Fibroblast HDAC1-Mediated Cytokine Contributes to Fibrosis After Kidney Ischemia-Reperfusion Injury

Background: Ischemia-reperfusion injury (IRI) can cause acute kidney injury (AKI) and progression to chronic kidney disease (CKD) that is characterized by renal interstitial fibrosis. Histone deacetylase 1 (HDAC1), an epigenetic regulator of transcription, is activated following IRI and we hypothesize that fibroblast/pericyte HDAC1 activation contributes to in part by enhancing the secretion of pro-inflammatory cytokines and chemokines. Methods: Male HDAC1fl/fl (littermate control) (n=13), and floxed mice positive for hemizygous Col1A2-CreER (iFibHDAC1KO mice) (n=17) were used. All mice received tamoxifen i.p. in adulthood and this resulted in fibroblast/pericyte HDAC1 knockdown in Cre positive mice. Subsets of mice underwent 18-minute kidney bilateral IRI or sham surgery. Acute kidney injury was confirmed 24 hours post-injury by measuring glomerular filtration rate. Interstitial fibrosis was evaluated after four weeks using picrosirius red staining, and quantification of fibronectin, collagen-1, and alpha smooth muscle actin (aSMA. Normal rat kidney fibroblasts (NRK-49F) were transfected with either an empty vector or HDAC1 for 24h. Cytokine/chemokine secretion in the culture media was determined. Results: The severity of the AKI was similar among the genotypes as GFR 24 h post IRI was reduced by ~50% in all mice (p=0.99). Four weeks post-IRI, iFibHDAC1KO mice showed significantly attenuated renal fibrosis compared to control groups (p<0.0001). In the kidney cortex, % fibronectin area in iFibHDAC1KO-IRI (KO-IRI) mice (0.29%+0.23) was significantly lower than control-IRI group (1.11%+0.96, p=0.0055), as was collagen-1 (iFibHDAC1KO-IRI 0.14%+0.073 vs control-IRI 0.33%+0.25, p=0.02). In contrast, αSMA-positive area was not significantly different between genotypes in either the cortex, iFibHDAC1KO-IRI (4.0% ± 3.9) vs control (1.6% ± 1.5, p=0.09). HDAC1 overexpression in NRK-49F cells increased cytokine/chemokine secretion, including 54 pro-inflammatory and 21 anti-inflammatory cytokines/chemokines. Conclusion: Fibroblast-specific HDAC1 knockdown attenuates renal fibrosis after IRI. Conversely, HDAC1 activation is pro-fibrotic by altering cytokine/chemokine secretion toward more inflammatory state, supporting HDAC1 as a potential therapeutic target to prevent fibrosis and AKI-to-CKD progression. Funding: NIDDK Support