**3. ADAMs and ADAMTSs in chronic kidney diseases**

#### **3.1 ADAMs in diabetic nephropathy**

There is increasing evidence on the pathophysiological role of ADAM17 (TACE), ADAM19, ADAMTS-13 in CKD.

ADAM17 is a most well-studied sheddase enzyme. It was originally identified as the tumor necrosis factor (TNF)- converting (or activating) enzyme [22] or TACE. It cleaves cell surface molecules, most importantly cytokines and growth factors [39]. By activating EGFR ligands and TNF- ADAM17 has a central role in inflammatory and proliferative processes both of which have crucial role in the development of CKD (Figure 2).

Fig. 2. Role of ADAM17 in CKD.

highly expressed in the mesenchyme of the developing kidney [30]. However, as of present,

Targeted knockout of Adamts-1 in mice showed that the enzyme has an important role in kidney development. Deletion of exon 2 (encoding part of the metalloenzyme domain) resulted in lack of ADAMTS-1 protein in mice and high perinatal lethality of the animals due to kidney malfunction [36]. In these animals both the cortical and medullary areas were reduced with concomitant increase in the caliceal space. Another group found that lack of the whole metalloenzyme domain (deletion of exon 2-4) rendered ADAMTS-1 catalytically inactive which resulted in enlarged renal calices and fibrosis of the uteropelvic junction [37]. These animals also developed bilateral hydronephrosis and papillary atrophy shortly after birth [38]. Since normally there is a high level of ADAMTS-1 expressed in the epithelium of the collecting ducts and of the uteropelvic junction, and because the phenotype greatly resembles to symptoms of the human uteropelvic obstruction, these animals can be good

These data also show that targeting strategies can greatly influence the evolving

There is increasing evidence on the pathophysiological role of ADAM17 (TACE), ADAM19,

ADAM17 is a most well-studied sheddase enzyme. It was originally identified as the tumor necrosis factor (TNF)- converting (or activating) enzyme [22] or TACE. It cleaves cell surface molecules, most importantly cytokines and growth factors [39]. By activating EGFR ligands and TNF- ADAM17 has a central role in inflammatory and proliferative processes

**3. ADAMs and ADAMTSs in chronic kidney diseases** 

both of which have crucial role in the development of CKD (Figure 2).

there is no detail about how knocking down ADAMs influence kidney development.

models for this genetic disease.

**3.1 ADAMs in diabetic nephropathy** 

Fig. 2. Role of ADAM17 in CKD.

phenotypes.

ADAMTS-13 in CKD.

Besides initiating inflammation, TNF has important pathophysiological role in insulin resistance (reviewed in [40]). After activation by ADAM17, the soluble homotrimer of TNF activates the TNF receptor and downstream signaling molecules. Activation of the MAP kinase pathway initiates serine phosphorylation of the insulin receptor substrate (IRS) intracellularly. Being phosphorylated on serine inhibits tyrosine phosphorylation of the IRS which results in insensitivity of the insulin receptor to extracellular insulin and contributes the development of diabetes (Figure 3).

Fig. 3. Mechanism of TNF-induced insulin resistance

ADAM Proteases as Novel Therapeutic Targets in Chronic Kidney Disease 7

secreted ADAMTS-1 of cultured epithelial cells decreased proliferation of a tubular fibroblast

Autosomal-recessive polycystic kidney disease (AR-PKD) is one of the most common genetic disorders of the kidney results in end-stage renal disease. This disease leads to rapid enlargement of the kidney through massive cysts formation. The main pathogenic process in cyst development is the overactivation of the mislocalized EGFR in the cystic apical epithelia (for review see [50]). Excessive shedding of the pro-proliferative growth factor, transforming growth factor (TGF) was also observed. Since secretion of TGFis regulated by ADAM17, therapeutic potential of ADAM17 inhibitors were explored and established in the *bpk* murine model of AR-PKD [51]. In a later study, the role of TGF was not confirmed even if ADAM17

**3.5 Thrombotic thrombocytopenic purpura (TTP)/ haemolytic-uremic syndrome (HUS)**  Thrombotic thrombocytopenic purpura/haemolytic uremic syndrome are often considered variants of a disease characterized by microangiopathic haemolytic anaemia [53]. Platelets are consumed by spontaneously developing microscopic thrombosis. ADAMTS-13, the enzyme which normally processes the very large von Willebrand factor (vWF) is missing [54] or disabled [55, 56] in this disease. Therefore, the very large vWF "capture" circulating platelets and initiates microthrombi formation. The red blood cells passing through the damaged arteries experience excessive shear stress which leads to haemodialysis. Besides purpura and anaemia there are often fever and neurologic symptoms present and the disease can lead to both acute kidney failure and CKD [57, 58]. Interestingly, a recent study which investigated plasma level of vWF in patients with chronic kidney disease of different origin found decreased level of vWF-cleaving protease [59]. Level of vWF was higher in stage IV patients compared to stages II and III, but whether the increased vWF contributed

Several ADAM enzymes were upregulated at the message level in human renal cell carcinomas. Compared to normal tissue mRNA levels of ADAM8, -17, -19, -28 as well as ADAMTS-2 were upregulated. Interestingly, mRNA level of ADAMTS-1 did not change [60]. In other studies, ADAM10 [61] and ADAM9 expression was increased in renal cancer cells and associated with tumor progression [62] suggesting that expression of these enzyme may be used as tumor markers. ADAM15 and -17 contributed to the migratory potential of kidney cancer cells through activation of the EGFR [63] and ADAM17 silencing disabled the capability of renal carcinoma cells to form in vivo tumors [64]. Therefore these enzymes

ADAM and ADAMTS families include growing number of metalloenzymes which have important role in kidney development and are indispensable to normal kidney function.

cell line which suggested that ADAMTS-1 may have anti-fibrotic effect [49].

inhibitors were beneficial for attenuating cyst development in AR-PKD [52].

**3.4 ADAMs in polycystic kidney disease (PKD)** 

to the worsening of CKD is currently not known.

seem to have direct role in renal cancer pathophysiology.

**4. ADAMs in kidney cancer** 

**5. Conclusion** 

High glucose was also shown to promote heparin-binding growth factor (HB-EGF) shedding through ADAM17 activation, however the exact mechanism is unknown [41].

Since ADAM17 activates secretion of TNF, pharmacological inhibitors of the enzyme were tested on blood glucose regulation in animal model of non-obesity-related insulin resistance (fructose-fed rats). ADAM17 inhibitor restored the animals' insulin resistance [42]. In another study, animals heterozygous for ADAM17 (+/-) proved to be relatively protected from high-fat diet-induced obesity and diabetes [43].

A close structural relative of ADAM17, ADAM10 is involved in shedding of RAGE: receptor for advanced glycation end products [44]. Since soluble RAGE can block pathophysiological processes initiated by RAGE, ADAM10 activation may slow down development of diabetes.

As of today, we do not have data on the pathophysiological role of ADAMTS enzymes in diabetes mellitus.

#### **3.2 ADAMs in renal transplant dysfunction and ischemia reperfusion injury**

In vitro studies modelling mechanisms of transplant rejection showed that the mRNA expression of ADAM17 was upregulated in the kidney and that the protein expression of the enzyme was localized next to TNF receptor II. This suggested that ADAM17 may antagonize the effect of TNF by shedding of its receptor during transplant rejection and therefore higher ADAM17 activity might be beneficial [45]. On the other hand, ADAM17 also co-localized with HB-EGF in experimental ischemia-reperfusion injury which suggested that increased shedding of the growth factor may have contributed to the observed fibrotic injury [46]. Pharmacological inhibitors targeting ADAM17 activity reduced renal tissue injury associated with reperfusion. This confirmed that the increased enzyme activity was a cause rather than the consequence of the tissue injury [47].

Another ADAM enzyme, ADAM19 was also implicated in allograft nephropathy however, we do not know any mechanistic details of its actions [48].

#### **3.3 ADAMs in renal fibrosis**

Renal fibrosis is a manifestation of several pathological processes. Glomerular fibrosis can be induced by over-activation of the renin-angiotensin system, and the developing fibrosis and inflammation can be successfully attenuated by ADAM17 inhibitors in animal models of the injury [7]. We showed previously that serotonin-induced mesangial cell proliferation, which is an important component of glomerular fibrosis, can be inhibited by knocking down ADAM17 expression and inhibiting the enzyme activity [9]. On the other hand, we also found that ADAM17 can protect glomerular function by decreasing podocyte permeability through inducing re-arrangement of the zonula occludens protein ZO-1 [8]. These data suggest that depending on the cellular context the enzyme can have different effect on the renal function. Nonetheless, inhibitors of ADAM17 decreased infiltration of macrophages both in the glomeruli and in the interstitium in models of kidney fibrosis [7, 46] proving that targeting ADAM17 can be beneficial for preserving renal function.

There is very few data available on ADAMTS enzymes and renal fibrosis. Unilateral ureteral obstruction in rat induced upregulation of ADAMTS-1 in the tubular epithelial cells. Further, secreted ADAMTS-1 of cultured epithelial cells decreased proliferation of a tubular fibroblast cell line which suggested that ADAMTS-1 may have anti-fibrotic effect [49].

#### **3.4 ADAMs in polycystic kidney disease (PKD)**

6 Chronic Kidney Disease

High glucose was also shown to promote heparin-binding growth factor (HB-EGF) shedding through ADAM17 activation, however the exact mechanism is unknown [41].

Since ADAM17 activates secretion of TNF, pharmacological inhibitors of the enzyme were tested on blood glucose regulation in animal model of non-obesity-related insulin resistance (fructose-fed rats). ADAM17 inhibitor restored the animals' insulin resistance [42]. In another study, animals heterozygous for ADAM17 (+/-) proved to be relatively protected

A close structural relative of ADAM17, ADAM10 is involved in shedding of RAGE: receptor for advanced glycation end products [44]. Since soluble RAGE can block pathophysiological processes initiated by RAGE, ADAM10 activation may slow down development of diabetes. As of today, we do not have data on the pathophysiological role of ADAMTS enzymes in

In vitro studies modelling mechanisms of transplant rejection showed that the mRNA expression of ADAM17 was upregulated in the kidney and that the protein expression of the enzyme was localized next to TNF receptor II. This suggested that ADAM17 may antagonize the effect of TNF by shedding of its receptor during transplant rejection and therefore higher ADAM17 activity might be beneficial [45]. On the other hand, ADAM17 also co-localized with HB-EGF in experimental ischemia-reperfusion injury which suggested that increased shedding of the growth factor may have contributed to the observed fibrotic injury [46]. Pharmacological inhibitors targeting ADAM17 activity reduced renal tissue injury associated with reperfusion. This confirmed that the increased enzyme activity was a

Another ADAM enzyme, ADAM19 was also implicated in allograft nephropathy however,

Renal fibrosis is a manifestation of several pathological processes. Glomerular fibrosis can be induced by over-activation of the renin-angiotensin system, and the developing fibrosis and inflammation can be successfully attenuated by ADAM17 inhibitors in animal models of the injury [7]. We showed previously that serotonin-induced mesangial cell proliferation, which is an important component of glomerular fibrosis, can be inhibited by knocking down ADAM17 expression and inhibiting the enzyme activity [9]. On the other hand, we also found that ADAM17 can protect glomerular function by decreasing podocyte permeability through inducing re-arrangement of the zonula occludens protein ZO-1 [8]. These data suggest that depending on the cellular context the enzyme can have different effect on the renal function. Nonetheless, inhibitors of ADAM17 decreased infiltration of macrophages both in the glomeruli and in the interstitium in models of kidney fibrosis [7, 46] proving that

There is very few data available on ADAMTS enzymes and renal fibrosis. Unilateral ureteral obstruction in rat induced upregulation of ADAMTS-1 in the tubular epithelial cells. Further,

**3.2 ADAMs in renal transplant dysfunction and ischemia reperfusion injury** 

from high-fat diet-induced obesity and diabetes [43].

cause rather than the consequence of the tissue injury [47].

we do not know any mechanistic details of its actions [48].

targeting ADAM17 can be beneficial for preserving renal function.

**3.3 ADAMs in renal fibrosis** 

diabetes mellitus.

Autosomal-recessive polycystic kidney disease (AR-PKD) is one of the most common genetic disorders of the kidney results in end-stage renal disease. This disease leads to rapid enlargement of the kidney through massive cysts formation. The main pathogenic process in cyst development is the overactivation of the mislocalized EGFR in the cystic apical epithelia (for review see [50]). Excessive shedding of the pro-proliferative growth factor, transforming growth factor (TGF) was also observed. Since secretion of TGFis regulated by ADAM17, therapeutic potential of ADAM17 inhibitors were explored and established in the *bpk* murine model of AR-PKD [51]. In a later study, the role of TGF was not confirmed even if ADAM17 inhibitors were beneficial for attenuating cyst development in AR-PKD [52].
