Selective protection of murine cerebral Gi/o-proteins from inactivation by parenterally injected pertussis toxin.

ABSTRACT

Pertussis toxin (PTX) is a potent virulence factor in patients suffering from whooping cough, but in its detoxified version, it is applied for vaccination. It is thought to contribute to the pathology of the disease including various CNS malfunctions. Based on its enzymatic activity, PTX disrupts GPCR-dependent signaling by modifying the α-subunit of heterotrimeric Gi/o-proteins. It is also extensively used as a research tool to study neuronal functions in vivo and in vitro. However, data demonstrating the penetration of PTX from the blood into the brain are missing. Here, we examined the Gαi/o-modifying activity of PTX in murine brains after its parenteral application. Ex vivo biodistribution analysis of [124I]-PTX displayed poor distribution to the brain while relatively high concentrations were visible in the pancreas. PTX affected CNS and endocrine functions of the pancreas as shown by open-field and glucose tolerance tests, respectively. However, while pancreatic islet Gαi/o-proteins were modified, their neuronal counterparts in brain tissue were resistant towards PTX as indicated by different autoradiographic and immunoblot SDS-PAGE analyses. In contrast, PTX easily modified brain Gαi/o-proteins ex vivo. An attempt to increase BBB permeability by application of hypertonic mannitol did not show PTX activity on neuronal G proteins. Consistent with these findings, in vivo MRI analysis did not point to an increased blood-brain barrier (BBB) permeability following PTX treatment. Our data demonstrate that the CNS is protected from PTX. Thus, we hypothesize that the BBB hinders PTX to penetrate into the CNS and to deliver its enzymatic activity to brain Gαi/o-proteins. KEY MESSAGES i.p. applied PTX is poorly retained in the brain while reaches high concentration in the pancreas. Pancreatic islet Gαi/o- but not cerebral Gαi/o-proteins are modified by i.p. administered PTX. Gαi/o-proteins from isolated cerebral cell membranes were easily modified by PTX ex vivo. CNS is protected from i.p. administered PTX. PTX does not permeabilize the BBB.