Clinical and pathologic features of focal segmental glomerulosclerosis with mitochondrial tRNALeu(UUR) gene mutation

Clinical and pathologic features of focal segmental glomerulosclerosis with mitochondrial tRNALeu(UUR) gene mutation.BackgroundSeveral families have been described in which an A to G transition mutation at position 3243 (A3243G) of the mitochondrial DNA (mtDNA) is associated with focal and segmental glomerulosclerosis (FSGS). However, the prevalence, clinical features, and pathophysiology of FSGS carrying mtDNA mutations are largely undefined.MethodsAmong 11 biopsy-proven primary FSGS patients of unknown etiology, we examined seven FSGS patients to determine whether any of the clinical and pathological features of FSGS were associated with an A3243G mtDNA mutation. In four subjects in whom the A3243G mtDNA mutation was discovered in blood leukocytes, as well as in urine sediments, we retrospectively reviewed the medical records and re-evaluated the renal biopsy specimen using light and electron microscopy. We further screened the patient's family members for the presence and degree of heteroplasmy for this mtDNA mutation and obtained medical histories that were consistent with mitochondrial cytopathy.ResultsThe four individuals identified with the A3243G mtDNA mutation were female. Proteinuria was diagnosed in these individuals during a routine annual health checkup in their teenage years. None of the patients showed any symptoms related to mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode, whereas diabetes mellitus in two of the patients and a hearing disturbance in one patient became manifest within a 3- to 13-year follow-up period. Strict maternal transmitted inheritance was confirmed by pedigree studies in all of these patients. Steroid therapy was ineffective in all four patients. In two of these patients, renal function declined slowly to end-stage renal failure. Histologic examination of biopsy specimens revealed that glomeruli were not hypertrophied, while electron microscopic examination identified severely damaged, multinucleated podocytes containing extremely dysmorphic abnormal mitochondria in all patients.ConclusionsFSGS may belong to the spectrum of renal involvement in A3243G mtDNA mutation in humans. Severely injured podocytic changes containing abnormal mitochondria may explain the pathogenesis of FSGS in association with the A3243G mtDNA mutation

Effects of Lysophosphatidic Acid, a Novel Lipid Mediator, on Cytosolic Ca 2+

Abstract Lysophosphatidic acid (LPA), the smallest and structurally simplest phospholipid, has the potential to modulate cellular signaling in diverse tissues and cell types, including fibroblasts. In the present study, we assessed the effects of LPA on cultured rat glomerular mesangial cells. Quantitative changes of [Ca 2+ ] i in response to LPA were measured in monolayers of mesangial cells loaded with the fluorescent Ca 2+ indicator fura 2. LPA (10 nmol/L to 100 μmol/L) increased [Ca 2+ ] i in a dose-dependent manner and evoked inositol trisphosphate formation. LPA (1 μmol/L to 30 μmol/L) also elicited a marked, albeit transient, contractile response in mesangial cells cultured on collagen gel, as assessed by a decrease in cell surface area (CSA). The contraction persisted for 5 minutes (CSA decreased by 31%), whereupon the mesangial cells gradually relaxed with a consequent increase in CSA. Pretreatment of mesangial cells with isradipine (1 μmol/L), a dihydropyridine-sensitive Ca 2+ channel blocker, completely blocked LPA-induced contraction. Isradipine also decreased resting [Ca 2+ ] i levels as well as the peak and the subsequently sustained [Ca 2+ ] i levels induced by LPA, suggesting that the contractile effects of LPA are dependent on Ca 2+ entry through voltage-gated Ca 2+ channels. Finally, LPA stimulated an increase in both prostaglandin E 2 synthesis and cAMP accumulation, indicating that these mediators may modulate the contractile effects of LPA. Our study is the first demonstration that exogenous LPA induces mesangial cell contraction and suggests that the contraction is mediated by mobilization of intracellular Ca 2+ by activation of the phosphoinositide cascade as well as by promotion of Ca 2+ entry across the plasma membrane