Subcellular distribution and activity of mechanistic target of rapamycin in aged retinal pigment epithelium

Area of Science:

• Cell Biology
• Aging Research
• Ophthalmology

Background:

• Mechanistic target of rapamycin (mTOR) signaling regulates cell growth and metabolism, and its inhibition extends lifespan in mammals.
• mTOR activity is influenced by upstream regulators and its location within the cell.
• The retinal pigment epithelium (RPE) is crucial for vision and is composed of postmitotic cells susceptible to aging-related changes.

Purpose of the Study:

• To investigate age-related changes in mTOR signaling within RPE cells.
• To understand the functional consequences of these age-related alterations in RPE.
• To characterize the impact of mTOR on the degradation of phagocytosed photoreceptor outer segments (POS).

Main Methods:

• Assessed mTOR complex 1 (mTORC1) activity by measuring S6 protein phosphorylation in cultured human RPE and aged mouse RPE explants.
• Determined mTOR subcellular localization using immunofluorescent staining in RPE.
• Modulated mTORC1 signaling via Rheb overexpression or Ragulator complex disruption and measured rhodopsin turnover to assess POS degradation.

Main Results:

• Aged RPE cells exhibited increased lysosome-associated mTOR and heightened response to amino acid stimulation.
• Disruption of the Ragulator complex impaired amino acid-induced mTORC1 activation, highlighting the importance of lysosome distribution.
• Elevated mTORC1 activity in aged RPE cells led to a reduced rate of POS degradation.

Conclusions:

• Aging alters the subcellular localization and function of mTOR in RPE cells.
• Increased mTORC1 activity in aged RPE impairs the degradation of POS.
• This dysfunction may exacerbate age-related lysosome problems in the RPE, potentially impacting vision.