bims-lycede 2024-10-27 papers

J Biol Chem. 2024 Oct 19. pii: S0021-9258(24)02413-X. [Epub ahead of print] 107911

Lysosomal activity depends on TRPML1-mediated Ca2+ release coupled to incoming vesicle fusions.

Arindam Bhattacharjee, Hussein Abuammar, Gábor Juhász.

The lysosomal cation channel TRPML1/MCOLN1 facilitates autophagic degradation during amino acid starvation based on studies involving long-term TRMPL1 modulation. Here we show that lysosomal activation (more acidic pH and higher hydrolase activity) depends on incoming vesicle fusions. We identify an immediate, calcium-dependent role of TRPML1 in lysosomal activation through promoting autophagosome-lysosome fusions and lysosome acidification within 10-20 minutes of its pharmacological activation. Lysosomes also become more fusion competent upon TRPML1 activation via increased transport of lysosomal SNARE proteins syntaxin 7 and VAMP7 by SNARE carrier vesicles. We find that incoming vesicle fusion is a prerequisite for lysosomal Ca2+ efflux that leads to acidification and hydrolytic enzyme activation. Physiologically, the first vesicle fusions likely trigger generation of the phospholipid PI(3,5)P2 that activates TRPML1, and allosteric TRPML1 activation in the absence of PI(3,5)P2 restores autophagosome-lysosome fusion and rescues abnormal SNARE sequestration within lysosomes. We thus identify a prompt role of TRPML1-mediated calcium signaling in lysosomal fusions, activation, and SNARE trafficking.

Keywords: SNARE proteins; autophagy; ion channel; lysosomal acidification; membrane fusion

DOI: https://doi.org/10.1016/j.jbc.2024.107911

Traffic. 2024 Oct;25(10): e12957

Fluorescent Reporters, Imaging, and Artificial Intelligence Toolkits to Monitor and Quantify Autophagy, Heterophagy, and Lysosomal Trafficking Fluxes.

Mikhail Rudinskiy, Diego Morone, Maurizio Molinari.

Lysosomal compartments control the clearance of cell-own material (autophagy) or of material that cells endocytose from the external environment (heterophagy) to warrant supply of nutrients, to eliminate macromolecules or parts of organelles present in excess, aged, or containing toxic material. Inherited or sporadic mutations in lysosomal proteins and enzymes may hamper their folding in the endoplasmic reticulum (ER) and their lysosomal transport via the Golgi compartment, resulting in lysosomal dysfunction and storage disorders. Defective cargo delivery to lysosomal compartments is harmful to cells and organs since it causes accumulation of toxic compounds and defective organellar homeostasis. Assessment of resident proteins and cargo fluxes to the lysosomal compartments is crucial for the mechanistic dissection of intracellular transport and catabolic events. It might be combined with high-throughput screenings to identify cellular, chemical, or pharmacological modulators of these events that may find therapeutic use for autophagy-related and lysosomal storage disorders. Here, discuss qualitative, quantitative and chronologic monitoring of autophagic, heterophagic and lysosomal protein trafficking in fixed and live cells, which relies on fluorescent single and tandem reporters used in combination with biochemical, flow cytometry, light and electron microscopy approaches implemented by artificial intelligence-based technology.

Keywords: ER‐phagy; ER‐to‐lysosome‐associated degradation (ERLAD); artificial intelligence; autophagy; autophagy flux; endolysosomes (EL); heterophagy; lysosomal storage disorders (LSD); lysosomes; tandem fluorescent reporters

DOI: https://doi.org/10.1111/tra.12957

Exp Cell Res. 2024 Oct 22. pii: S0014-4827(24)00385-9. [Epub ahead of print]443(1): 114294

Downregulation of heat shock protein 47 caused lysosomal dysfunction leading to excessive chondrocyte apoptosis.

Yawen Shi, Ying He, Yanan Li, Meng Zhang, Yinan Liu, Hui Wang, Zhiran Shen, Xiaoru Zhao, Rui Wang, Tianyou Ma, Pinglin Yang, Jinghong Chen.

Heat shock protein 47 (HSP47) is a collagen-specific chaperone present in several regions of the endoplasmic reticulum and cytoplasm. Elevated HSP47 expression in cells causes various cancers and fibrotic disorders. However, the consequences of HSP47 downregulation leading to chondrocyte death, as well as the underlying pathways, remain largely unclear. This study presents the first experimental evidence of the localization of HSP47 on lysosomes. Additionally, it successfully designed and generated shRNA HSP47 target sequences to suppress the expression of HSP47 in ATDC5 chondrocytes using lentiviral vectors. By employing a chondrocyte model that has undergone stable downregulation of HSP47, we observed that HSP47 downregulation in chondrocytes, disturbs the acidic homeostatic environment of chondrocyte lysosomes, causes hydrolytic enzyme activity dysregulation, impairs the lysosome-mediated autophagy-lysosome pathway, and causes abnormal expression of lysosomal morphology, number, and functional effector proteins. This implies the significance of the presence of HSP47 in maintaining proper lysosomal function. Significantly, the inhibitor CA-074 Me, which can restore the dysfunction of lysosomes, successfully reversed the negative effects of HSP47 on the autophagy-lysosomal pathway and partially reduced the occurrence of excessive cell death in chondrocytes. This suggests that maintaining proper lysosomal function is crucial for preventing HSP47-induced apoptosis in chondrocytes. The existence of HSP47 is crucial for preserving optimal lysosomal function and autophagic flux, while also inhibiting excessive apoptosis in ATDC5 chondrocytes.

Keywords: Apoptosis; Chondrocyte; Heat shock protein 47; Lysosomal dysfunction

DOI: https://doi.org/10.1016/j.yexcr.2024.114294

Protein Cell. 2024 Oct 23. pii: pwae057. [Epub ahead of print]

Stress granules and organelles: Coordinating cellular responses in health and disease.

Ying Liu, Yin Li, Peipei Zhang.

Membrane-bound organelles and membraneless organelles (MLOs) coordinate various biological processes within eukaryotic cells. Among these, stress granules (SGs) are significant cytoplasmic MLOs that form in response to cellular stress, exhibiting liquid-like properties alongside stable substructures. SGs interact with diverse organelles, thereby influencing cellular pathways that are critical in both health and disease contexts. This review discusses the interplay between SGs and organelles and explores the methodologies employed to analyze interactions between SGs and other MLOs. Furthermore, it highlights the pivotal roles SGs play in regulating cellular responses and the pathogenesis of ALS. Gaining insights into these interactions is essential for deciphering the mechanisms underlying both physiological processes and pathological conditions.

Keywords: interplay; membraneless organelle; organelles; stress granules; techniques

DOI: https://doi.org/10.1093/procel/pwae057

Cell Biosci. 2024 Oct 22. 14(1): 130

Golgiphagy: a novel selective autophagy to the fore.

Yifei Chen, Yihui Wu, Xianyan Tian, Genbao Shao, Qiong Lin, Aiqin Sun.

The Golgi apparatus is the central hub of the cellular endocrine pathway and plays a crucial role in processing, transporting, and sorting proteins and lipids. Simultaneously, it is a highly dynamic organelle susceptible to degradation or fragmentation under various physiological or pathological conditions, potentially contributing to the development of numerous human diseases. Autophagy serves as a vital pathway for eukaryotes to manage intracellular and extracellular stress and maintain homeostasis by targeting damaged or redundant organelles for removal. Recent research has revealed that autophagy mechanisms can specifically degrade Golgi components, known as Golgiphagy. This review summarizes recent findings on Golgiphagy while also addressing unanswered questions regarding its mechanisms and regulation, aiming to advance our understanding of the role of Golgiphagy in human disease.

Keywords: Autophagy; Golgi apparatus; Golgi fragmentation; Golgiphagy; Receptor

DOI: https://doi.org/10.1186/s13578-024-01311-8