (CytoD) to induce filamentous actin depolymerization, we distinguish three different regimes in cellular elasticity. Transitions are observed below 10 nM and above 103 nM and are characterized by a decrease in Young's modulus. These regimes can be linked to cytoskeletal and sarcomeric actin contributions by CM contractility measurements at varying CytoD concentrations, where we observe a significant reduction in pulse duration only above 103 nM while no change is found for compound exposure at lower concentrations. Comparing our results to mechanical cell measurements using atomic force microscopy, we demonstrate for the first time to our knowledge, the feasibility of using a microfluidic technique to measure mechanical properties of large samples of adherent cells while linking our results to the composition of the cytoskeletal network. This article is part of a discussion meeting issue 'Single cell ecology'.

Effects of medium composition on the morphology and function of rat hepatocytes cultured as spheroids and monolayers

Primary hepatocytes cultured as monolayers or as spheroids were studied to compare the effects of four different culture media (Williams' E, Chee's, Sigma Hepatocyte, and HepatoZYME medium). Rat hepatocytes were cultured as conventional monolayers for 3 d or as spheroids for 2 wk. For spheroid formation a method was emplOyed that combined the use of a nonadherent substratum with rotation of cultures. Hepatocyte integrity and morphology were assessed by light and electron microscopy and by reduced glutathione content. Hepatocyte function was measured by albumin secretion and 7-ethoxycoumarin metabolism. Chee's medium was found to be optimal for maintenance of hepatocyte viability and function in monolayers, but it failed to support spheroid formation. For spheroid formation and for the maintenance of spheroid morphology and function, Sigma HM was found to be optimal. These results demonstrate that the medium requirements of hepatocytes differ markedly depending on the culture model employed. Spheroid culture allowed better preservation of morphology and function of hepatocytes compared with conventional monolayer culture. Hepatocytes in spheroids formed bile canaliculi. and expressed an actin distribution resembling that found in hepatocytes in vivo. Albumin secretion was maintained at the same level as that found during the first d in primary culture, and 7-ethoxycoumarin metabolism was maintained over 2 wk in culture at approximately 30% of the levels found in freshly isolated hepatocytes. The improved morphology and function of hepatocyte cultures as spheroids may provide a more appropriate in vitro model for certain applications where the maintenance of liver-specific functions in long-term culture is crucial.

Effects of medium composition on the morphology and function of rat hepatocytes cultured as spheroids and monolayers

Primary hepatocytes cultured as monolayers or as spheroids were studied to compare the effects of four different culture media (Williams' E, Chee's, Sigma Hepatocyte, and HepatoZYME medium). Rat hepatocytes were cultured as conventional monolayers for 3 d or as spheroids for 2 wk. For spheroid formation a method was emplOyed that combined the use of a nonadherent substratum with rotation of cultures. Hepatocyte integrity and morphology were assessed by light and electron microscopy and by reduced glutathione content. Hepatocyte function was measured by albumin secretion and 7-ethoxycoumarin metabolism. Chee's medium was found to be optimal for maintenance of hepatocyte viability and function in monolayers, but it failed to support spheroid formation. For spheroid formation and for the maintenance of spheroid morphology and function, Sigma HM was found to be optimal. These results demonstrate that the medium requirements of hepatocytes differ markedly depending on the culture model employed. Spheroid culture allowed better preservation of morphology and function of hepatocytes compared with conventional monolayer culture. Hepatocytes in spheroids formed bile canaliculi. and expressed an actin distribution resembling that found in hepatocytes in vivo. Albumin secretion was maintained at the same level as that found during the first d in primary culture, and 7-ethoxycoumarin metabolism was maintained over 2 wk in culture at approximately 30% of the levels found in freshly isolated hepatocytes. The improved morphology and function of hepatocyte cultures as spheroids may provide a more appropriate in vitro model for certain applications where the maintenance of liver-specific functions in long-term culture is crucial.

The heterogeneous response of the bivascularly perfused rat liver to adenosine

The heterogeneity of the liver parenchyma in relation to the metabolic response to adenosine was investigated using the bivascularly perfused rat liver in the anterograde and retrograde modes. Adenosine was infused into livers from fed rats according to four experimental protocols: (A) anterograde perfusion, adenosine via the portal vein; (B) anterograde perfusion, adenosine via the hepatic artery; (C) retrograde perfusion, adenosine via the hepatic vein; and (D) retrograde perfusion, adenosine via the hepatic artery. Due to the very pronounced concentration gradients generated by metabolic transformation, the infused adenosine attained maximal concentrations in different regions with each experimental protocol. The sinusoidal mean transit times (t(s)) were not changed by adenosine in anterograde perfusion, but were increased in retrograde perfusion. It was concluded that the vasoconstrictive elements are localized essentially in the presinusoidal region. Glucose release stimulation presented two kinetic components. The first one was rapid in both onset and decay with a peak around 30 sec; the second one developed more slowly (several minutes). The factors of the first kinetic component are possibly generated in the presinusoidal region or in the first periportal cells. The initial decrease in oxygen consumption seemed to be localized in the region just after the intrasinusoidal confluence of the ramifications of the portal vein and hepatic artery. Indomethacin decreased glucose release stimulation by adenosine in both anterograde and retrograde perfusion only when DMSO was the vehicle. The participation of eicosanoids in the generation of the effects of adenosine seems to be less important than hitherto believed.

Combined effects of H-7 and cytochalasin B on outflow facility in monkeys

The serine-threonine protein kinase inhibitor H-7 and the fungal metabolite cytochalasin B (CB) disrupt the actin microfilament network by different mechanisms, and increase outflow facility similarly in live monkeys. Their combined effect has therefore determined on total outflow facility in cynomolgus monkeys by 2-level constant pressure perfusion. (1) After unilateral anterior chamber (AC) bolus injection of H-7 [10 micrometers, 100 micrometers (subthreshold for increasing facility when given alone) or 500 micrometers (just-threshold)] followed by bilateral AC bolus injection of CB [2 micrograms (strong but submaximal for increasing facility when given alone)], no significant difference between eyes was observed. (2) After bilateral AC exchange with a subthreshold dose of H-7 (10 micrometers) followed by unilateral AC bolus injection of a subthreshold dose of CB (0.02, 0.05, 0.1 or 0.5 microgram), 10 micrometers H-7 plus 0.1 or 0.5 microgram CB increased facility by approximately 40 or 80% compared to 10 micrometers H-7 alone. (3) After bilateral AC exchange with a maximal dose of H-7 (300 micrometers), followed by unilateral AC bolus injection of a subthreshold dose of CB (0.1 or 0.5 microgram), 300 micrometers H-7 plus 0.5 microgram CB increased outflow facility by 47% compared to 300 micrometers H-7 alone. (4) After unilateral AC exchange with a maximal dose of H-7 (300 micrometers) followed by bilateral AC bolus injection of a near-maximal dose of CB (2 micrograms), 300 micrometers H-7 plus 2 micrograms CB increased the facility by 67% compared to 2 micrograms CB alone. The significant effect of combined subthreshold doses of H-7 and CB on outflow facility, the potentiation of the facility-increasing effect of a maximal H-7 dose by both subthreshold and near-maximal CB doses, and the known cytoskeletal effects of both compounds, may suggest that both increase facility by disrupting actin filaments in the trabecular meshwork.

Disruption of circumferential actin filament causes disappearance of occludin from the cell borders of rat hepatocytes in primary culture without distinct changes of tight junction strands

We investigated the relationship of actin filament organization to occludin and tight junction strands in primary cultured rat hepatocytes using an actin depolymerizing agent, mycalolide B. In control cultures, well-developed circumferential actin filaments and occludin immunoreactivity were observed on the most subapical plasma membrane of the cells, and tight junction strands formed well-developed networks in freeze-fracture replicas. In hepatocytes treated with 3 microM mycalolide B for 6 h, circumferential actin filaments and occludin immunoreactivity disappeared from the cell borders. However, there were no marked abnormalities of tight junction strands in freeze fracture replicas. Similar results were obtained from cells cultured in medium with 0.05 mM Ca2+ for 6 h. The close association of occludin with actin and the existence of intact tight junction strands that are virtually free of both occludin and actin suggest a physiological role of occludin, but not the other proteins forming the tight junction strands, in the linkage between actin cytoskeleton and tight junction.

The current status of primary hepatocyte culture

Recently, there have been significant advances toward the development of culture conditions that promote proliferation of primary rodent hepatocytes. There are two major methods for the multiplication of hepatocytes in vitro: one is the use of nicotinamide, the other is the use of a nutrient-rich medium. In the medium containing a high concentration of nicotinamide and a growth factor, primary hepatocytes can proliferate well. In this culture condition small mononucleate cells, which are named small hepatocytes, appear and form colonies. Small hepatocytes have a high potential to proliferate while maintaining hepatic characteristics, and can differentiate into mature ones. On the other hand, combining the nutrient-rich medium with 2% DMSO, the proliferated hepatocytes can recover the hepatic differentiated functions and maintain them for a long time. In this review I describe the culture conditions for the proliferation and differentiation of primary hepatocytes and discuss the small hepatocytes, especially their roles in liver growth.

Alteration of expression of liver-enriched transcription factors in the transition between growth and differentiation of primary cultured rat hepatocytes

In the present study, we showed the role of the liver-enriched transcription factors in the transition during which proliferating hepatocytes become quiescent. We used primary rat hepatocytes cultured in modified L-15 medium. The cells proliferated and, after the addition of 2% dimethyl sulfoxide (DMSO) from day 4, they stopped growing and gradually differentiated. During hepatic proliferation, expression of hepatocyte nuclear factors (HNF)1alpha, HNF4, C/EBP alpha, and C/EBP beta mRNAs was depressed, whereas that of HNF3alpha and HNF3beta transcripts was enhanced. After the addition of DMSO, the expression of HNF1alpha, HNF3gamma, and HNF4 returned to the level in isolated cells and HNF1beta mRNA expression gradually increased. However, expression of C/EBP alpha and C/EBP beta mRNAs was partially recovered. The mitoinhibitory agents, IL-1beta, IL-6, TGF-beta, and activin A, were examined to determine whether they could induce differentiation of proliferating hepatocytes as shown in cells treated with DMSO. Although these factors inhibited cell growth, the cells did not differentiate. The expression pattern of HNF3gamma mRNA was quite different in the cells cultured with DMSO and those cultured with cytokines. Therefore, hepatic differentiation requires not only inhibition of DNA synthesis but also induction of appropriate transcription factors. Thus, expression of HNF3gamma, C/EBP alpha, and C/EBP beta may be necessary for hepatocytes to acquire highly differentiated functions in addition to coexpression of certain amounts of transcripts of HNF1alpha, HNF1beta, HNF3alpha, HNF3beta, and HNF4 as well as suppression of C/EBP delta.