| Diabetic nephropathy (DN) is characterized by renal fibrosis and inflammation. Increasing evidence shows that TGF-beta/Smad signaling plays a critical role in DN. This thesis tested a hypothesis that TGF-beta/Smad signaling may play a central role in diabetic kidney injury and targeting this pathway may represent a novel therapy for DN. The hypothesis was tested in a type-1 model of diabetes induced in Smad7 knockout (KO) or CRP transgene, and the therapeutic potential for DN was examined by overexpressing renal Smad7 or miR-29b in both type-1 or type-2 models of diabetes.;As described in Chapter Three, the protective role and therapeutic potential of Smad7 in diabetic kidney disease was investigated in streptozotocin-induced diabetic model in Smad7 KO mice and in diabetic rats given Smad7 gene transfer using an ultrasound-microbubble-mediated technique. Results showed that Smad7 KO mice developed more severe diabetic kidney injury than wild type (WT) mice as evidenced by a significant increase in microalbuminuria, renal fibrosis, and renal inflammation, which was mediated by enhanced activation of both TGF-beta/Smads and NF-kB signaling pathways. To develop a therapeutic potential for diabetic kidney disease, Smad7 gene was transferred into the kidney, which results in high levels renal Smad7, thereby blocking microalbuminuria, TGF-beta/Smad3-mediated renal fibrosis and NF-kB/p65-driven renal inflammation in diabetic rats.;To test a novel hypothesis that TGF-beta/Smad3-mediated DN via the Smad3-dependent miR-29, in Chapter Four, the role and mechanisms of miR-29b in DN were examined in vitro in a stable mesangial cell line with overexpression or knockdown of miR-29b and the therapeutic effect of miR-29b on DN was developed by delivering a Dox-inducible miR-29b into 10-week db/db mice. Results showed that addition of AGEs induced a loss of miR-29b with increased fibrosis and inflammation in mesangial cells, which was further enhanced with miR-29b knockdown, but inhibited by overexpressing miR-29b. In db/db mice, reduction of renal miR-29b over the 20 week time was associated with a marked increase in microabluminuria, renal fibrosis and inflammation. Restoring miR-29b resulted in inhibition of kidney injuries by blocking TGF-beta/Smad3-mediated renal fibrosis, NF-kB/p65-driven renal inflammation, and importantly, the Th1-dependent immune response, revealing a critical role and therapeutic potential for miR-29b in the pathogenesis of DN.;Finally, diabetic kidney injury was also assessed in under high inflammation conditions in CRP transgenic (Tg) mice. As shown in Chapter Five, CRP Tg mice developed more severe diabetic kidney injury than WT mice, as evidenced by a significant increase in microalbuminuria and kidney injury molecule-1, macrophages and T cells, and upregulation of pro-inflammatory cytokines and extracellular matrix. CRP-mediated DN was associated with upregulation of CRP receptor, CD32a, and over-activation of the TGF-beta/Smads and NFkappaB/p65 signaling pathways. These findings were further confirmed in vitro under high levels of CRP. In addition, CRP was induced by high glucose, which synergistically promoted high glucose-mediated renal inflammation and fibrosis, suggesting a positive feedback-loop between CRP and high glucose under diabetic conditions.;In conclusion, TGF-beta/Smads play critical roles in the pathogenesis of DN. Loss of renal Smad7 and miR-29b may be a key mechanism of DN. Thus, over-expression of Smad7 or miR-29b may represent novel therapeutic strategies for diabetic kidney complications. |
