Paraoxonase‐1 regulation of Na/K‐ATPase alpha‐1 Src signaling in Chronic Kidney Disease
Authors: Khalaf Fatimah Kareem , Mohammed Chrysan Joy , Dube Prabhatchandra , Connolly Jacob , Kleinhenz Andrew , Malhotra Deepak , Fedorova Olga , Haller Steven , Kennedy David 
Published: April 2020

BackgroundCardiotonic steroids (CTS) are Na/K‐ATPase alpha‐1 (NKA α‐1) ligands that are increased in volume expanded states such as chronic kidney disease (CKD). We have demonstrated that the NKA α‐1‐Src signaling pathway is a critical mediator of CTS induced renal inflammation and oxidative stress in these settings. Paraoxonase‐1 (PON‐1) is a hydrolytic lactonase enzyme which is synthesized in the liver and circulates bound to high‐density lipoprotein. Clinical data demonstrate an association between diminished lactonase activities of PON‐1 and renal disease severity, yet the underlying mechanism(s) are largely unknown. We have identified novel mechanistic link between PONs and endogenous CTS whereby the lactonase activities of PONs hydrolyze CTS to their inactive open‐ring forms which, unlike native CTS, are incapable of stimulating NKA α‐1 and initiating pro‐inflammatory signaling cascades.AimTo test the hypotheses that PON‐1 can attenuate the progression of renal inflammation in CKD through modulating the pathogenic pathways induced by CTS‐NKA α‐1‐Src signaling.Method and ResultsExperiments were performed on control Dahl salt‐sensitive rats (SSMcwi, hereafter called SS rats) and Pon1 knock‐out rats (designated SS‐Pon1em1Mcwi, hereafter called SS‐Pon1 KO rats) generated by injecting a CRISPR targeting the sequence into SSMcwi rat embryos which resulted in a 7bp frameshift insertion in exon 4 of the Pon1 gene. In order to examine the protective role of the PON‐1 in renal disease progression, age‐matched male SSPon1 KO and SS rats were maintained on 8% high salt diet for up to 5 weeks to initiate the salt‐sensitive hypertensive renal disease characteristic of this model. Upon examination we found that, despite similar blood pressure, SS‐Pon1 KO rats showed significant increase in renal inflammation and fibrosis (both p<0.01), decrease in FITC‐Sinistrin glomerular filtration rate (p<0.05), and increased mortality (p<0.01) compared to SS‐rats. Next, in order to examine involvement of the CTS‐NKA α‐1‐Src kinase signaling axis, SS‐Pon1 KO rats were further divided into two subgroups: one group received a specific NKA α‐1‐Src kinase complex inhibitor, pNaKtide (25 mg/kg i.p.), every week for a total of 4 injections, and the second group, received an anti‐CTS monoclonal antibody (3E9 mAb, 50 μg/kg i.p.) every week for a total of 4 injections, with both sub groups were maintained on the same 8% high salt diet. We found that while SS‐Pon1 KO rats on high salt diet demonstrated significant acceleration in renal disease progression as noted by increased renal inflammation, renal fibrosis and mortality as well as decreased renal function, these effects were all significantly (all p<0.05) attenuated by inhibition of the NKA α‐1‐Src signaling pathway via both pNaKtide and anti‐CTS monoclonal antibody.ConclusionOur data suggest PON‐1 is an endogenous counter‐regulatory mechanism of the CTS‐NKA α‐1‐Src signaling axis which can be therapeutically targeted to attenuate hypertensive renal disease.Support or Funding InformationNIH/NHLBI HL‐137004