Surface antigens of human mesangial cells: impact of growth surface or IL-1alpha

Cell biology of mesangial cells: the third cell that maintains the glomerular capillary

The renal glomerulus consists of glomerular endothelial cells, podocytes, and mesangial cells, which cooperate with each other for glomerular filtration. We have produced monoclonal antibodies against glomerular cells in order to identify different types of glomerular cells. Among these antibodies, the E30 clone specifically recognizes the Thy1.1 molecule expressed on mesangial cells. An injection of this antibody into rats resulted in mesangial cell-specific injury within 15 min, and induced mesangial proliferative glomerulonephritis in a reproducible manner. We examined the role of mesangial cells in glomerular function using several experimental tools, including an E30-induced nephritis model, mesangial cell culture, and the deletion of specific genes. Herein, we describe the characterization of E30-induced nephritis, formation of the glomerular capillary network, mesangial matrix turnover, and intercellular signaling between glomerular cells. New molecules that are involved in a wide variety of mesangial cell functions are also introduced.

Thy-1, a versatile modulator of signaling affecting cellular adhesion, proliferation, survival, and cytokine/growth factor responses

Thy-1 is a 25-37 kDa glycosylphosphatidylinositol (GPI)-anchored protein involved in T cell activation, neurite outgrowth, apoptosis, tumor suppression, wound healing, and fibrosis. To mediate these diverse effects, Thy-1 participates in multiple signaling cascades. In this review, we discuss Thy-1 signaling primarily in non-immunologic cell types, including neurons, mesangial cells, ovarian cancer cells, nasopharyngeal carcinoma cells, endothelial cells, and fibroblasts. We review the current literature regarding Thy-1 signaling via integrins, protein tyrosine kinases, and cytokines and growth factors; and the roles of these signaling pathways in cellular adhesion, apoptosis, cell proliferation, and cell adhesion and migration. We also discuss the role of Thy-1 localization to lipid rafts, and of the GPI anchor in Thy-1 signaling. Ongoing research on the mechanisms of Thy-1 signaling will add to our understanding of the diverse physiologic and pathologic processes in which Thy-1 plays a role.

Immunoliposome Targeting to Mesangial Cells: A Promising Strategy for Specific Drug Delivery to the Kidney

Mesangial cell-mediated nephropathies are a frequent cause of ESRD. Specific drug delivery to mesangial cells might be more effective and better tolerated than existing systemic treatments. Rat mesangial cells are characterized by Thy1.1 antigen expression. Therefore, OX7-coupled immunoliposomes (OX7-IL) were prepared by coupling liposomes with F(ab') fragments of OX7 mAb directed against Thy1.1 antigen. As the glomerular endothelium is fenestrated and no basement membrane separates glomerular capillaries from the mesangium, mesangial cells represent a particularly suitable target for drug delivery by OX7-IL. Therefore, the targeting efficacy of OX7-IL to mesangial cells was investigated. Specific targeting in vitro was obtained, and intravenous injection of OX-7-IL to rats showed a specific targeting of all mesangial cells in both kidneys. OX7-IL showed marked accumulation in the cytoplasm of rat mesangial cells, both in vitro and in vivo. This renal targeting was blocked when free OX7 F((ab')2) fragments were co-administered with OX7-IL. Rats that were given a single intravenous injection of low-dose doxorubicin encapsulated in OX7-IL showed extensive glomerular damage, whereas other parts of the kidney and other organs were spared. Free doxorubicin and the liposomal formulation of this agent had no effect. Thus, immunoliposomes are a very promising delivery system for the treatment of kidney diseases.

FTY720 impairs necrosis development after ischemia-reperfusion injury

Ischemia-reperfusion (IR) injury is a common early feature that contributes to graft damage by impairing resident cell function. Our previous results showed that IR injury impaired renal function, by causing extensive tubular necrosis and increasing MHC class II and ICAM-1 molecule expression by mesangial cells (MC). MCs are likely candidates to come into close contact with immune cells such as monocytes or lymphocytes. It has been suggested that under inflammatory circumstances, there is increased MC expression of MHC class II, of adhesion molecules (such as ICAM-1), of cytokines receptors, and of molecules associated with cellular death (apoptosis). The immunosuppressive properties of FTY720 have been shown in clinical and experimental situations. It has also been shown to be protective against IR injury in rats. We sought to evaluate the role of FTY720 in a murine IR model by measuring renal function, tubular necrosis, and surface molecule expression by cultured mesangial cells. Intravenous administration of FTY720 (1 mg/kg) immediately before IR induction did not improve the short-term (24 hours) outcome of renal function or reduced MHC class II and ICAM-1 surface molecule expression. However, there was a decreased percentage of tubular necrosis in mice treated with FTY720 (51.3% +/- 1.6%) compared with vehicle-treated mice (66% +/- 5.5%). These results suggest a protective role of FTY720 in an IR injury model. More studies are required to identify the mechanisms involved in the protective activity of FTY720 in the IR injury model.