This paper tells the same thing and I hope that Kempler knows it also :

J Biol Chem. 2017 Aug 4;292(31):12895-12905. doi: 10.1074/jbc.M117.788422. Epub 2017 Jun 14.

Human retinal pigment epithelial cells prefer proline as a nutrient and transport metabolic intermediates to the retinal side.

Chao JR¹, Knight K², Engel AL², Jankowski C³, Wang Y^4,5, Manson MA², Gu H⁶, Djukovic D⁶, Raftery D⁶, Hurley JB^2,3, Du J^7,5.

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Abstract

Metabolite transport is a major function of the retinal pigment epithelium (RPE) to support the neural retina. RPE dysfunction plays a significant role in retinal degenerative diseases. We have used mass spectrometry with ¹³C tracers to systematically study nutrient consumption and metabolite transport in cultured human fetal RPE. LC/MS-MS detected 120 metabolites in the medium from either the apical or basal side. Surprisingly, more proline is consumed than any other nutrient, including glucose, taurine, lipids, vitamins, or other amino acids. Besides being oxidized through the Krebs cycle, proline is used to make citrate via reductive carboxylation. Citrate, made either from ¹³C proline or from ¹³C glucose, is preferentially exported to the apical side and is taken up by the retina. In conclusion, RPE cells consume multiple nutrients, including glucose and taurine, but prefer proline, and they actively synthesize and export metabolic intermediates to the apical side to nourish the outer retina.