Lipophagy maintains energy homeostasis in the kidney proximal tubule during prolonged starvation

Macroautophagy/autophagy is a self-degradation process that combats starvation. Lipids are the main energy source in kidney proximal tubular cells (PTCs). During starvation, PTCs increase fatty acid (FA) uptake, form intracellular lipid droplets (LDs), and hydrolyze them for use. The involvement of autophagy in lipid metabolism in the kidney remains largely unknown. Here, we investigated the autophagy-mediated regulation of renal lipid metabolism during prolonged starvation using PTC-specific Atg5-deficient (atg5-TSKO) mice and an in vitro serum starvation model. Twenty-four h of starvation comparably induced LD formation in the PTCs of control and atg5-TSKO mice; however, additional 24 h of starvation reduced the number of LDs in control mice, whereas increases were observed in atg5-TSKO mice. Autophagic degradation of LDs (lipophagy) in PTCs was demonstrated by electron microscopic observation and biochemical analysis. In vitro pulse-chase assays demonstrated that lipophagy mobilizes FAs from LDs to mitochondria during starvation, whereas impaired LD degradation in autophagy-deficient PTCs led to decreased ATP production and subsequent cell death. In contrast to the in vitro assay, despite impaired LD degradation, kidney ATP content was preserved in 48-h starved atg5-TSKO mice, probably due to increased utilization of ketone bodies. This compensatory mechanism was accompanied by a higher plasma FGF21 (fibroblast growth factor 21) level and its expression in the PTCs; however, this was not essential for the production of ketone bodies in the liver during prolonged starvation. In conclusion, lipophagy combats prolonged starvation in PTCs to avoid cellular energy depletion.     

Effects of magnesium deficiency on magnesium uptake activity of rice root,evaluated using <Superscript>28</Superscript> Mg as a tracer

Aims

The mechanisms underlying magnesium (Mg) uptake by plant roots remain to be fully elucidated. In particular, there is little information about the effects of Mg deficiency on Mg uptake activity. A Mg uptake kinetic study is essential for better understanding the Mg uptake system.

Methods

We performed a Mg uptake tracer experiment in rice plants using ²⁸?Mg.

Results

Mg uptake was mediated by high- and low-affinity transport systems. The K _m value of the high-affinity transport system was approximately 70 μM under Mg-deficient conditions. The Mg uptake activity was promoted by Mg deficiency, which in turn fell to the basal level after 5- min of Mg resupply. The induced uptake rate was inhibited by ionophore treatment, suggesting that an energy-dependent uptake system is enhanced by Mg deficiency.

Conclusions

The Mg uptake changes rapidly with Mg conditions in rice, as revealed by a ²⁸?Mg tracer experiment. This technique is expected to be applicable for Mg uptake analyses, particularly in mutants or other lines.

     

ER stress-induced protein, VIGG, disturbs plant cation homeostasis, which is correlated with growth retardation and robustness to ER stress

VIGG is a putative endoplasmic reticulum (ER) resident protein induced by virus infection and ER stress, and is correlated with fruit quality in grapevine. The present study was undertaken to determine the biological function of VIGG in grapevine. Experiments using fluorescent protein-VIGG fusion protein demonstrated that VIGG is localized in ER and the ER targeting sequence is in the N-terminus. The overexpression of VIGG in Arabidopsis plant led to growth retardation. The rosette leaves of VIGG-overexpressing plants were smaller than those of the control plants and rolled at 42 days after seeding. VIGG-overexpressing plants revealed robustness to ER stress as well as the low expression of ER stress marker proteins, such as the luminal binding proteins. These characteristics of VIGG-overexpressing plants were supported by a microarray experiment that demonstrated the disruption of genes related to ER stress response and flowering, as well as cation mobility, in the plants. Finally, cation homeostasis in the plants was disturbed by the overexpression of VIGG. Taken together, these results suggest that VIGG may disturb cation homeostasis in plant, which is correlated with the robustness to ER stress and growth retardation.     

Working memory deficits in neuronal nitric oxide synthase knockout mice: potential impairments in prefrontal cortex mediated cognitive function

Neuronal nitric oxide synthase (nNOS) forms nitric oxide (NO), which functions as a signaling molecule via S-nitrosylation of various proteins and regulation of soluble guanylate cyclase (cGC)/cyclic guanosine monophosphate (cGMP) pathway in the central nervous system. nNOS signaling regulates diverse cellular processes during brain development and molecular mechanisms required for higher brain function. Human genetics have identified nNOS and several downstream effectors of nNOS as risk genes for schizophrenia. Besides the disease itself, nNOS has also been associated with prefrontal cortical functioning, including cognition, of which disturbances are a core feature of schizophrenia. Although mice with genetic deletion of nNOS display various behavioral deficits, no studies have investigated prefrontal cortex-associated behaviors. Here, we report that nNOS knockout (KO) mice exhibit hyperactivity and impairments in contextual fear conditioning, results consistent with previous reports. nNOS KO mice also display mild impairments in object recognition memory. Most importantly, we report for the first time working memory deficits, potential impairments in prefrontal cortex mediated cognitive function in nNOS KO mice. Furthermore, we demonstrate Disrupted-in-Schizophrenia 1 (DISC1), another genetic risk factor for schizophrenia that plays roles for cortical development and prefrontal cortex functioning, including working memory, is a novel protein binding partner of nNOS in the developing cerebral cortex. Of note, genetic deletion of nNOS appears to increase the binding of DISC1 to NDEL1, regulating neurite outgrowth as previously reported. These results suggest that nNOS KO mice are useful tools in studying the role of nNOS signaling in cortical development and prefrontal cortical functioning.     

Basophil-derived mouse mast cell protease 11 induces microvascular leakage and tissue edema in a mast cell-independent manner

Mouse mast cell protease 11 (mMCP-11) is the most recently identified member of the mouse mast cell tryptase family. This tryptase is preferentially produced by basophils in contrast to other members that are expressed by mast cells but not basophils. Although blood-circulating basophils have long been considered as minor and redundant relatives of tissue-resident mast cells, recent studies illustrated that basophils and mast cells play distinct roles in vivo. To explore the in vivo role of basophil-derived mMCP-11, here we prepared recombinant mMCP-11 and its protease-dead mutant. Subcutaneous injection of the wild-type mMCP-11 but not the mutant induced edematous skin swelling with increased microvascular permeability in a dose-dependent manner. No apparent infiltration of proinflammatory cells including neutrophils and eosinophils was detected in the skin lesions. The cutaneous swelling was abolished by the pretreatment of mice with indomethacin, a cyclooxygenase inhibitor, suggesting the major contribution of prostaglandins to the microvascular leakage. Of note, the cutaneous swelling was elicited even in mast cell-deficient mice, indicating that mast cells are dispensable for the mMCP-11-induced cutaneous swelling. Thus, basophil-derived mMCP-11 can induce microvascular leakage via prostaglandins in a mast cell-independent manner, and may contribute to the development of basophil-mediated inflammatory responses.     

Mature and juvenile tissue models of regeneration in small fish species

The multitude of cells constituting organisms are fragile and easily damaged day by day. Therefore, maintenance of tissue morphology and function is fundamental for multicellular organisms to attain long life. For proper maintenance of tissue integrity, organisms must have mechanisms that detect the loss of tissue mass, activate the de novo production of cells, and organize those cells into functional tissues. However, these processes are only poorly understood. Here we give an overview of adult and juvenile tissue regeneration models in small fish species, such as zebrafish and medaka, and highlight recent advances at the molecular level. From these advances, we have come to realize that the epidermal and mesenchymal parts of the regenerating fish fin-that is, the wound epidermis and blastema, respectively-comprise heterogeneous populations of cells with different molecular identities that can be termed "compartments." These compartments and their mutual interactions are thought to play important roles in promoting the proper progression of tissue regeneration. We further describe the current understanding of these compartments and discuss the possible approaches to affording a better understanding of their roles and interactions during regeneration.