To assess the histopathological changes in a postmortem sample derived from an eye donor with Macular Telangiectasia Type 2 (MacTel type 2) to gain further insight into the cause of the disease.
Clinicopathological case report
Postmortem tissue was collected from 5 different donors: one MacTel type 2 patient, one healthy control, two type 2 diabetic patients; one with retinopathy and one without retinopathy, and one patient with unilateral Coat’s disease.
Macular pigment distribution in the posterior part of freshly dissected eyes was documented by macro photography. Paraffin sections from both the macular and peripheral regions were assessed using antigen retrieval and immunohistochemistry to study the distribution of cell-specific markers. Blood vessels were visualized with antibodies directed against collagen IV and claudin5, glial cells with antibodies against glial fibrillary acidic protein (GFAP), vimentin, glutamine synthetase (GS) and retinaldehyde binding protein (RLBP1, also known as CRALBP), microglia with an antibody against allograft inflammatory factor 1 (AIF1, also known as Iba1) and photoreceptors with antibodies against rhodopsin and opsin. Using anatomical landmarks the sections were then matched with the macular pigment distribution and a fluorescein angiogram of the patient that was taken before the patient’s death.
MAIN OUTCOME MEASURES
Presence and distribution of macular pigment and cell-specific markers.
Macular pigment was absent in the macula. Furthermore, abnormally dilated capillaries were identified in a macular region that correlated spatially with regions of fluorescein leakage in an angiogram that was taken 12 years prior to death. These telangiectatic vessels displayed a marked reduction of the basement membrane component collagen IV, indicating vascular pathology. GFAP was limited to retinal astrocytes and no reactive Müller cells were identified. Importantly, reduced immunoreactivity with Müller cell markers (vimentin, GS and RLBP1) in the macula was observed. The area that lacked Müller cells corresponded with the region of depleted macular pigment.
These findings suggest that macular Müller cell loss or dysfunction is a critical component of MacTel type 2, which may have implications for future treatment strategies.