bims-lypmec 2023-08-27 papers

Issue of 2023‒08‒27
six papers selected by
Satoru Kobayashi, New York Institute of Technology

Autophagy. 2023 Aug 24. 1-3

The CTNS-MTORC1 axis couples lysosomal cystine to epithelial cell fate decisions and is a targetable pathway in cystinosis.

Alessandro Luciani, Olivier Devuyst.

Differentiation and fate decisions are critical for the epithelial cells lining the proximal tubule (PT) of the kidney, but the signals involved remain unknown. Defective cystine mobilization from lysosomes through CTNS (cystinosin, lysosomal cystine transporter), which is mutated in cystinosis, triggers the dedifferentiation and dysfunction of the PT cells, causing kidney disease and severe metabolic complications. Using preclinical models and physiologically relevant cellular systems, along with functional assays and a generative artificial intelligence (AI)-powered engine, we found that cystine storage imparted by CTNS deficiency stimulates Ragulator-RRAG GTPase-dependent recruitment of MTORC1 and its constitutive activation. In turn, this diverts the catabolic trajectories and differentiating states of PT cells toward growth and proliferation, disrupting homeostasis and their specialized functions. Therapeutic MTORC1 inhibition by using low doses of rapamycin corrects lysosome function and differentiation downstream of cystine storage and ameliorates PT dysfunction in preclinical models of cystinosis. These discoveries suggest that cystine may act as a lysosomal fasting signal that tailors MTORC1 signaling to direct fate decisions in the kidney PT epithelium, highlighting novel therapeutic paradigms for cystinosis and other lysosome-related disorders.

Keywords: autophagy; chronic kidney disease; cystinosis; drug repurposing; lysosome; nutrient sensing

DOI: https://doi.org/10.1080/15548627.2023.2250165

Methods Protoc. 2023 Aug 09. pii: 72. [Epub ahead of print]6(4):

Real-Time Monitoring of Lysosomal Membrane Permeabilization Using Acridine Orange.

Ida Eriksson, Linda Vainikka, Hans Lennart Persson, Karin Öllinger.

Loss of lysosomal membrane integrity results in leakage of lysosomal hydrolases to the cytosol which might harm cell function and induce cell death. Destabilization of lysosomes often precede apoptotic or necrotic cell death and occur during both physiological and pathological conditions. The weak base acridine orange readily enters cells and accumulates in the acidic environment of lysosomes. Vital staining with acridine orange is a well-proven technique to observe lysosomal destabilization using fluorescence microscopy and flow cytometry. These analyses are, however, time consuming and only adapted for discrete time points, which make them unsuitable for large-scale approaches. Therefore, we have developed a time-saving, high-throughput microplate reader-based method to follow destabilization of the lysosomal membrane in real-time using acridine orange. This protocol can easily be adopted for patient samples since the number of cells per sample is low and the time for analysis is short.

Keywords: acridine orange; high throughput; lysosomal membrane permeabilization; lysosome

DOI: https://doi.org/10.3390/mps6040072

Life Metab. 2023 Oct;2(5): load027

AMPK promotes lysosomal and mitochondrial biogenesis via folliculin:FNIP1.

Jordana B Freemantle, D Grahame Hardie.

The AMP-activated protein kinase (AMPK) is known to maintain the integrity of cellular mitochondrial networks by (i) promoting fission, (ii) inhibiting fusion, (iii) promoting recycling of damaged components via mitophagy, (iv) enhancing lysosomal biogenesis to support mitophagy, and (v) promoting biogenesis of new mitochondrial components. While the AMPK targets underlying the first three of these effects are known, a recent paper suggests that direct phosphorylation of the folliculin-interacting protein 1 (FNIP1) by AMPK may be involved in the remaining two.

DOI: https://doi.org/10.1093/lifemeta/load027

Nat Rev Mol Cell Biol. 2023 Aug 23.

The molecular basis of nutrient sensing and signalling by mTORC1 in metabolism regulation and disease.

Claire Goul, Roberta Peruzzo, Roberto Zoncu.

The Ser/Thr kinase mechanistic target of rapamycin (mTOR) is a central regulator of cellular metabolism. As part of mTOR complex 1 (mTORC1), mTOR integrates signals such as the levels of nutrients, growth factors, energy sources and oxygen, and triggers responses that either boost anabolism or suppress catabolism. mTORC1 signalling has wide-ranging consequences for the growth and homeostasis of key tissues and organs, and its dysregulated activity promotes cancer, type 2 diabetes, neurodegeneration and other age-related disorders. How mTORC1 integrates numerous upstream cues and translates them into specific downstream responses is an outstanding question with major implications for our understanding of physiology and disease mechanisms. In this Review, we discuss recent structural and functional insights into the molecular architecture of mTORC1 and its lysosomal partners, which have greatly increased our mechanistic understanding of nutrient-dependent mTORC1 regulation. We also discuss the emerging involvement of aberrant nutrient-mTORC1 signalling in multiple diseases.

DOI: https://doi.org/10.1038/s41580-023-00641-8