tuberous sclerosis: hydroxyproline content in urine and tissues

Drug Inhibition of Redox Factor-1 Restores Hypoxia-Driven Changes in Tuberous Sclerosis Complex 2 Deficient Cells

Therapies with the mechanistic target of rapamycin complex 1 (mTORC1) inhibitors are not fully curative for tuberous sclerosis complex (TSC) patients. Here, we propose that some mTORC1-independent disease facets of TSC involve signaling through redox factor-1 (Ref-1). Ref-1 possesses a redox signaling activity that stimulates the transcriptional activity of STAT3, NF-kB, and HIF-1α, which are involved in inflammation, proliferation, angiogenesis, and hypoxia, respectively. Here, we demonstrate that redox signaling through Ref-1 contributes to metabolic transformation and tumor growth in TSC cell model systems. In TSC2-deficient cells, the clinically viable Ref-1 inhibitor APX3330 was effective at blocking the hyperactivity of STAT3, NF-kB, and HIF-1α. While Ref-1 inhibitors do not inhibit mTORC1, they potently block cell invasion and vasculature mimicry. Of interest, we show that cell invasion and vasculature mimicry linked to Ref-1 redox signaling are not blocked by mTORC1 inhibitors. Metabolic profiling revealed that Ref-1 inhibitors alter metabolites associated with the glutathione antioxidant pathway as well as metabolites that are heavily dysregulated in TSC2-deficient cells involved in redox homeostasis. Therefore, this work presents Ref-1 and associated redox-regulated transcription factors such as STAT3, NF-kB, and HIF-1α as potential therapeutic targets to treat TSC, where targeting these components would likely have additional benefits compared to using mTORC1 inhibitors alone.

Tuberous sclerosis: aberrant proline sensitivity of skin fibroblasts

Cultured skin fibroblasts from patients with tuberous sclerosis were analyzed as to their sensitivities to proline, glutamic acid and arginine, and their analogues by means of a cell growth study. A difference was observed between tuberous sclerosis and normal cells when proline was added. Skin fibroblasts derived from normal-appearing skin of tuberous sclerosis patients exhibited sensitivity to proline. Skin fibroblasts derived from tumorous skin of tuberous sclerosis patients exhibited resistance to proline in the cell growth study and was found to be rather sensitive to proline in a colony formation study. This aberrant sensitivity to proline of tuberous sclerosis cells may indicate abnormal proline metabolism in tuberous sclerosis patients.

Tuberous sclerosis: aberrant metabolism of ornithine, proline and glutamate in cultured fibroblasts

To investigate aberrant metabolism of proline (Pro) and its precursors in tuberous sclerosis (TS), 6, 7 and 5 strains of control, TS (normal skin) and TS (tumor) fibroblasts, respectively, were cultured in Eagle's MEM containing dialyzed fetal bovine serum with or without 0.1 mM ornithine (Orn). Ornithine aminotransferase (OAT) activity was decreased in TS, especially in TS (tumor) after mild sonication treatment. The yield of the OAT protein was inhibited in TS (tumor) when cultured without Orn. Free glutamate (Glu) in the medium was significantly increased in TS (tumor). Free proline (Pro) in cells was significantly decreased in TS (tumor) when cultured with Orn, but protein-bound Pro was not. The relative concentration of free Glu to glutamine (Gln) in the medium and that of free Glu to Pro in cells cultured with Orn were increased in TS (tumor). These results suggest that the requirement for Orn, increased turnover of Pro to Glu and increased elimination of Glu into the medium occur in TS (tumor). Aberrant regulation or turnover of Pro and Glu metabolism may occur in TS, especially in tumor cells.

Rapid rejoining of X-ray-induced DNA single-strand breaks in tuberous sclerosis fibroblasts

The formation and rejoining rates of X-ray-induced DNA single-strand breaks (SSBs) were examined in radiosensitive and non-radiosensitive fibroblast lines from patients with tuberous sclerosis (TS), and fibroblasts from normal individuals, using the sensitive and quantitative alkaline elution method. No difference was found between these cell lines in the frequency of DNA SSBs directly produced by X-irradiation at any dose up to 750 rad. Kinetic analysis of the rate of rejoining of DNA SSBs after X-irradiation at 500 rad indicated that the rate of rejoining involved at least two components, an initial fast component and a slower component. TS fibroblast lines, either radiosensitive or nonsensitive, were proficient as to DNA SSB repair, but they showed an increased rate of rejoining in the initial fast repair process, when compared to normal fibroblast lines. Although the molecular basis for the accelerated rejoining of DNA SSBs remains unknown, it is possible that the abnormality may be related to a basic defect in TS.

Tuberous sclerosis: proline and hydroxyproline contents in serum

The serum levels of proline and hydroxyproline were determined by high-performance liquid chromatography using the post-labeled method with o-phthalaldehyde and sodium hypochlorite in 30 patients of tuberous sclerosis (TS) and compared with those in 32 pathological control subjects of similar age. No significant difference in the levels of serum free hydroxyproline was observed between TS and controls in any age group. In the age group of 9 to 18 years, TS showed significantly higher mean free proline levels in serum than controls with a difference of about 50 mumol/L. In both groups of TS and controls, total and free levels of hydroxyproline from ethanol-extractable serum showed similar age-dependent curves with peak values at age 12 years, and there was also no difference in the 2 levels between the 2 groups. It is suggested that this higher free proline level in TS with the autosomal dominant trait may be explained as the abnormal regulation of proline metabolism.

Immunohistochemical and biochemical studies on collagen types in angiofibromas and shagreen patches from patients with tuberous sclerosis

The distribution of collagen types in angiofibroma and shagreen patch from patients with tuberous sclerosis was examined biochemically and immunohistochemically by indirect immunofluorescence microscopy using type-specific anti-collagen antibodies. Types I and III collagens were distributed in the interstitium of whole tumor tissues of angiofibriomas and a shagreen patch, showing relatively fine fibers at the periphery and large bundles in the center. No significant difference in the distribution of type I and III collagens was observed. Densitometric analysis of gel electrophoresis patterns of collagens solubilized from the skin by limited pepsin digestion revealed that both type I and III collagens were the main constituents of the diseased regions of the skin with tuberous sclerosis, and the ratio of type I collagen/type III collagen was relatively constant, which was not contradictory to the results of immunofluorescence microscopy. The presence of an unidentified component, probably type V collagen, was observed in the angiofibroma tissue from one patient with tuberous sclerosis.