Expression of leukocyte adhesion molecules in diabetic mouse kidney with P. gingivalis LPS-induced nephropathy
An immunoglobulin superfamily member VCAM-1 binds to the integrins very late antigen-4/α4β7 on lymphocytes and monocytes, and provides leukocyte migration from the blood stream into tissue. The VCAM-1 expression is up-regulated in renal proximal tubules in several renal chronic diseases, and the renal proximal tubule is targeted in the renal infiltration of T cells and monocytes which are rarely found in normal kidneys (24–27). A member of selectin family E-selectin which expresses at the early inflammatory stage binds to sialylated glycoproteins on leukocytes and promotes the leukocyte weak adhesion, rolling on vessel walls. The E-selectin is present on intertubular capillaries in glomerulonephritis but never in renal tubules (28–30). In this study there were no vessels expressing VCAM-1 or E-selectin in diabetic mice, and in healthy mice administered P. gingivalis LPS only in amounts confirmed to have no effect on the health condition in mice in our previous study (Fig. 1,2,6). However, in diabetic mouse kidneys with P. gingivalis LPS-induced nephropathy the expression of VCAM-1 was identified in the renal tubules and glomeruli, and the expression of E-selectin was identified in the renal parenchyma and glomeruli (Fig. 1,2,6). These results suggest that P. gingivalis LPS give rise to the inflammatory conditions in renal intertubular and glomerular capillaries. Since renal proximal tubules express VCAM-1 in renal diseases, it is thought the tubulitis occurrs in P. gingivalis LPS-induced nephropathy (24–27). It has also been reported that the E-selectin is not expressed in tubules but expressed in renal intertubular capillaries in renal diseases, and that soluble E-selectin plays a role to promote glomerulonephritis (28–30). It appears that the immunoreaction of anti-E-selectin in diabetic kidneys with P. gingivalis LPS-induced nephropathy can be ascribed to a soluble E-selectin diffused in renal parenchyma or to E-selectin expression of intertubular capillaries.
Expression of renal physiologically active molecules in diabetic mouse kidneys with P. gingivalis LPS-induced nephropathy
The FGF23 directly targets proximal tubules to increase phosphate excretion by downregulating the cell surface expression of the sodium-dependent phosphate transporters in the proximal tubule. The FGF23 lowers serum phosphorus concentrations by the suppression of phosphorus reabsorption in proximal tubules and by active vitamin D reduction through 1α-hydroxylase suppression (31–33). In this study FGF23 was not detected in diabetic mice or in healthy mice administered P. gingivalis LPS (Fig. 3,6). However, in diabetic mouse kidneys with P. gingivalis LPS-induced nephropathy FGF23 was immunohistochemically detectable in renal tubules and in glomeruli (Fig. 3,6), suggesting that FGF23 accumulates and that excessive phosphate uptake is promoted in inflamed renal tubules of P. gingivalis LPS-induced diabetic nephropathy. It is thought that periodontitis may induce the increase in serum phosphorus concentration by the renal FGF23 accumulation, which contributes to the occurrence of cardiovascular failure in diabetic patients. The ACE2 is locally expressed in the brush border of proximal tubular epithelial cells and the expression amounts increase in diabetic kidneys, and in hypertensive renal diseases. In other organs ACE2 mRNA is expressed in cardiovascular and gastrointestinal tissues, and present at lower levels in many tissues. The ACE2 protein is detectable in blood vessels, upper airways, and lungs, and the expression pattern in humans is similar to that in mice (34, 35). In this study ACE2 were only immunohistochemically detected in the proximal tubular cells and not in other regions including the distal tubules in diabetic mice without the LPS administration, and also not in healthy mice administered P. gingivalis LPS (Fig. 4,6). However, in diabetic mouse kidneys with P. gingivalis LPS-induced nephropathy ACE2 was immunohistochemically detected both in renal tubules as well as in glomeruli (Fig. 4,6), suggesting that renovascular hypertension based on the glomerular ACE2 overexpression may be promoted in inflamed glomeruli of P. gingivalis LPS-induced diabetic nephropathy.
Distribution of macrophages in diabetic mouse kidneys with P. gingivalis LPS-induced nephropathy
Macrophages and T17 express podoplanin, and activate platelet CLEC-2 under inflammatory conditions as well as they aggregate activated platelets. Macrophage antigen-1 (Mac-1) is a heterodimer integrin composed of the αM(CD11b) and β2(CD18) subunits, abundantly expressed on monocyte/macrophages. The Mac-1 is critical for the adhesion and migration into the extracellular matrix (36–39). In this study Mac-1 positive cells were detected in healthy mouse kidneys with P. gingivalis LPS administration (Fig. 5,6) at the same level as in healthy mice without LPS administration (not shown). The number of Mac-1 and podoplanin-positive cells increased in the renal parenchyma with diabetic conditions and accumulated in significant numbers in P. gingivalis LPS-induced diabetic nephropathy (Fig. 5,6). Since the expression of VCAM-1 and E-selectin is significantly upregulated in glomeruli, tubules and intertubular capillaries with P. gingivalis LPS-induced diabetic nephropathy (Fig. 1,2,6), it is thought that the inflammatory infiltration of monocyte-macrophage lineage in the kidney promoted with P. gingivalis LPS under the diabetic condition. Considering that the glomerular ACE2 overexpression and renal FGF23 accumulation promote the renovascular hypertension, it is thought that P. gingivalis LPS progressively accelerates the development of an inflammatory environment in renal proximal tubules, glomeruli, and intertubular capillaries by the LPS recognition via TLR in the diabetic kidneys. Periodontitis may be a critical factor in the progress of nephropathy in diabetic patients.