Pharmacological CD206 blocking attenuates cell-free hemoglobin-induced liver damage in sickle cell disease

Abstract Introduction: Hemolysis and accumulation of cell-free hemoglobin (Hb) are major pathophysiological complications associated with sickle cell disease (SCD). In the absence of a functional spleen, hepatic Kupffer cells play a large role in Hb clearance. Recently, we demonstrated that along with Kupffer cells, liver sinusoidal endothelial cells (LSECs) also accumulate Hb. However, persistent Hb accumulation leads to LSEC senescence and liver damage in SCD. Given that organ damage is a primary cause of hospitalization in SCD patients, elucidating the mechanism of LSEC Hb buildup may yield valuable therapeutic insights for SCD.Method: As LSECs are not classically involved in Hb clearance, we performed a small-molecule inhibitor screen in vitro in primary LSECs and in vivo in humanized Townes SCD mouse model to identify the mechanism of LSEC-mediated Hb clearance.Results: Among the pharmacological blockers we examined, inhibition of mannose receptor CD206 demonstrated significantly reduced internalization of HbS to LSECs. Moreover, administration of a specific CD206 inducer RP182 demonstrated exacerbated HbS internalization in LSECs, suggestive of a potential role of CD206 in the regulation of LSEC Hb accumulation. Accelerated Hb-heme clearance in the liver may result in liver injury resolution by rapid clearance of the dead cells. Immunohistochemical analysis by H&E and trichome staining showed amelioration of liver fibrosis in CD206 blocker-treated SCD mice compared to sham-treated SCD mice. Prussian blue staining revealed a strong reduction in the number of iron-positive vesicles in CD206-inhibited SCD mice, as compared to sham-treated SCD mice. Amelioration of liver injury was further confirmed by the downregulation of mRNA encoding for fibrosis markers (collagen 1A1, 1A2, and 4) in SCD+CD206 blocker mice as compared with SCD mice at baseline. Consistent with reduced liver fibrosis, blocking of CD206 significantly lowered hepatic expression of VCAM1, VCAM2, and TLR4, suggesting that CD206 inhibition diminishes oxidative stress in LSECs of SCD mice. Complete blood cell-count analysis demonstrated increased plasma Hb level in SCD mice post-CD206 administration, indicative of reduced hemolysis. This was further confirmed by a significant increase in mean corpuscular hemoglobin (MCH) content, hematocrit values, and mean corpuscular volume (MCV) values, which were all upregulated in SCD mice post-CD206 blocking treatment. Mechanistically we found that CD206 caused reduced inflammation, iron accumulation, and oxidative stress in SCD mice liver. Research is currently underway to identify the molecular mechanism by which CD206 induces oxidative stress and sterile inflammation resulting in LSEC Hb accumulation and liver damage.Conclusion: These data suggest that pharmacological blocking of CD206 warrants further clinical evaluation as a therapeutic strategy for the amelioration of cell-free hemoglobin-induced organ damage in SCD.