Abstract
Protein kinase N1 (PKN1) knockout (KO) mice spontaneously form germinal centers (GCs) and develop an autoimmune-like disease with age. Here, we investigated the function of PKN1 kinase activity in vivo using aged mice deficient in kinase activity resulting from the introduction of a point mutation (T778A) in the activation loop of the enzyme. PKN1[T778A] mice reached adulthood without external abnormalities; however, the average spleen size and weight of aged PKN1[T778A] mice increased significantly compared to aged wild type (WT) mice. Histologic examination and Southern blot analyses of spleens showed extramedullary hematopoiesis and/or lymphomagenesis in some cases, although without significantly different incidences between PKN1[T778A] and WT mice. Additionally, flow cytometry revealed increased numbers in B220+, CD3+, Gr1+ and CD193+ leukocytes in the spleen of aged PKN1[T778A] mice, whereas the number of lymphocytes, neutrophils, eosinophils, and monocytes was reduced in the peripheral blood, suggesting an advanced impairment of leukocyte trafficking with age. Moreover, aged PKN1[T778A] mice showed no obvious GC formation nor autoimmune-like phenotypes, such as glomerulonephritis or increased anti-dsDNA antibody titer, in peripheral blood. Our results showing phenotypic differences between aged Pkn1-KO and PKN1[T778A] mice may provide insight into the importance of PKN1-specific kinase-independent functions in vivo.
Highlights
Protein kinase N1 (PKN1) knockout (KO) mice spontaneously form germinal centers (GCs) and develop an autoimmune-like disease with age
Extramedullary hematopoiesis and lymphomagenesis in spleens were observed in some cases; neither phenotype is likely to be an exclusive feature of aged PKN1[T778A] mice responsible for spleen enlargement
We previously reported that lymphocytes from PKN1[T778A] mice at aged 7–9 weeks show lower levels of chemotaxis toward chemokines, such as sphingosine 1-phosphate (S1P), and have a tendency to accumulate in secondary lymphoid organs, likely owing to defective egress from these organs[46]
Summary
Protein kinase N1 (PKN1) knockout (KO) mice spontaneously form germinal centers (GCs) and develop an autoimmune-like disease with age. We found that mice aged 7 to 9 weeks exhibited selective decreases in the number of lymphocytes in peripheral blood and increases in this number in the spleen and lymph nodes in the absence of apparent abnormality in lymphocyte-cell development in the bone marrow and thymus[46] This phenotype appeared to originate via defective lymphocyte egress from secondary lymphoid organs and was supported by significantly lower chemotaxis of lymphocytes deficient in kinase activity toward chemokines, such as sphingosine 1-phosphate (S1P) relative to that observed in wild-type (WT) cells in vitro[46]. We performed phenotypic analysis of aged PKN1[T778A] mice and discussed potential differences in the phenotypes of aged PKN1[T778A] and previously reported Pkn1-KO mice
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