Evaluation of gliovascular functions of AQP4 readthrough isoforms.

Aquaporin-4 (AQP4) is a water channel protein that links the astrocytic endfeet to the blood-brain barrier (BBB) and regulates water and potassium homeostasis in the brain, as well as the glymphatic clearance of waste products that would otherwise potentiate neurological diseases. Recently, translational readthrough was shown to generate a C-terminally extended variant of AQP4, known as AQP4x, which preferentially localizes around the BBB through interaction with the scaffolding protein α-syntrophin, and loss of AQP4x disrupts waste clearance from the brain. To investigate the function of AQP4x, we generated a novel AQP4 mouse line (AllX) to increase relative levels of the readthrough variant above the ~15% of AQP4 in the brain of wild-type (WT) mice. We validated the line and assessed characteristics that are affected by the presence of AQP4x, including AQP4 and α-syntrophin localization, integrity of the BBB, and neurovascular coupling. We compared AllXHom and AllXHet mice to WT and to previously characterized AQP4 NoXHet and NoXHom mice, which cannot produce AQP4x. An increased dose of AQP4x enhanced perivascular localization of α-syntrophin and AQP4, while total protein expression of the two was unchanged. However, at 100% readthrough, AQP4x localization and the formation of higher order complexes were disrupted. Electron microscopy showed that overall blood vessel morphology was unchanged except for an increased proportion of endothelial cells with budding vesicles in NoXHom mice, which may correspond to a leakier BBB or altered efflux that was identified in NoX mice using MRI. These data demonstrate that AQP4x plays a small but measurable role in maintaining BBB integrity as well as recruiting structural and functional support proteins to the blood vessel. This also establishes a new set of genetic tools for quantitatively modulating AQP4x levels.

Evaluation of gliovascular functions of Aqp4 readthrough isoforms.

Aquaporin-4 (AQP4) is a water channel protein that links astrocytic endfeet to the blood-brain barrier (BBB) and regulates water and potassium homeostasis in the brain, as well as the glymphatic clearance of waste products that would otherwise potentiate neurological diseases. Recently, translational readthrough was shown to generate a C-terminally extended variant of AQP4, known as AQP4x, that preferentially localizes around the BBB through interaction with the scaffolding protein α-syntrophin, and loss of AQP4x disrupts waste clearance from the brain. To investigate the function of AQP4x, we generated a novel mouse AQP4 line (AllX) to increase relative levels of the readthrough variant above the ~15% of AQP4 in the brain of wildtype (WT) mice. We validated the line and assessed characteristics that are affected by the presence of AQP4x, including AQP4 and α-syntrophin localization, integrity of the BBB, and neurovascular coupling. We compared AllXHom and AllXHet mice to wildtype, and to previously characterized AQP4 NoXHet and NoXHom mice, which cannot produce AQP4x. Increased dose of AQP4x enhanced perivascular localization of α-syntrophin and AQP4, while total protein expression of the two were unchanged. However, at 100% readthrough, AQP4x localization and formation of higher-order complexes was disrupted. Electron microscopy showed that overall blood vessel morphology was unchanged except for increased endothelial cell vesicles in NoXHom mice, which may correspond to a leakier BBB or altered efflux that was identified in NoX mice using MRI. These data demonstrate that AQP4x plays a small but measurable role in maintaining BBB integrity as well as recruiting structural and functional support proteins to the blood vessel. This also establishes a new set of genetic tools for quantitatively modulating AQP4x levels.

Local translation in microglial processes is required for efficient phagocytosis.

Neurons, astrocytes and oligodendrocytes locally regulate protein translation within distal processes. Here, we tested whether there is regulated local translation within peripheral microglial processes (PeMPs) from mouse brain. We show that PeMPs contain ribosomes that engage in de novo protein synthesis, and these are associated with transcripts involved in pathogen defense, motility and phagocytosis. Using a live slice preparation, we further show that acute translation blockade impairs the formation of PeMP phagocytic cups, the localization of lysosomal proteins within them, and phagocytosis of apoptotic cells and pathogen-like particles. Finally, PeMPs severed from their somata exhibit and require de novo local protein synthesis to effectively surround pathogen-like particles. Collectively, these data argue for regulated local translation in PeMPs and indicate a need for new translation to support dynamic microglial functions.

Yeast Puf3p-mediated mRNA decay is regulated by carbon source-specific differential interaction of Puf3p with Pop2p and Yak1p.

Puf3p regulates the stability of nuclear-encoded mRNAs acting in mitochondrial biogenesis and function in Saccharomyces cerevisiae. This work identifies the phosphorylation of Pop2p, a component of the deadenylase complex, as being critical for adapting Puf3p-mediated mRNA decay upon carbon source alterations. We demonstrate that the Puf3p-Pop2p association diminishes in mitochondria-reliant conditions and establish Yak1p, a kinase that phosphorylates Pop2p at threonine 97, as a new player in Puf3p-mediated regulation of mRNA decay. Yak1p deletion alters the half-life of Puf3p target mRNAs. Our findings outline a metabolism-driven regulatory switch, whereby, in mitochondria-independent conditions, Puf3p recruits Pop2p and the decay machinery to bound mRNAs for rapid decay. Conversely, in mitochondria-reliant conditions, the association of Puf3p with Yak1p increases, placing Yak1p proximal to neighboring Pop2p. Subsequent Pop2p phosphorylation reduces the Puf3p-Pop2p interaction and stabilizes Puf3p target mRNAs.