Ricerc@Sapienza

Duchenne muscular dystrophy (DMD) is a lethal X-linked muscular disease caused by
defective expression of the cytoskeletal protein dystrophin (Dp427). Selected autonomic
and central neurons, including retinal neurons, express Dp427 and/or dystrophin shorter
isoforms. Because of this, DMD patients may also experience different forms of cognitive
impairment, neurological and autonomic disorders, and specific visual defects. DMDrelated
damages to the nervous system are established during development, suggesting
a role for all dystrophin isoforms in neural circuit development and differentiation;
however, to date, their function in retinogenesis has never been investigated. In this
large-scale study, we analyzed whether the lack of Dp427 affects late retinogenesis in
the mdx mouse, the most well studied animal model of DMD. Retinal gene expression
and layer maturation, as well as neural cell proliferation, apoptosis, and differentiation,
were evaluated in E18 and/or P0, P5, P10, and adult mice. In mdx mice, expression
of Capn3, Id3 (E18-P5), and Dtnb (P5) genes, encoding proteins involved in different
aspects of retina development and synaptogenesis (e.g., Calpain 3, DNA-binding
protein inhibitor-3, and b-dystrobrevin, respectively), was transiently reduced compared
to age-matched wild type mice. Concomitantly, a difference in the time required for
the retinal ganglion cell layer to reach appropriate thickness was observed (P0–P5).
Immunolabeling for specific cell markers also evidenced a significant dysregulation
in the number of GABAergic amacrine cells (P5–P10), a transient decrease in the
area immunopositive for the Vesicular Glutamate Transporter 1 (VGluT1) during ribbon
synapse maturation (P10) and a reduction in the number of calretininC retinal ganglion
cells (RGCs) (adults). Finally, the number of proliferating retinal progenitor cells (P5–
P10) and apoptotic cells (P10) was reduced. These results support the hypothesis of
a role for Dp427 during late retinogenesis different from those proposed in consolidated neural circuits. In particular, Dp427 may be involved in shaping specific steps of retina
differentiation. Notably, although most of the above described quantitative alterations
recover over time, the number of calretininC RGCs is reduced only in the mature retina.
This suggests that alterations subtler than the timing of retinal maturation may occur, a
hypothesis that demands further in-depth functional studies.