Loss of Class III Phosphoinositide 3-Kinase Vps34 Results in Cone Degeneration

Regulatory Mechanisms Governing the Autophagy-Initiating VPS34 Complex and Its inhibitors

VPS34 is a crucial protein in cells, essential for handling cellular stress through its involvement in autophagy and endocytosis. This protein functions as a Class III phosphatidylinositol 3-kinase, producing phosphatidylinositol 3-phosphate, which is necessary for autophagy and vesicle trafficking. Additionally, VPS34 forms two mutually exclusive complexes, each playing a vital role in autophagy and endocytic sorting. These complexes share common subunits, including VPS15, VPS34, and Beclin 1, with complex I having ATG14 as a specific subunit. Due to its association with various human diseases, regulation of the VPS34 complex I has garnered significant interest, emerging as a potential therapeutic target for drug discovery. Summaries of the structure, function of VPS34 complexes, and developed VPS34 inhibitors have been provided, along with discussions on the regulation mechanism of VPS34, particularly in relation to the initiation complex I of autophagy. This offers valuable insights for treating autophagy-related diseases.

Mitophagy in the retina: Viewing mitochondrial homeostasis through a new lens

Mitochondrial function is key to support metabolism and homeostasis in the retina, an organ that has one of the highest metabolic rates body-wide and is constantly exposed to photooxidative damage and external stressors. Mitophagy is the selective autophagic degradation of mitochondria within lysosomes, and can be triggered by distinct stimuli such as mitochondrial damage or hypoxia. Here, we review the importance of mitophagy in retinal physiology and pathology. In the developing retina, mitophagy is essential for metabolic reprogramming and differentiation of retina ganglion cells (RGCs). In basal conditions, mitophagy acts as a quality control mechanism, maintaining a healthy mitochondrial pool to meet cellular demands. We summarize the different autophagy- and mitophagy-deficient mouse models described in the literature, and discuss the potential role of mitophagy dysregulation in retinal diseases such as glaucoma, diabetic retinopathy, retinitis pigmentosa, and age-related macular degeneration. Finally, we provide an overview of methods used to monitor mitophagy in vitro, ex vivo, and in vivo. This review highlights the important role of mitophagy in sustaining visual function, and its potential as a putative therapeutic target for retinal and other diseases.

Targeting VPS34 in autophagy: An update on pharmacological small-molecule compounds

VPS34 is well-known to be the unique member of the class III phosphoinositide 3-kinase (PI3K) family, forming VPS34 complex 1 and complex 2, which are involved in several key physiological processes. Of note, VPS34 complex 1 is an important node of autophagosome generation, which controls T cell metabolism and maintains cellular homeostasis through the autophagic pathway. And, VPS34 complex 2 is involved in endocytosis as well as vesicular transport, and is closely related to neurotransmission, antigen presentation and brain development. Due to the two important biological functions of VPS34, its dysregulation can lead to the development of cardiovascular disease, cancer, neurological disorders, and many types of human diseases by altering normal human physiology. Thus, in this review, we not only summarize the molecular structure and function of VPS34, but demonstrate the relationships between VPS34 and human diseases. Moreover, we further discuss the current small molecule inhibitors targeting VPS34 based upon the structure and function of VPS34, which may provide an insight into the future targeted drug development.

Atlas of phosphoinositide signatures in the retina identifies heterogeneity between cell types

Phosphoinositides (PIPs) are a family of minor acidic phospholipids in the cell membrane. Phosphoinositide (PI) kinases and phosphatases can rapidly convert one PIP product into another resulting in the generation of seven distinct PIPs. The retina is a heterogeneous tissue composed of several cell types. In the mammalian genome, around 50 genes encode PI kinases and PI phosphatases; however, there are no studies describing the distribution of these enzymes in the various retinal cell types. Using translating ribosome affinity purification, we have identified the in vivo distribution of PI-converting enzymes from the rod, cone, retinal pigment epithelium (RPE), Müller glia, and retinal ganglion cells, generating a physiological atlas for PI-converting enzyme expression in the retina. The retinal neurons, rods, cones, and RGCs, are characterized by the enrichment of PI-converting enzymes, whereas the Müller glia and RPE are characterized by the depletion of these enzymes. We also found distinct differences between the expression of PI kinases and PI phosphatases in each retinal cell type. Since mutations in PI-converting enzymes are linked to human diseases including retinal diseases, the results of this study will provide a guide for what cell types are likely to be affected by retinal degenerative diseases brought on by changes in PI metabolism.

Targeting Class I-II-III PI3Ks in Cancer Therapy: Recent Advances in Tumor Biology and Preclinical Research

Phosphatidylinositol-3-kinase (PI3K) enzymes, producing signaling phosphoinositides at plasma and intracellular membranes, are key in intracellular signaling and vesicular trafficking pathways. PI3K is a family of eight enzymes divided into three classes with various functions in physiology and largely deregulated in cancer. Here, we will review the recent evidence obtained during the last 5 years on the roles of PI3K class I, II and III isoforms in tumor biology and on the anti-tumoral action of PI3K inhibitors in preclinical cancer models. The dependency of tumors to PI3K isoforms is dictated by both genetics and context (e.g., the microenvironment). The understanding of class II/III isoforms in cancer development and progression remains scarce. Nonetheless, the limited available data are consistent and reveal that there is an interdependency between the pathways controlled by all PI3K class members in their role to promote cancer cell proliferation, survival, growth, migration and metabolism. It is unknown whether this feature contributes to partial treatment failure with isoform-selective PI3K inhibitors. Hence, a better understanding of class II/III functions to efficiently inhibit their positive and negative interactions with class I PI3Ks is needed. This research will provide the proof-of-concept to develop combination treatment strategies targeting several PI3K isoforms simultaneously.

New insights into the role of autophagy in retinal and eye diseases

Autophagy is a fundamental homeostatic pathway that mediates the degradation and recycling of intracellular components. It serves as a key quality control mechanism, especially in non-dividing cells such as neurons. Proteins, lipids, and even whole organelles are engulfed in autophagosomes and delivered to the lysosome for elimination. The retina is a light-sensitive tissue located in the back of the eye that detects and processes visual images. Vision is a highly demanding process, making the eye one of the most metabolically active tissues in the body and photoreceptors display glycolytic metabolism, even in the presence of oxygen. The retina and eye are also exposed to other stressors that can impair their function, including genetic mutations and age-associated changes. Autophagy, among other pathways, is therefore a key process for the preservation of retinal homeostasis. Here, we review the roles of both canonical and non-canonical autophagy in normal retinal function. We discuss the most recent studies investigating the participation of autophagy in eye diseases such as age-related macular degeneration, glaucoma, and diabetic retinopathy and its role protecting photoreceptors in several forms of retinal degeneration. Finally, we consider the therapeutic potential of strategies that target autophagy pathways to treat prevalent retinal and eye diseases.

Regulation of Phosphoinositide Levels in the Retina by Protein Tyrosine Phosphatase 1B and Growth Factor Receptor-Bound Protein 14

Protein tyrosine kinases and protein phosphatases play a critical role in cellular regulation. The length of a cellular response depends on the interplay between activating protein kinases and deactivating protein phosphatases. Protein tyrosine phosphatase 1B (PTP1B) and growth factor receptor-bound protein 14 (Grb14) are negative regulators of receptor tyrosine kinases. However, in the retina, we have previously shown that PTP1B inactivates insulin receptor signaling, whereas phosphorylated Grb14 inhibits PTP1B activity. In silico docking of phosphorylated Grb14 and PTP1B indicate critical residues in PTP1B that may mediate the interaction. Phosphoinositides (PIPs) are acidic lipids and minor constituents in the cell that play an important role in cellular processes. Their levels are regulated by growth factor signaling. Using phosphoinositide binding protein probes, we observed increased levels of PI(3)P, PI(4)P, PI(3,4)P₂, PI(4,5)P2, and PI(3,4,5)P₃ in PTP1B knockout mouse retina and decreased levels of these PIPs in Grb14 knockout mouse retina. These observations suggest that the interplay between PTP1B and Grb14 can regulate PIP metabolism.