Deletion of Exon I of SMAD7 in Mice Results in Altered B Cell Responses

Abstract

The members of the TGF-β superfamily, i.e., TGF-β isoforms, activins, and bone morphogenetic proteins, regulate growth, differentiation, and apoptosis, both during embryonic development and during postnatal life. Smad7 is induced by the TGF-β superfamily members and negatively modulates their signaling, thus acting in a negative, autocrine feedback manner. In addition, Smad7 is induced by other stimuli. Thus, it can fine-tune and integrate TGF-β signaling with other signaling pathways. To investigate the functional role(s) of Smad7 in vivo, we generated mice deficient in exon I of Smad7, leading to a partial loss of Smad7 function. Mutant animals are viable, but significantly smaller on the outbred CD-1 mouse strain background. Mutant B cells showed an overactive TGF-β signaling measured as increase of phosphorylated Smad2-positive B cells compared with B cells from wild-type mice. In agreement with this expected increase in TGF-β signaling, several changes in B cell responses were observed. Mutant B cells exhibited increased Ig class switch recombination to IgA, significantly enhanced spontaneous apoptosis in B cells, and a markedly reduced proliferative response to LPS stimulation. Interestingly, LPS treatment reverted the apoptotic phenotype in the mutant cells. Taken together, the observed phenotype highlights a prominent role for Smad7 in development and in regulating the immune system’s response to TGF-β.

Profibrogenic transforming growth factor-β/activin receptor-like kinase 5 signaling via connective tissue growth factor expression in hepatocytes

“…29 Briefly, the Smad7 locus was isolated from a 129Sv genomic library. 30 The targeting vector contained a fragment of the Smad7 promoter and 5Ј untranslated leader sequence, followed by a PGKneobpA expression cassette replacing the translated part of exon 1 and the exon I/intron I boundary, a 1-kilobase HindIIINotI genomic 3Ј fragment, and a herpes simplex virus thymidine kinase expression cassette in pBluescript SK ϩ .…”

Low hepcidin accounts for the proinflammatory status associated with iron deficiency

“…The BMP coreceptor hemojuvelin (Hjv) was downregulated after LPS treatment (supplemental Figure 2D), as reported. 5 However, SMAD7, which has been related to the inflammatory pathway, 26 was slightly increased in ID mice after LPS injection ( Figure 3F). …”

Smad7 deficiency decreases iron and haemoglobin through hepcidin up‐regulation by multilayer compensatory mechanisms

“…Thus, Smad7 may serve as a negative feedback regulator of hepcidin expression. Global Smad7 ‐knockout ( Smad7 −/− ) mice have reduced viability,21, 33 impaired cardiovascular development,21 exacerbated liver injury34 and altered immune cell responses 35. To investigate the physiological role of Smad7 in regulating both hepcidin expression and iron metabolism, we generated hepatocyte‐specific Smad7 ‐knockout ( Smad7 Alb/Alb ) mice.…”