Mylene Potier

Estrogen-related abnormalities in glomerulosclerosis-prone mice: reduced mesangial cell estrogen receptor expression and prosclerotic response to estrogens.

The development and progression of glomerulosclerosis (GS) is determined by the genetic background. The incidence of end-stage renal disease is increased in postmenopausal women, suggesting that estrogen deficiency may play a role in the accumulation of extracellular matrix by mesangial cells (MCs), which are primarily responsible for the synthesis and degradation of this matrix. Using mouse models that are prone or resistant to the development of GS, we compared the expression of estrogen receptor (ER)-alpha and ER-beta subtypes in GS-prone and GS-resistant glomeruli and isolated MCs, and examined the effects of estrogens on ER, collagen, and matrix metalloproteinase (MMP) expression in MCs. Glomeruli and MCs from GS-prone mice had decreased expression of ER-alpha and ER-beta subtypes and ER transcriptional activity was also decreased in their MCs. Importantly, although 17 beta-estradiol treatment resulted in decreased collagen accumulation and increased MMP-9 expression and activity in MCs from GS-resistant mice, there was, paradoxically, no effect on collagen accumulation and decreased MMP-9 expression and activity in MCs from GS-prone mice. Thus, GS susceptibility is associated with diminished ER expression in MCs. The renal protective effects of estrogens, including decreased collagen accumulation and increased MMP-9 expression, seem to be blunted in GS-prone MCs.

Estrogen Deficiency Accelerates Progression of Glomerulosclerosis in Susceptible Mice

Estrogen deficiency may contribute to the development and progression of glomerulosclerosis in postmenopausal women. The responsiveness to estrogens could be controlled by genetic traits related to those that determine the susceptibility to glomerular scarring. This study was undertaken to determine whether the intensity of the sclerotic response was modified by the estrogen status in sclerosis-prone ROP Os/+ mice. Ovariectomized ROP Os/+ mice developed more severe renal dysfunction and glomerulosclerosis than intact, ie, estrogen sufficient age-matched female mice. Ovariectomized ROP Os/+ exhibited increased accumulation of extracellular matrix, predominantly of laminin, and a marked distortion of the glomerular architecture. We found an increase in macrophage infiltration in the mesangium of ovariectomized ROP Os/+. Estrogen deficiency decreased glomerular estrogen receptor expression in ROP Os/+ mice, which we had previously found to be low in the parental ROP strain. Thus, although physiological estrogen levels in young ROP Os/+ mice could not prevent the development of glomerulosclerosis, estrogen deficiency accelerated the progression of glomerular scarring in this mouse strain. This suggests that estrogen replacement will slow but not prevent the progression of glomerulosclerosis. It underscores the importance of the genetic composition of individuals that determines the susceptibility to diseases as well as the response to treatment.

Resistance to Glomerulosclerosis in B6 Mice Disappears after Menopause

The frequency of chronic renal failure increases with age, especially in women after menopause. Glomerulosclerosis is a common cause of chronic renal failure in aging. We reported that pre-menopausal female C57BL6 (B6) mice are resistant to glomerulosclerosis, irrespective of the type of injury. However, we now show that B6 mice develop progressive glomerulosclerosis after menopause. Glomerular lesions, first recognized in 18-month-old mice, consisted of hypertrophy, vascular pole sclerosis, and mesangial cell proliferation. Diffuse but moderate mesangial sclerosis and more marked hypertrophy were present at 22 months. At 28 to 30 months the glomerulosclerosis was diffuse and increased levels of type I and type IV collagen and transforming growth factor-beta 1 mRNA were present. Urine albumin excretion was significantly increased in 30-month-old mice. Mesangial cells isolated from 28-month-old mice retained their sclerotic phenotype in vitro. Comparison of the effects of uninephrectomy (Nx) in 20-month-old and 2.5-month-old mice revealed a 1.7-fold increase in urine albumin excretion, accelerated glomerulosclerosis, and renal function insufficiency in 20-month-old Nx mice, but not in 2.5-month-old Nx mice. Glycemic levels, glucose, insulin tolerance, and blood pressure were normal at all ages. Thus, B6 mice model the increased frequency of chronic renal failure in postmenopausal women and provide a model for studying the mechanism(s) of glomerulosclerosis in aging women.

The glomerulosclerosis of aging in females: contribution of the proinflammatory mesangial cell phenotype to macrophage infiltration.

Age-associated renal changes may be an important cause of renal failure. We recently found that aged female B6 mice developed progressive glomerular lesions. This was associated with macrophage infiltration, a frequent finding in glomerulosclerosis. We used these mice as a model for studying the mechanisms of glomerular aging. We compared the gene expression profile of intact glomeruli from late postmenopausal (28-month-old) mice to that of intact glomeruli from premenopausal (5-month-old) mice. We found that inflammation-related genes, especially those expressed by activated macrophages, were up-regulated in the glomeruli of 28-month-old mice, a result correlating with the histological observation of glomerular macrophage infiltration. The mechanism for macrophage recruitment could have been stable phenotypic changes in mesangial cells because we found that mesangial cells isolated from 28-month-old mice expressed higher levels of RANTES and VCAM-1 than cells from 5-month-old mice. The elevated serum tumor necrosis factor (TNF)-alpha levels present in aged mice may contribute to increased RANTES and VCAM-1 expression in mesangial cells. Furthermore, cells from 28-month-old mice were more sensitive to TNF-alpha-induced RANTES and VCAM-1 up-regulation. The effect of TNF-alpha on RANTES expression was mediated by TNF receptor 1. Interestingly, mesangial cells isolated from 28-month-old mice had increased nuclear factor-kappaB transcriptional activity. Inhibition of nuclear factor-kappaB activity decreased baseline as well as TNF-alpha-induced RANTES and VCAM-1 expression in mesangial cells isolated from 28-month-old mice. Thus, phenotypic changes in mesangial cells may predispose them to inflammatory stimuli, such as TNF-alpha, which would contribute to glomerular macrophage infiltration and inflammatory lesions in aging.

MATRIX ACCUMULATION IN MESANGIAL CELLS EXPOSED TO CYCLOSPORINE A REQUIRES A PERMISSIVE GENETIC BACKGROUND

Background. Chronic nephrotoxicity is an important adverse effect of cyclosporine A (CsA) therapy. Tubulo-interstitial lesions and arteriolopathy are common histologic findings. Glomerular lesions are also described, but they are of variable severity. The aim of our study is to determine whether CsA has a direct effect on mesangial cells and whether the cellular response depends on the genetic background. Methods. We studied mesangial cells isolated from mice susceptible (ROP/Le-+Es1b/+Es1a, ROP) and resistant to glomerulosclerosis (B6SJLF1, C57). We previously showed that sclerosis-prone and sclerosis-resistant phenotypes are maintained in vitro. We examined whether CsA exposure directly affected extracellular matrix turnover in mesangial cells and whether the response is determined by the genetic background. Extracellular matrix synthesis and degradation were studied by proline incorporation, ELISA, reverse transcription-polymerase chain reaction, zymography, and reverse zymography. We chose a CsA dose that induced neither cytotoxicity nor apoptosis (1 &mgr;g/ml). Results. At the dose of 1 &mgr;g/ml total collagen accumulation was increased in ROP but not in C57 cells. Matrix metalloproteinase (MMP)-2 activity and mRNA levels were selectively decreased in ROP cells. CsA exposure did not affect tissue inhibitors of MMP (TIMP)-1 and -2 activity or TGF-&bgr;1 mRNA expression and protein synthesis in either cell line. Conclusion. CsA increases total collagen accumulation in mesangial cells from sclerosis-prone mice by decreasing MMP-2 activity, but does not affect cells from sclerosis-resistant mice. Thus, CsA directly affects mesangial cells, but only those with a permissive genetic background for glomerulosclerosis.

Glomerular Aging in Females Is a Multi-Stage Reversible Process Mediated by Phenotypic Changes in Progenitors

The glomeruli of postmenopausal C57BL6 mice, and age-matched males, show progressive hypertrophy and glomerulosclerosis. We asked whether this was a multistage process, was due to alterations in glomerular progenitors, and was reversible in female mice. Using cross bone marrow transplants (BMT) between young and old females, we found that BMT delivered a phenotype that was donor age-specific. The fact that lesions in young recipients were more severe if the donors were in late rather than early menopause suggested that new progenitor phenotypes had appeared. Postmenopausal recipients of BMT from young donors had reduced glomerular hypertrophy and sclerosis, implying that the aging lesions in females were reversible and that progenitors, rather than the local environment, determined the glomerular profile. The altered phenotype included increased extracellular matrix synthesis and decreased matrix metalloproteinase-2 levels as well as cell hypertrophy. The mechanism of the cellular hypertrophy was due to uncoupling of hypertrophy from proliferation, resulting from elevated p27 levels. Thus, glomerular hypertrophy and sclerosis in aging females is a multistage process, is reversible, and may be determined by the phenotype of bone marrow-derived progenitor cells.