Background/Purpose: Neutrophils are the most abundant leukocytes and the first to be recruited to the site of photodamage after ultraviolet B (UVB) exposure. We have shown that UVB induces neutrophil recruitment to the inflamed skin with NET formation and exhibition of NET-associated proinflammatory cytokines. Nuclear envelope rupture is a prerequisite for nuclear DNA release and NET formation. In our latest publication, we have identified that nuclear translocation of PKCα and its mediated lamin B phosphorylation is responsible for nuclear envelope rupture and NETosis. We have shown that application of Rho Kinase (ROCK) inhibitor HA1077 attenuates actin assembly and PKCα nuclear translocation, as well as NETosis in vitro. In our previous work, we found that intraperitoneal application of HA1077 alleviates NETosis in vivo and NET-associated proinflammatory cytokines in skin of the UVB-irradiated C57/BL6 wildtype (WT) mice.  

Methods: In the current study, to further investigate the causal role of ROCK in NET formation and UVB-induced skin inflammation, we have generated CD45.1 mice with hematopoietic specific ROCK1 deficiency by bone marrow transplantation (BMT) of hematopoietic stem cells (HSCs) from ROCK1 deficient mice, and following by UVB exposure (150 mJ/cm², 5 consecutive days). Then we have examined IFNγ, TNFα, IL-17A expression and exhibition with NETs in skin of the UVB-irradiated skin. We also detected NET formation and cytokine release with NETs in platelet-activating factor (PAF) stimulated neutrophils from different groups of mice.

Results: In results, we found that NET formation in vitro triggered by PAF was significantly decreased in neutrophils isolated from ROCK1 deficient mice as compared to those from WT mice. Most importantly, NET formation and NET-associated IFNγ, TNFα, IL-17A were significantly attenuated in skin of UVB-irradiated CD45.1 BMT mice with ROCK1 deficiency as compared to those transplanted with HSCs from WT mice. To address what we saw in vivo, we conducted ex vivo experiment in which exhibition of neutrophil NET-associated IFNγ, TNFα, IL-17A were reduced in PAF-treated neutrophils from ROCK1 deficient mice as compared to those from WT mice.

Conclusion: In conclusion, using mice with hematopoietic specific ROCK1 deficiency, we demonstrated the role of ROCK1 in neutrophil NET formation and NET-associated proinflammatory cytokine display in UVB-induced skin inflammation. In addition, our study provide insight into a potential therapeutic strategy of targeting on ROCK as a novel potential target treatment of neutrophil NET-associated diseases and UVB-induced skin inflammation and the relevant diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/hematopoietic-specific-deficiency-of-rho-kinase-attenuates-neutrophil-netosis-and-uvb-induced-skin-inflammation/