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Interleukin-1 receptor in sickle cell disease
Figure 6. Post-stroke macrophage infiltration in response to anakinra. Representative staining immunopositive to MAC3 in the peri-infact area of Wt,SCDbmt given one intraperitoneal injection of phosphate buffered saline (PBS) or anakinra immediately post-stroke induction, and quantification of MAC3-positive cells (mean ± standard deviation). A Nikon SE upright microscope and a Nikon DS-Fi3 camera was used to capture 10x and 20x images of ipsilateral brain and 10x images of con- tralateral brain. Dotted line denotes transition between infarcted area and heathy tissue. **P<0.01 as determined by student’s t-test.
decreasing adhesion molecules such as E-selectin and ICAM-1,56 and also by preservation of BBB integrity. Although some studies have shown BBB integrity may be preserved by the action of macrophages,35 this study demonstrated that macrophages recruited acutely through IL-1R pathways may be deleterious. Long term human studies targeting IL-1β in SCD will be informative. A clin- ical study with the IL-1β antagonist, canakinumab, is cur- rently underway to determine safety and efficacy of IL-1β inhibition in SCD patients (clincialtrials gov. Identifier: NCT02961218).
The beneficial effects of IL-1R inhibition observed in this study are independent of non-hematopoietic IL-6. In response to ischemia, neurons and other cell types in the brain produce IL-6,58,59 and circulating IL-6 concentrations have been positively associated both with stroke size in patients,60 and with worsening outcomes within 48 hours post-stroke.61 While IL-6 may adversely affect stroke acutely.23,59 IL-6 may show beneficial effects towards res- olution of stroke damage.62 The assessment of stroke vol- ume 72 hours after stroke induction in this study may have been too early to observe the full effects of IL-6 towards stroke repair. However, the failure of IL-6-/-,SCDbmt mice to phenocopy IL1R-/-,SCDbmt mice in relation to stroke size illustrates the lack of dependence on the downstream induction of IL-6 toward the acute detri- mental action of IL-1R signaling.
While chronic treatment of SCD patients with anti- cytokine therapies may increase susceptibility to infec- tions, short term treatment could be administered to patients presenting with acute complications. Remarkably, the IL-1R antagonist, anakinra, was benefi- cial even when administered following onset of MCA occlusion. These findings suggest that targeting the IL-1R may be beneficial in SCD patients presenting with stroke or other vascular complications.
Limitations of this work include the use of BMT to gen- erate chimeric mice. It is possible the irradiation procedure used to ablate the bone marrow could have affected the vascular phenotypes, however, this strategy has been widely employed and greatly facilitates the generation of chimeric SCD mice.63-65 It is also possible that other bene- ficial effects of chimeric IL-1R deficiency in this model are
at play. Although there were no differences in anemia between different recipient transgenic mice receiving sickle cell marrow, we cannot rule out differences in engraftment related to recipient IL-1R status. Future experiments with mice generated by crossbreedings to produce complete and tissue-specific gene deletions will be useful to confirm and expand these studies. The stroke model used in this study is induced by MCA thrombotic occlusion. A more relevant model would include spontaneous stroke due to vaso- occlusion triggered by sickled erythrocytes. However, well validated models of spontaneous stroke are not available in SCD mice to our knowledge. Additionally, we cannot rule out differences in blood flow following MCA occlusion due to difference in IL-1R signaling. These studies would require a time course analysis after stroke induction in addition to laser doppler imaging. While there is no stan- dard drug for treatment of acute stroke associated with sickle cell disease, future experiments comparing anakinra with tissue plasminogen activator or emergent blood trans- fusion would be interesting. Finally, longer periods between stroke induction and stroke volume measurement may be informative.
In conclusion, non-hematopoietic deficiency of the IL-1R is sufficient to reduce stroke size in SCD. Therapies targeting this pathway may be beneficial towards the treat- ment of stroke and possibly other complications of SCD.
Disclosures
No conflicts of interest to disclose..
Contributions
DTE contributed to the conception and experimental design of this work; JV, JW, JM and CG contributed to the acquisition of data; JV and JM were responsible for data analysis; DTE and JV contributed to the interpretation of the data, drafting and revi- sion of the manuscript; DTE approved the final version of the work and agrees to be accountable for aspects of the work.
Funding
This work was supported by the National Institutes of Health (T32-HL007853 to JV. and a VA Merit Award (BX002776 to DTE).
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