Loss of hepatocyte co‐operative activity after inhibition of ganglioside GM1 synthesis and shedding

Abstract

Pretreatment of hepatocyte cultures with 1 microM d-l-threo-1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol-HCL (PPPP) for 24 h decreased the ganglioside GM1 content of the cells by approximately 50% and that of the conditioned medium by 90%. No rhythm in the rate of protein synthesis was detected in dense cultures pretreated with PPPP, but was observed in control dense cultures. Conditioned medium from control dense cultures induced synchrony in sparse cultures, which were non-synchronous in their own medium. In contrast, conditioned medium from dense cultures pretreated with PPPP did not synchronize sparse cultures. Since protein synthesis rhythm is a marker of cell synchronization, i.e. their co-operative activity, then non-oscillatory behavior means loss of cell co-operation. The protein synthesis rhythm was restored 24 h after hepatocytes were transferred to PPPP-free medium. Restoration was more rapid when 0.9 microM gangliosides (standard mixture from bovine brain) were added to the medium just after the withdrawal of PPPP. These novel results concerning the loss of rhythm of protein synthesis in low GM1 ganglioside medium support the conclusion that ganglioside is implicated in the regulation of cell co-operative activity.

Shedding and uptake of gangliosides and glycosylphosphatidylinositol-anchored proteins

“…In addition to its role in the modulation of lipid rafts, shedding and uptake of gangliosides and GPI-linked proteins might be involved in some other processes. For example it was hypothesized that shed gangliosides might be involved in cell synchronization [270,271]. The fact that shed ganglioside suppress immune response to cancer cells suggest that this mechanism could actually be used to suppress autoimmune response in some situations.…”

Small cooperative activity of old rat hepatocytes may depend on composition of the intercellular medium

“…3). Control cultures maintained in serumfree medium showed the usual straight-line protein synthetic kinetics (see Brodsky et al, 2000Brodsky et al, , 2003a. Maintaining similar cultures for 30 min in medium with 10% serum from 3-month-old rats resulted in a prominent rhythm with 52-71% mean amplitude, i.e.…”

“…The assumption has been experimentally proved for cell cooperation during formation of a common rhythm in protein synthesis in cultured rat hepatocytes. Exogenous gangliosides synchronize these oscillations; inhibition of the ganglioside synthesis in cells and release from the cells into the medium (shedding) disturbs the synchronization; experimental increase of calcium ions in cytoplasm initiated the rhythm in non-synchronous cultures; and inhibition of calcium fluxes resulted in loss of the rhythm in synchronous cultures (Brodsky et al, 2000(Brodsky et al, , 2003a. Hepatocytes are mature and represent a largely non-proliferating cell population.…”

Melatonin as the most effective organizer of the rhythm of protein synthesis in hepatocytes in vitro and in vivo

“…One micromolar PPPP for 1 day diminished ganglioside content in the conditioned culture medium by >90%. Inhibition of ganglioside synthesis and shedding resulted in the loss of rhythm in dense spontaneously synchronous cultures (Brodsky et al, 2003a). Addition of 2 μM phenyleprine for 2 min to the medium of ganglioside‐blocked cultures restored the rhythm.…”