SMAD3-dependent and -independent pathways in glomerular injury associated with experimental glomerulonephritis.

Glomerulonephritis (GN) is a common cause of end-stage kidney disease and is characterized by glomerular inflammation, hematuria, proteinuria, and progressive renal dysfunction. Transforming growth factor (TGF)-ß is involved in glomerulosclerosis and interstitial fibrosis. TGF-ß activates multiple signaling pathways, including the canonical SMAD pathway. We evaluated the role of SMAD signaling in renal injury and proteinuria in a murine model of GN. SMAD3+/+ or SMAD3-/- mice received anti-glomerular basement membrane antibodies to induce GN. We confirmed previous reports that demonstrated that SMAD3 is an important mediator of glomerulosclerosis and renal interstitial fibrosis. Proteinuria was highly SMAD3 dependent. We found differential effects of SMAD3 deletion on podocytes and glomerular endothelial cells. GN led to podocyte injury, including foot process effacement and loss of podocyte-specific markers. Interestingly, these changes were not SMAD3 dependent. Furthermore, there were significant changes to glomerular endothelial cells, including loss of fenestrations, swelling, and basement membrane reduplication, which were SMAD3 dependent. Despite ongoing markers of podocyte injury in SMAD3-/- mice, proteinuria was transient. Renal injury in the setting of GN involves TGF-ß and SMAD3 signaling. Cell populations within the glomerulus respond differently to SMAD3 deletion. Proteinuria correlated more with endothelial cell changes as opposed to podocyte injury in this model.

Gremlin promotes peritoneal membrane injury in an experimental mouse model and is associated with increased solute transport in peritoneal dialysis patients.

The peritoneal membrane becomes damaged in patients on peritoneal dialysis (PD). Gremlin 1 (GREM1) inhibits bone morphogenic proteins (BMPs) and plays a role in kidney development and fibrosis. We evaluated the role of gremlin in peritoneal fibrosis and angiogenesis. In a cohort of 32 stable PD patients, GREM1 concentration in the peritoneal effluent correlated with measures of peritoneal membrane damage. AdGrem1, an adenovirus to overexpress gremlin in the mouse peritoneum, induced submesothelial thickening, fibrosis, and angiogenesis in C57BL/6 mice, which was associated with decreased expression of BMP4 and BMP7. There was evidence of mesothelial cell transition to a mesenchymal phenotype with increased α smooth muscle actin expression and suppression of E-cadherin. Some of the GREM1 effects may be reversed with recombinant BMP7 or a pan-specific transforming growth factor ß (TGF-ß) antibody. Neovascularization was not inhibited with a TGF-ß antibody, suggesting a TGF-ß-independent angiogenic mechanism. Swiss/Jackson Laboratory (SJL) mice, which are resistant to TGF-ß-induced peritoneal fibrosis, responded in a similar fashion to AdGrem1 as did C57BL/6 mice with fibrosis, angiogenesis, and mesothelial-to-mesenchymal transition. GREM1 was associated with up-regulated TGF-ß expression in both SJL and C57BL/6 mice, but SJL mice demonstrated a defective TGF-ß-induced GREM1 expression. In summary, GREM1 induces fibrosis and angiogenesis in mouse peritoneum and is associated with increased solute transport in these PD patients.

Adenovirus-mediated gene transfer of TGF-ß1 to the renal glomeruli leads to proteinuria.

The mechanism of proteinuria in many common kidney diseases involves glomerular hemodynamic effects and local expression of angiogenic, fibrogenic, and vasoactive factors. Transforming growth factor (TGF)-ß has been associated with many diseases involving proteinuria and renal fibrosis. TGF-ß has been shown to induce podocyte dedifferentiation in vitro, but its in vivo effects on the glomerular filtration barrier are not well described. In this study, we used an adenovirus vector to transfer active TGF-ß1 to the glomeruli of rat kidneys. Transient TGF-ß1 overexpression induced significant proteinuria, podocyte foot process effacement, nephrin down-regulation, and nephrinuria. The expression of synaptopodin was also significantly down-regulated by TGF-ß1. Increased glomerular expression of Snail, suggestive of an in vivo dedifferentiation process, was associated with a loss of podocyte epithelial markers. The expression of angiopoietin-1 and angiopoietin-2 was significantly increased in TGF-ß1-transfected glomeruli, and TGF-ß1 increased the expression of the angiopoietin receptor, Tie2, in podocyte cell culture. TGF-ß1 down-regulated nephrin and synaptopodin expression in podocytes in cell culture; this effect was reversed by the blockade of both angiopoietin and Tie2 activities. These findings suggest that locally produced TGF-ß1 can cause podocyte dedifferentiation marked by a loss of synaptopodin, nephrin, and foot process effacement, partly regulated by angiopoietins. This process represents a novel pathway that may explain proteinuria in a variety of common renal diseases.

Rhabdomyolysis-induced acute kidney injury in a patient with non-compliance to levothyroxine therapy.

SUMMARY: Hypothyroidism is a common medical condition and is often easily managed with excellent outcomes, when treated adequately. Compliance with levothyroxine (LT4) therapy is often compromised because of the need for a daily and lasting schedule. Overt rhabdomyolysis due to under-treatment or non-compliance is a rare occurrence. We report a case of rhabdomyolysis leading to acute kidney injury (AKI) on chronic kidney disease (CKD) requiring hemodialysis (HD) in a 68-year-old Caucasian male due to non-compliance with levothyroxine (LT4) therapy. Our patient 'ran out of levothyroxine' for approximately 4 weeks and developed gradually progressive muscle pain. The diagnosis of severe AKI due to rhabdomyolysis was made based on oliguria, elevated creatinine kinase (CK), and renal failure. Resuming the home dose of LT4 failed to correct CK levels, and there was a progressive decline in renal function. Although increasing doses of LT4 and three cycles of HD improved CK levels, they remained above baseline at the time of discharge. The patient recovered gradually and required HD for 4 weeks. CK levels normalized at 6 weeks. Through this case report, we highlight that non-compliance with LT4 therapy can lead to life-threatening complications such as renal failure and hence the need to educate patients on the significance of compliance with LT4 therapy should be addressed. LEARNING POINTS: Non-compliance to levothyroxine therapy is common and can lead to serious complications, including rhabdomyolysis. Rhabdomyolysis is an uncommon presentation of hypothyroidism and severe rhabdomyolysis can result in renal failure requiring hemodialysis. Rhabdomyolysis associated with hypothyroidism can be further exacerbated by concomitant use of statins.

Prolonged peritoneal gene expression using a helper-dependent adenovirus.

BACKGROUND: Encapsulating peritoneal sclerosis (EPS) is a rare complication of peritoneal dialysis. The causes of EPS are not well defined and are likely multifactorial. A suitable animal model would facilitate research into the pathophysiology and treatment of EPS. METHODS: We developed a helper-dependent adenovirus that expresses both green fluorescent protein (GFP) and active transforming growth factor-beta (TGF-beta1; HDAdTGF-beta1). Mice were administered HDAdTGF-beta1 via intraperitoneal injection and the response was compared with mice administered either first-generation adenovirus expressing TGF-beta1 (AdTGF-beta1) or control adenovirus (AdGFP). RESULTS: HDAdTGF-beta1-treated mice continued to express the GFP reporter transgene to day 74, the end of the observation period. Transgene expression lasted less than 28 days in the animals treated with first-generation adenoviruses. Animals treated with first-generation AdTGF-beta1 demonstrated submesothelial thickening and angiogenesis at day 7, with almost complete resolution by day 28. The HDAdTGF-beta1-treated mice demonstrated progressive peritoneal fibrosis with adhesion formation and encapsulation of bowels. Weight gain was significantly reduced in animals treated with HDAdTGF-beta1 compared to both the control-treated animals and the AdTGF-beta1-treated animals. Inflammation was not a major component of the fibroproliferative response. CONCLUSIONS: Peritoneal administration of a first-generation AdTGF-beta1 leads to transient gene expression, resulting in a resolving fibrotic response and histology similar to that seen in simple peritoneal sclerosis. Prolonged TGF-beta1 expression induced by the helper-dependent HDAdTGF-beta1 led to changes in peritoneal morphology resembling EPS. This suggests that TGF-beta1 may be a contributing factor in both simple peritoneal sclerosis and EPS. This model will be useful for elucidation of the mechanism of EPS and evaluation of potential treatment.

SREBP-1 is a novel mediator of TGFß1 signaling in mesangial cells.

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. Recent studies showed that overexpression of the transcription factor SREBP-1 induces glomerulosclerosis. TGFß1 is a key profibrotic mediator of glomerulosclerosis, but whether SREBP-1 regulates its effects is unknown. In kidney mesangial cells and in vivo, TGFß1 activates SREBP-1. This requires SCAP, S1P, and PI3K/Akt signaling, but is independent of Smad3. Activation of the TGFß1-responsive reporter plasmid p3TP-lux requires SREBP-1a, but not SREBP-1c, binding to an E-box adjacent to a Smad-binding element. SREBP-1a overexpression alone activates p3TP-lux. Smad3 is required for SREBP-1a transcriptional activation and TGFß1 induces association between the two transcription factors. SREBP-1a K333 acetylation by the acetyltransferase CBP is required for Smad3 association and SREBP-1 transcriptional activity, and is also required for Smad3 transcriptional activity. Thus, both Smad3 and SREBP-1a activation cooperatively regulate TGFß transcriptional responses. SREBP-1 inhibition provides a novel therapeutic strategy for diabetic kidney disease.

Transforming growth factor-beta and the glomerular filtration barrier.

The increasing burden of chronic kidney disease worldwide and recent advancements in the understanding of pathologic events leading to kidney injury have opened up new potential avenues for therapies to further diminish progression of kidney disease by targeting the glomerular filtration barrier and reducing proteinuria. The glomerular filtration barrier is affected by many different metabolic and immune-mediated injuries. Glomerular endothelial cells, the glomerular basement membrane, and podocytes-the three components of the filtration barrier-work together to prevent the loss of protein and at the same time allow passage of water and smaller molecules. Damage to any of the components of the filtration barrier can initiate proteinuria and renal fibrosis. Transforming growth factor-beta (TGF-ß) is a pleiotropic cytokine strongly associated with the fibrogenic response. It has a known role in tubulointerstitial fibrosis. In this review we will highlight what is known about TGF-ß and how it interacts with the components of glomerular filtration barrier and causes loss of function and proteinuria.