**5. Role of ECM molecules on urinary system**

### **5.1. Upper urinary system**

In the renal cortex, the ECM is present in anatomically distinct areas with different functions depending on its molecular components. Glomerular basal membrane, which is thicker, compared to most other basal membranes in the body mainly contains laminin, collagen type IV, nidogen and heparan sulfate proteoglycans [14].

Laminins in glomerular basal membrane form a network required to maintain the basement membrane integrity. A genetic defect in laminin β2 chain will result in Pierson syndrome, which is characterized by congenital nephrotic syndrome and diffuse mesangial sclerosis, muscular hypotonia, distinct ocular abnormalities like microcoria (small pupils) and impair‐ ment of vision and neurodevelopment [15]. Leading cause of death, which occurs within first days, or weeks of life in Pierson syndrome is renal failure.

Nidogens bind to collagen type IV and laminin separately. Nidogens have a role in the basement membrane formation but experimental evidence on animal studies showed that they are not essentially required for GBM formation [16]. The most common type of heparan sulfate found in healthy basal membrane is agrin [4].

In normal physiologic conditions, ECM of glomerular mesangium consists of fibronectin, collagen type IV, collagen type V, laminin, chondroitin sulfate, heparan sulfate and nidogen [7, 17]. Mesangial ECM allows larger molecules to pass to the mesangium in contrast to glomerular basal membrane. The small proteoglycans like decorin, biglycan, fibromodulin and lumican are most commonly localized in the tubular interstitium and they are also weakly expressed in mesangium [7].

endothelial elements) and the evolving cellular and protein microenvironment [1]. There is a constant turnover of ECM in the body and it is being regulated with either enzymatically or

Matrix metalloproteinases (MMPs) are a large family of endopeptidases, which are calciumdependent zinc-containing enzymes. They are responsible for the degradation of the ECM in which they assist the tissue remodeling and they play a central role in tissue homeostasis [8]. They are present in both pathologic and normal tissues performing proteolytic action [9]. The main cell types excreting MMPs are macrophages, fibroblasts, osteoblasts, endothelial cells,

MMPs have been studied in many conditions. It has been found that they have an impact on tumor cell behavior as a result of their ability to make alterations on cell surface receptors, growth factors, cell adhesion molecules and cytokines. Furthermore, MMPs are able to produce apoptosis-resistant cells, which leads to generation of an aggressive phenotype. MMPs may also regulate angiogenesis positively or negatively in cancer depending on activation of

In bladder cancer, it has been shown that there is a correlation with the levels of MMP-2 and MMP-9 and tumor grade and invasiveness [11]. MMP-2 levels were also found to be strongly associated with tumor stage and prognosis [12]. In a study, serum level of MMP-7 was also found to be associated with the prognosis of the patient. It is reported that in bladder cancer patients treated with radical surgery high MMP-7 plasma levels were significantly associated

In the renal cortex, the ECM is present in anatomically distinct areas with different functions depending on its molecular components. Glomerular basal membrane, which is thicker, compared to most other basal membranes in the body mainly contains laminin, collagen type

Laminins in glomerular basal membrane form a network required to maintain the basement membrane integrity. A genetic defect in laminin β2 chain will result in Pierson syndrome, which is characterized by congenital nephrotic syndrome and diffuse mesangial sclerosis, muscular hypotonia, distinct ocular abnormalities like microcoria (small pupils) and impair‐ ment of vision and neurodevelopment [15]. Leading cause of death, which occurs within first

Nidogens bind to collagen type IV and laminin separately. Nidogens have a role in the basement membrane formation but experimental evidence on animal studies showed that they are not essentially required for GBM formation [16]. The most common type of heparan sulfate

proangiogenic factors or generation of angiogenesis inhibitors, respectively [10].

nonenzymatically which makes ECM a dynamic structure.

226 Composition and Function of the Extracellular Matrix in the Human Body

with poor overall- and disease-specific survival [13].

**5. Role of ECM molecules on urinary system**

IV, nidogen and heparan sulfate proteoglycans [14].

days, or weeks of life in Pierson syndrome is renal failure.

found in healthy basal membrane is agrin [4].

neutrophils and lymphocytes [8].

**5.1. Upper urinary system**

Normally, the renal tubulointerstitial matrix is composed of collagen types I, III, V, VI, VII and XV, both sulfated and nonsulfated GAGs, glycoproteins and polysaccharides. During fibrosis, decreased degradation and increased synthesis of ECM components result in accumulation of these components leading to the formation of scar tissue in the interstitial space [14, 18].

Increasing evidence suggest that MMPs have a complex role in renal fibrosis [19]. For example, MMP-9 mediates collagen degradation. As a result, collagen fragments were formed, and these fragments mediate neutrophil chemotaxis. Including their action on ECM components, it is also shown that MMPs have functional effect on the modulation of growth factors, their receptors and adhesion molecules [19].

In diabetic nephropathy, glomerular hypertension and hyperfiltration lead to mechanical stress on glomerular cells, resulting increased transcription of transforming growth factor (TGF)-β1 and decreased MMP activity. As a result, in diabetic nephropathy, changes seen on glomerular basal membrane increase in the concentration of laminin, fibronectin, collagen IV and VI; increase in glycation of collagen IV, increase in crosslinking of collagen IV and decrease in the concentration of agrin, perlecan and collagen XVIII [18]. Stokes et al. showed an increase in decorin, collagen type 1 and biglycan levels on mesengial matrix in renal fibrosing disease [20]. Collagen type 4 reported to increase both type 1 and type 2 DM associated with the degree of decline in renal function [14].

There are some conditions in which defects on ECM components affect upper urinary tract. Mutations on the α5 chain of collagen type IV result in Alport's syndrome. Genetic defects on the α3 and α4 chains of collagen type 4 can cause autosomal dominant or recessive Alport's syndrome and thin basement membrane nephropathy. Goodpasture syndrome and Alport posttransplantation disease are two autoimmune conditions in which autoantibodies attacking glomerular basal membrane cause rapidly progressive glomerulonephritis.

Thrombospondin-1 (TSP-1) is a glycoprotein, which has adhesive properties, and it is involved in fibroblast proliferation and migration. TSP-1 is correlated with the degree of tubulointer‐ stitial fibrosis. It is also shown that TSP-1 is transiently expressed at early stages of fibrosis. It is suggested that by the activation of TGF-β, TSP-1 could have a possible role as a mediator of interstitial fibrosis [14].

Matrix molecules such as heparan sulfate, proteoglycans, laminins, integrins and MMPs along with a group of growth factors (e.g., TGF-β) are involved in stimulation or inhibition of growth and branching of the ureteral bud [21]. The important role of ECM components and MMPs on the development of ureters puts these molecules on the scope of most recent studies investi‐ gating pathophysiology of congenital ureter-related abnormalities. It is suggested that an increase in ECM components such as collagen 1 may result in ureter-related disorders such as ureteropelvic junction (UPJ) obstruction and ureterovesical junction (UVJ) obstruction [9, 22– 24].

#### **5.2. Bladder and lower urinary system**

The bladder ECM consists of proteins, proteoglycans and GAGs. ECM in bladder provides support and signaling to the cells of the bladder [25]. ECM components have an important role in the protection of urothelium and the storage of urine. The protective layer of GAGs (predominantly chondroitin and heparan sulfates) that cover urothelial cells forms a barrier against various toxic components [25].

Bladder lamina propria forms a highly effective barrier between epithelial and mesenchymal layers. It consists of mainly connective tissue and it also contains myofibroblasts, nerve fibers, lymphatics and blood vessels [26, 27].

Detrusor muscle is associated with laminin, osteopontin and collagen fibrils (I and III) During physiologic bladder filling and emptying, keratoepithelin is organized in complex folds and facilitates expansion and compaction of the bladder. Further, the ECM composition of the bladder wall, and in particular the type of collagen (type I favored in normally compliant bladders), as well as the collagen-to-elastin ratio, are critical to the maintenance of a lowpressure state in the bladder during normal filling [21].

Studies on bladder cancer show that changes in ECM play a crucial role in the course of the disease. It has been shown that bladder cancer cells cultured in a normal ECM lose their invasiveness or ability to form papillary structures. Instead, they align in either multi- or singlelayered formation resembling normal urothelium [28].

Altered distribution of laminin-5 γ2-chain is found to be associated with worse overall survival, higher risk of recurrence and progression; and it is regarded as independent prog‐ nostic factor in bladder cancer treated with TUR-B. Studies demonstrated that loss of collagen IV was associated with invasive behavior and worse overall survival [29].

Fibronectin is found at increased levels in lamina propria and in urine in urothelial carcinoma. Increased expression of it is also found to be associated with stage of the cancer but has no prognostic value. Increased value of fibronectin in urine suggested to be used for early detection of the tumor whereas decreased fibronectin level in the urine can be used to assess response to Bacillus Calmette Guérin (BCG) therapy [29].

Increased stromal expression of tenascin C is found to be associated with worse overall survival in bladder cancer; on the contrary tumor cell expression of tenascin C is associated with improved overall survival [29]. It is also found that in patients with decreased expression levels of TSP-1, high rate of recurrence and worse overall survival is seen [29].

In the function and diseases of prostate the noncellular stroma and ECM of the organ play an important role. Prostate basement membrane contains type IV and V collagen meshwork that is laminin rich and supports basal cells, stem cells, transit-amplifying cells and secretory epithelium.
