CIB2 regulates mTORC1 signaling and is essential for autophagy and visual function

Age-related macular degeneration (AMD) is a multifactorial neurodegenerative disorder. Although molecular mechanisms remain elusive, deficits in autophagy have been associated with AMD. Here we show that deficiency of calcium and integrin binding protein 2 (CIB2) in mice, leads to age-related pathologies, including sub-retinal pigment epithelium (RPE) deposits, marked accumulation of drusen markers APOE, C3, A beta, and esterified cholesterol, and impaired visual function, which can be rescued using exogenous retinoids. Cib2 mutant mice exhibit reduced lysosomal capacity and autophagic clearance, and increased mTORC1 signaling-a negative regulator of autophagy. We observe concordant molecular deficits in dry-AMD RPE/choroid post-mortem human tissues. Mechanistically, CIB2 negatively regulates mTORC1 by preferentially binding to 'nucleotide empty' or inactive GDP-loaded Rheb. Upregulated mTORC1 signaling has been implicated in lymphangioleiomyomatosis (LAM) cancer. Over-expressing CIB2 in LAM patient-derived fibroblasts downregulates hyperactive mTORC1 signaling. Thus, our findings have significant implications for treatment of AMD and other mTORC1 hyperactivity-associated disorders. Age-related macular degeneration (AMD) has been connected to deficits in autophagy. Here, the authors demonstrate, in mice and dry-AMD patient samples, that calcium and integrin binding protein 2 (CIB2) regulates Rheb-mTORC1 signaling axis, and subsequently autophagy.

Automated summary

The research demonstrates the role of CIB2 in regulating the Rheb-mTORC1 signaling axis and autophagy in AMD. Molecular deficits and pathologies related to AMD were observed in Cib2 mutant mice and dry-AMD patient samples.