Salt inducible kinases 2 and 3 are required for thymic T cell development

Abstract

Salt Inducible Kinases (SIKs), of which there are 3 isoforms, are established to play roles in innate immunity, metabolic control and neuronal function, but their role in adaptive immunity is unknown. To address this gap, we used a combination of SIK knockout and kinase-inactive knock-in mice. The combined loss of SIK1 and SIK2 activity did not block T cell development. Conditional knockout of SIK3 in haemopoietic cells, driven by a Vav-iCre transgene, resulted in a moderate reduction in the numbers of peripheral T cells, but normal B cell numbers. Constitutive knockout of SIK2 combined with conditional knockout of SIK3 in the haemopoietic cells resulted in a severe reduction in peripheral T cells without reducing B cell number. A similar effect was seen when SIK3 deletion was driven via CD4-Cre transgene to delete at the DP stage of T cell development. Analysis of the SIK2/3 Vav-iCre mice showed that thymocyte number was greatly reduced, but development was not blocked completely as indicated by the presence of low numbers CD4 and CD8 single positive cells. SIK2 and SIK3 were not required for rearrangement of the TCRβ locus, or for low level cell surface expression of the TCR complex on the surface of CD4/CD8 double positive thymocytes. In the absence of both SIK2 and SIK3, progression to mature single positive cells was greatly reduced, suggesting a defect in negative and/or positive selection in the thymus. In agreement with an effect on negative selection, increased apoptosis was seen in thymic TCRbeta high/CD5 positive cells from SIK2/3 knockout mice. Together, these results show an important role for SIK2 and SIK3 in thymic T cell development.

Deficiency of salt‐inducible kinase 2 (SIK2) promotes immune injury by inhibiting the maturation of lymphocytes

“…It has been demonstrated that SIK3 is a target of regulating innate immunity 2,13 . Furthermore the absence of SIK2/3 can inhibit the progression to mature single positive T cells 31 . However, the independent effects of SIK2 on immune injury and the maturation of T cells and B cells were not explored before.…”

Salt-inducible kinase 2 regulates fibrosis during bleomycin-induced lung injury

“…It would therefore have been of interest to examine SIK2/3 double knockin mice; however, this was not possible as loss of both SIK2 and SIK3 activity results in embryonic lethality ( 33 ). Furthermore, although mice with a double knockout of both SIK2 and SIK3 in the immune system are viable, they exhibit a failure of thymic T-cell development and very low numbers of peripheral T cells ( 65 ), which would make interpreting the results of bleomycin-induced fibrosis problematic.…”

The multiple roles of salt-inducible kinases in regulating physiology

“…Treatment of the LOUCY acute lymphoblastic leukemia cell line with HG-9-91-01 restored normal T-cell development ( 247 ), therefore suggesting that the SIKs impact lymphoid lineage decision-making via regulating MEF2C activity. Indeed, utilizing a combination of SIK KO and SIK KI mice, Nefla et al ( 248 ) demonstrated that SIK2 and SIK3 are critical regulators of in vivo T-cell development. While SIK2 KI or SIK1/2 double KI mutants had normal T- and B-cell compartments, SIK3 floxed/Vav-iCre animals (where SIK3 is genetically deleted only in hematopoietic cells) displayed slightly reduced T-cell numbers in the spleen and lymph nodes, while B-cell numbers remained unaffected ( 248 ).…”

“…Indeed, utilizing a combination of SIK KO and SIK KI mice, Nefla et al ( 248 ) demonstrated that SIK2 and SIK3 are critical regulators of in vivo T-cell development. While SIK2 KI or SIK1/2 double KI mutants had normal T- and B-cell compartments, SIK3 floxed/Vav-iCre animals (where SIK3 is genetically deleted only in hematopoietic cells) displayed slightly reduced T-cell numbers in the spleen and lymph nodes, while B-cell numbers remained unaffected ( 248 ). Furthermore, SIK2 KO/SIK3 floxed/Vav-iCre double mutant animals had normal peripheral B-cell numbers but drastically reduced T-cell counts in the thymus, spleen, and lymph nodes, with most of any remaining cells displaying an immature phenotype ( 248 ).…”