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kiyohito Totsuka, Murilo F Roggia, Takashi Ueta; Retinal degeneration caused by deficient mitochondrial transcription factor A in murine photoreceptors. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5398.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with mitochondrial diseases sometimes presented with retinitis pigmentosa, while the defects in mitochondrial DNA or functions specifically in photoreceptors has been unclear. Herein, to investigate the effect of mitochondrial defects in murine photoreceptors in vivo, we generated photoreceptor-specific conditional knockout (CKO) mice of mitochondrial transcription factor A (TFAM).
We generated CKO mice of TFAM by crossing TFAMflox/flox mice and Crx-Cre mice, while used TFAMflox/flox littermate mice as control. We examined their retina by immunohistochemical analyses at postnatal day 3 (P3), day 7 (P7), day 13 (P13), and 2 months (2M). Retinal morphology was assessed by Hematoxylin-Eosin staning. Deficient TFAM expression in photoreceptors of CKO mice was examined by immunohistochemistry for TFAM protein. The development and survival of photoreceptors in CKO mice were investigated by immunohistochemistry for retinoic acid receptor-γ (Rxr-γ), rhodopsin, m-opsin and s-opsin. TUNEL assay and immunostaining for cleaved caspase 3 and apoptosis inducing factor (AIF) were used for the evaluation of photoreceptor death in CKO mice.
As we expected, TFAM protein expression was adequately abrogated in only photoreceptors in retinas of CKO mice. We confirmed that the retinas in CKO mice generated the outer nuclear layer (ONL), although thinner than the ONL of the control mice at P7. After P7 photoreceptors of CKO mice degenerated with TUNEL-positive cell death. The apoptosis in photoreceptors were observed with the cleaved caspase 3, but not with the nuclear translocation of AIF, suggesting capase-dependent apoptosis. In regard to photoreceptor differentiation, Rxr-γ-labeled cells were similarly observed in outer neuroblastic layer of both CKO and control mice at P3. At P13 and 2M, while rhodopsin was expressed in the outer segment of photoreceptors, m- and s- opsin protein expression was significantly diminished.
Photoreceptor-specific CKO mice of TFAM presented with retinal degeneration, specifically cone photoreceptor degeneration. The CKO mice could be an in vivo model for the photoreceptor pathologies related to mitochondrial dysfunctions.
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