Protein kinase G Ialpha disulfide oxidation and the pathogenesis of sepsis

Sepsis, often referred to as blood poisoning, occurs when bacteria get into the blood stream. This is a very common disease and when it occurs the chances of survival are rather poor. Major issues in sepsis are that the patient blood pressure becomes very low and their blood vessels become leaky. Together this causes a lot of harm and many of the bodies organs are not supplied with enough blood and so they become injured. Recently we identified a new pathway that lowers blood pressure in healthy people. We have some preliminary evidence this mechanism becomes overactive in sepsis to uncontrollably and overly lower blood pressure. We will test if this is true and try and identify strategies that prevent this from happening as these may be protective to humans with sepsis.

Sepsis is a common and often deadly medical condition that exerts an enormous burden on healthcare systems. Previously we showed that PKGIalpha can be activated by oxidative stress independently of the classical NO-cGMP activation pathway. This alternate activation pathway involves oxidants inducing a disulfide bond between the kinases two subunits. This is potentially relevant to sepsis as it is a time of oxidative stress that may drive formation of the disulfide and this would explain the associated hypotension that causes injury. Consistent with these ideas we have found PKG disulfide formation occurs in mice following LPS treatment, which strongly supports overall hypothesis. Recently we generated 'redox dead' Cys42Ser PKG knock-in mice that cannot be activated by disulfide oxidation. We propose to compare the response of these mice to their wild-type littermate controls during sepsis. We predict that the knock-in will be protected from sepsis-induced hypotension, as will cardiac, lung and kidney function. Indeed our pilot studies have already shown that the knock-in mice are protected in part from LPS-induced hypotension.

Sepsis is a common and often deadly medical condition that exerts an enormous burden on healthcare systems and society. Current therapeutic strategies of administering antibiotics (to combat the underlying infection) or vasopressor (to elevate blood pressure) are often ineffective, with a high risk (approximately 25%) of mortality. In recent years much attention has been paid to the idea that injury during sepsis is driven by over-production of nitric oxide to detrimentally lower blood pressure by activating soluble Guanylate Cyclase and then protein kinase G (PKG). However, clinical trials preventing nitric oxide production during sepsis were ineffective and in fact increased mortality. Clearly our current understanding of the disease is lacking. By better understanding the mechanisms that underlie the dysfunction that occurs in sepsis we improve our chances of implementing or designing rational therapeutic strategies. Our previous work identified an important new way of activating PKG independently of the nitric oxide pathway, involving it becoming oxidised to form an interprotein disulfide. Sepsis is well-known as a time of oxidative stress and so PKG oxidation may be expected to occur. PKG oxidative activation would logically explain the hypotension that occurs during sepsis. Indeed, we found sepsis induces PKG oxidation and this was associated with murine hypotension in vivo. In contrast a Cys42Ser PKG knock-in mouse that cannot be activated by disulfide oxidation was resistant in part to sepsis-induced hypotension. This knock-in model will be invaluable in determining the importance of PKG oxidation in injury during sepsis, as well as helping us understand this at the molecular level. Indeed, by comparing the knock-in responses to their wild-type littermate controls during sepsis, we may be able to identify protective pharmacological treatment that operate by preventing oxidation-induced over-activation of PKG. Overall we have identified a potentially important new mechanism that may be injurious during sepsis, and we propose studies that may lead to therapies that help treat this major healthcare problem.