Effects of growth hormone (GH) in the evolution of Dystrophy disease in model B6.Wk-Lama2dy-2J/J

Author(s)

Maria Denise Fernandes Carvalho

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2009-08-07

Examining board members

Mayana Zatz; Paolo Bartolini; Débora Romeo Bertola; Oswaldo Keith Okamoto; Luiz Augusto Corrêa Passos

• Advisor: Mayana Zatz; Oswaldo Keith Okamoto

Abstract

Muscular dystrophies (DM) are characterized by progressive and irrevertible degeneration of the skeleton muscles. Among them, Duchenne Muscular Dystrophy (DMD) consitutes lethal disease linked to chromossome X, distinguished by the absence of dystrophyn in the muscular fibers membrane, affecting one in each 3,000 boys born alive, who, most of them, will be confined to wheel chairs since the age of 6 and with life expectance, without special care, of 25 years. Despite modern diagnosis techniques, there is not an efficient treatment for these diseases. Some works from the 1970´s and 1980´s suggested that the inhibition of the growth hormone (GH) could retard the dystrophy process evolution in DMD patients. Nevertheless since this observation has not been proven scientifically, in the present work, the GH excess and inhibition effects on a murino model of muscular dystrophy, were studied: i) GH (10μg/mouse/day, i.p., for 10 days) was given to mice: a) dystrophic dy/dy (B6.Wk-Lama2dy-2J/J), with phenotype , resulting in the acceleration of the disease symptoms, confirmed by the performance worsening by 17% in the deambulation test (DT), 64% in the sustaining test (S), 28% in the mat test and 55% in the maximum strength test (MST), in relation to dystrophic mice which had not taken GH; only in the inclination resistance test (IRT) there was no significant difference; however, histological cuts of the gastrocnemius muscle of these mice did not show significant alterations, comparing to dystrophic mice which had not taken the drug: as to degeneration and regeneration markers (DRM) in these animals muscles, the GH did not alter Pax7, MyoD. Laminin and Desmin levels, although it increased by 90% the TGFβ-1 levels, an inflammatory cytokine, that induces fibrosis b) in normal mice, the GH, opposite to the results above, increased the performances by 13% in the DT and by 28% in the ST, and slightly, not significantly, in other two tests; histological cuts revealed that the GH increased by 16.5% the transversal section area of these animals muscles, what could explain the results described above; as to the MDR levels, including those of the TGFβ-1, they were similar to the control animals; ii) a new experimental model, resulting from the crossing of GH genetically deficient mice (Ghrthlit) with dystrophic dy/dy (B6.Wk-Lama2dy-2J/J), showing retardation in the disease evolution; the performances of the dystrophic dwarfs, compared to the normal dwarfs, were better than those of the dystrophic compared to normal animals, namely, 14% larger DT, 71% superior in the ST, 18% larger in the MT, 5.5% larger in the IRT and 102% superior in the MST; histological cuts showed that the interstice area in the dystrophic dwarfs muscles was 29% smaller than that of non-dwarfs dystrophic; the TGFβ-1 levels in these animals were the only MDR studied, which were found to be diminished by 36%, compared to those of the non-dwarfs dystrophic; the GH release inhibition by octreotide, somatostatin analogous, also showed a relative improvement or stabilization in the dystrophy evolution, demonstrated by the increase, ater 60 days treatment, of the performances in the muscle functional tests, compared to those of the dystrophic animals, without treatment: it was 12% larger in the DT, while the control dystrophic animals worsened by 32%; they maintained the same performance in the ST, and 43% in the seizing strength test, while the control dystrophic did not improve their performances in these tests. These results suggest a GH pathologic effect, possibly through the TGFβ-1 levels increase. The GH diminishing, consequently, could lead to the retardation in the disease evolution. These experimental studies open promissing perspectives to test the GH effects inhibition in human dystrophic diseases evolution. (AU)