High Glucose Level Unmasks a Genetic Predisposition to Enhanced Extracellular Matrix Production in Mesangial Cells from the Milan Normotensive Strain GIUSEPPE PUGLIESE,* FLAVIA PRICCI,* PAOLO MENE,* GIULIO ROMEO,* ITALO NOFRONI,* STEFANO GIANNINI,t BARBARA CRESCI,t GIANNA GALLI,t CARLO M. ROTELLA,t UMBERTO DI MARIO, and FRANCESCO PUGLIESE* *Dipartimento di Medicina Sperimenta!e (Pato!ogia Generale 1e Statistica Medica e Biometria) and Clinica Medica II (Endocrinologia I and Nefro!ogia), University of Rome “La Sapienza, “ Rome, Italy; Dipartimento di Fisiopatologia Clinica (Endocrino!ogia) and Clinica Medica III, University of Florence, Florence, Italy; Dipartimento di Medicina Sperimentale e Clinica (Endocrinologia), University of Reggio Calabria, Catanzaro, Italy. Abstract. A growing body of evidence indicates that the mdi- vidual genetic background plays a role in the pathogenesis of diabetic gbomerular disease by either favoring or protecting against injury produced by hyperglycemia. Two genetically related rat strains, the Milan normotensive strain (MNS) and the Milan hypertensive strain (MHS) display different suscep- tibilities to develop glomerubosclerosis with age. Gbomerubar scberosing lesions occur in the MNS rats, which remain nor- motensive throughout their entire life-span, but not in the MHS rats, despite the presence of arterial hypertension. Previous studies have reported that extracellular matrix production and cell proliferation increased with donor-aging in mesangial cells isolated from MNS rats, but not in those from MHS rats, thus suggesting the existence of an inherited defect in the regulation of cell and matrix turnover, which translates into an abnormal response to growth-promoting stimuli favoring the develop- ment of gbomerubosclerosis. In the study presented here, it was hypothesized that, in addition to donor-aging, other indepen- dent risk factors for the development of glomerular disease, such as metabolic injury by hyperglycemia, would be able to trigger and/or precipitate the occurrence of these changes in mesangial cells from the susceptible normotensive strain, but not in those from the protected hypertensive strain. To test this hypothesis, mesangial cells obtained from these rat strains (before the onset of either gbomerulosclerosis or hypertension) were used to assess the effects of prolonged (4 wk) exposure to high (30 mmollL) versus normal (5.5 mmol/L) glucose con- centrations on extracellubar matrix and cytokine production and cell proliferation. The accumulation and/or gene expression of the matrix components fibronectin, laminin, and collagen IV, and of the cytokines insulin-like growth factor-I (IGF-I) and transforming growth factor-n (TGF-f3) did not change under normal glucose and increased progressively in response to high glucose in both MNS and MHS cells. These increases, with the exception of the increment in TGF- gene expression, were significantly more pronounced in MNS cells than in MHS cells. In contrast, the proliferative response to serum was not affected by high glucose, but increased in MNS cells, and decreased, although not significantly, in MHS cells during the 4-wk period, thus mimicking the changes previously observed in these rat strains as a function of age. These results indicate that high glucose unmasks a genetic tendency to produce increasing amounts of extracelbular matrix, not yet evident under normal glucose conditions, and suggest that a genetically determined propensity of mesangial cells to hyperrespond to chronic hyperglycemia may be implicated in the pathogenesis ofdiabetic glomerular disease. (J Am Soc Nephrol 8: 406-414, 1997) Kidney disease of diabetes mebbitus (KDDM), like other forms of glomerular disease, is characterized by an expansion of the mesangial region, which appears to be of central importance in the progression toward gbomerubosclerosis (OS) (1 ,2). Mesan- gial expansion is rebated predominantly to an enhanced accu- Received June 7, 1996. Accepted September 3, 1996. Correspondence to Dr. Francesco Pugliese, Clinica Medica II, Division of Nephrobogy, “La Sapienza” University of Rome, Policlinico Umberto I, Viale del Policlinico, 1-00161 Rome, Italy. l046-6673/0803-0406$03.00/0 Journal of the American Society of Nephrology Copyright © 1997 by the American Society of Nephrology mubation of extraceblular matrix (ECM) (1,2), possibly pre- ceded and/or accompanied by increased cellularity (3). Several experimental observations have indicated that hy- perglycemia plays a pivotal role in triggering the cascade of events beading to KDDM by modulating the increased ECM accumulation underlying mesangial expansion (4-6), possibly via an enhanced production of cytokines such as transforming growth factor-f3 (TGF-) and insulin-like growth factor-I (IGF-I) (7-10). The primary role of hyperglycemia in initiating and possibly sustaining the diabetic gbomerular scberosing process is sug- gested by clinical and epidemiologicab studies showing that diabetic complications are related to the degree and duration of