A protective role for CD47 in inhibiting aberrant inflammation and death of Ptpn6spin mice
Creators: name: Mazgaeen, Lalita
Publisher: name: University of Iowa
Year: 2023
Subjects: autoinflammation
Neutrophilic dermatosis
Protein tyrosine phosphatase
Ptpn6 spin
public abstract

description: Neutrophilic dermatoses are rare forms of autoinflammatory skin diseases such as Sweet syndrome, subcorneal pustular dermatosis, and pyoderma gangrenosum which are characterized by dense infiltration of neutrophils. The treatment strategies for these diseases are limited to the use of strong immunosuppressives such as corticosteroids which are non-specific and have adverse side effects. Therefore, specific therapeutic targets are required for better diagnosis and treatment of these diseases. Studies have shown the association of PTPN6 splice variants or heterozygous mutations in the pathogenesis of neutrophilic dermatosis in patients. Mice with SHP1 proteins which have a single amino acid substitution from tyrosine 208 residue to asparagine (hereafter Ptpn6spin mice) develop an autoinflammatory disease with inflamed footpads. Inflamed footpads from these Ptpn6spin mice are replete with neutrophils resembling neutrophilic dermatosis in humans. Previous studies have shown that IL-1α and neutrophils are critical for provoking autoinflammatory disease in these mice. Given the implication of integrins in neutrophil migration and regulation of IL-1α, we hypothesized that CD47, an integrin-associated protein, promotes disease pathogenesis in Ptpn6spin mice. Contrary to our hypothesis, CD47 limited wasting syndrome and fatal disease in Ptpn6spin mice. Genetic crosses to study CD47 function in Ptpn6spin mice bred Ptpn6spin x Cd47−⁄− mice were not born at the expected Mendelian ratio. Ptpn6spin bone marrow cells transferred into lethally irradiated WT mice promote footpad inflammation reminiscent of neutrophilic dermatosis. However, Ptpn6spin bone marrow cells, when transferred into lethally irradiated Cd47-deficient mice, caused dramatic weight loss and subsequent death. At a cellular level, Ptpn6-deficient neutrophils were responsible for the dramatic weight loss and death of the lethally irradiated Cd47−⁄− recipients. Cellular analysis of the spleen from the diseased mice demonstrated significant reduction in splenocyte number that were associated with lymphopenia. Given the marked reduction in splenocyte number and lymphopenia, we posited that leakage of gut microbiota promote morbidity and mortality in Cd47−⁄− mice receiving Ptpn6spin cells. Indeed, colonic cell death was significantly increased in the diseased Cd47−⁄− mice. Furthermore, loss of gut barrier integrity and systemic leakage of gut microbes contributed to the observed morbidity and mortality. Given that CD47 acts as a ‘don’t eat me’ signal for phagocytes and SHP1 negatively regulates inflammation, we speculated that aberrant phagocytosis in the absence of CD47 combined with aberrant inflammation in the absence of SHP1 leads to the morbidity and mortality. Ptpn6spin mice do not exhibit disease-associated mortality which suggests that both aberrant phagocytosis and aberrant inflammation should occur simultaneously to induce inflammation and lethality. Furthermore, we investigated the role of CD47 interacting partners, SIRPα and TSP1 and their cross talk with SHP1 using chimera mice models. Neutralization of SIRPα or its deficiency in the radioresistant compartment was not sufficient to provoke lethal disease observed in Ptpn6spin &gt;&gt; Cd47−⁄− chimeras which suggests that SIRPmay not be important or that other redundant pathways may exist to engage CD47. In contrast, our data demonstrate that TSP1 plays a partial role in lethal disease observed in Ptpn6spin &gt;&gt; Cd47−⁄− chimeras. Importantly, IL-1 signaling blockade using anakinra rescued the morbidity and mortality observed in the Ptpn6spin &gt;&gt; Cd47−⁄− mice. Our data show that IL-1 signaling in both compartments is important to instigate lethal disease in Ptpn6spin x Cd47−⁄− double knock out mice. These data altogether demonstrate a protective role for CD47 in tempering pathogenic neutrophils in the Ptpn6spin mice, and a critical role for IL-1 signaling in lethal inflammatory disease in Ptpn6spin x Cd47−⁄− DKO mice.
description: In conclusion, my thesis project highlights a previous unknown signaling crosstalk between SHP1 and CD47, with CD47 playing an important role in tempering inflammation provoked by SHP1-deficient neutrophils. Herein, we finally show that aberrant IL-1 signaling in the dual absence of SHP1 and CD47 may contribute to morbidity and mortality. Given that CD47 blockade is gaining traction in treatment of different cancers, my study proposes a careful examination of the patient history and genetic status of SHP1 may be warranted before using CD47 blockade treatments to avoid lethal consequences. But importantly, promoting positive CD47 signaling to the disease promoting neutrophils may provide an interesting avenue for therapeutic intervention in humans suffering from these rare disorders.