*Purpose: Although Ikaros is a well-established transcriptional regulator of lymphopoiesis and differentiation of leukocyte lineage, its role in myeloid cells and ischemia reperfusion injury remain unclear. We have reported that the SIRT1 promotes homeostasis and hepatic rejuvenation in mouse and human liver transplantation. Whether SIRT1 signaling is essential in myeloid cell polarization remains uncertain, while the molecular communication between Ikaros and SIRT1 has not been studied.

*Methods: To interrogate the significance of myeloid Ikaros-SIRT1 axis in the context of innate immune activation, comprehensive molecular and functional studies encompassing primary mouse macrophage cultures (siRNA-targeted under LPS/IL4 stimulation), in vivo mouse models of hepatic inflammation (liver warm ischemia-reperfusion injury in WT, myeloid-specific SIRT1-KO, and CD11b-DTR mouse systems), and analyses of human liver transplant patients (fifty-five clinical cases) were undertaken.

*Results: Human LT biopsies were divided into two groups based on Ikaros gene levels (RT-PCR). As compared with the “low” expression group, the “high” Ikaros expressing LTs showed significantly higher sALT at POD1-4, gene expression of M1 markers but lower SIRT1 protein levels in post-transplant livers (n=55, p<0.05). Then, we employed mouse macrophage cultures to assess Ikaros function in innate-immune activation. Ikaros silencing (siRNA) in BMM decreased M1 but increased M2 markers, coinciding with enhanced SIRT1 activation. In contrast, Ikaros overexpression in BMM cultures increased M1 markers and diminished SIRT1, while macrophage-specific SIRT1 deficiency increased M1 but decreased M2 activation markers. mSIRT1-KO mice experienced exacerbated hepatic IRI, accompanied by up-regulated M1 markers (n=7, p<0.05). Depletion of CD11b+ cells suppressed Ikaros expression in IR-stressed livers while BMM reconstitution restored Ikaros levels, implying recruited macrophages were instrumental for hepatic Ikaros expression. Interestingly, reconstitution of CD11b-deficient mice with siRNA-Ikaros BMM ameliorated hepatic IRI with increased levels of SIRT1 and M2 markers as compared with siRNA-control BMM (n=6, p<0.05).

*Conclusions: Our results identify Ikaros as a novel M1 macrophage activation marker and document the Ikaros – SIRT1 signaling axis as a mechanistic biomarker and putative checkpoint regulator of M1/M2 macrophage polarization, with divergent innate phenotypic signatures in sterile inflammation response in liver transplantation.

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