SUMMARY Progranulin (GRN) and TMEM106B are associated with several common neurodegenerative disorders including frontotemporal lobar degeneration (FTLD). A TMEM106B variant modifies GRN-associated FTLD risk. However, their functional relationship in vivo and the mechanisms underlying the risk modification remain unclear. Here, using transcriptomic and proteomic analyses with Grn−/− and Tmem106b−/− mice, we show that while multiple lysosomal enzymes are increased in Grn−/− brain at both transcriptional and protein levels, TMEM106B deficiency causes reduction in several lysosomal enzymes. Remarkably, Tmem106b deletion from Grn−/− mice normalizes lysosomal protein levels and rescues FTLD-related behavioral abnormalities and retinal degeneration, without improving lipofuscin, C1q or microglial accumulation. Mechanistically, TMEM106B binds vacuolar-ATPase accessory protein 1 (AP1). TMEM106B deficiency reduces vacuolar-ATPase AP1 and V0 subunits, impairing lysosomal acidification and normalizing lysosomal protein levels in Grn−/− neurons. Thus, Grn and Tmem106b genes have opposite effects on lysosomal enzyme levels, and their interaction determines the extent of neurodegeneration.

SUMMARY Many bacterial pathogens and symbionts utilize type III secretion systems to deliver bacterial effector proteins into host cells. These effector proteins have the capacity to modulate a large variety of cellular functions in a highly regulated manner. Here we report that the phosphoinositide phosphatase SopB, a Salmonella Typhimurium type III secreted effector protein, diversifies its function by localizing to different cellular compartments in a ubiquitin-dependent manner. We show that SopB utilizes the same enzymatic activity to modulate actin-mediated bacterial internalization and Akt activation at the plasma membrane, and vesicular traffic and intracellular bacterial replication at the phagosome. Thus by exploiting the host cellular machinery, Salmonella Typhimurium has evolved the capacity to broaden the functional repertoire of a virulence factor to maximize its ability to modulate cellular functions.

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This study identifies an unusual sulfur-based chemical as a novel and specific inhibitor of the tyrosine phosphatase STEP and shows that it can improve the cognitive function of a mouse model of Alzheimer's disease.

Detailed observations of transcriptional, translational, and post-translational events in the human brain are essential to improving our understanding of its development, function, and vulnerability to disease. Here, we exploited label-free quantitative tandem mass-spectrometry proteomics to create an in-depth proteomic survey of adult human brain regions. Integration of protein data with existing whole-transcriptome sequencing (RNA-seq) from the BrainSpan project revealed varied patterns of protein:RNA relationships with generally increased magnitudes of protein abundance differences between brain regions compared to RNA. Many of the differences amplified in protein data were reflective of cyto-architectural and functional variation between brain regions. Comparing structurally similar cortical regions revealed significant differences in the abundance of receptor-associated and resident plasma membrane proteins that were not readily observed in the RNA expression data.

To characterize the intersubunit interactions underlying assembly and maturation in HIV-1, we determined the amide hydrogen exchange protection pattern of capsid protein in the immature virion and the mature virion using mass spectrometry. Alterations in protection upon maturation provide evidence for the maturation-induced formation of an interaction between the N- and C-terminal domains in half of the capsid molecules, indicating that only half of the capsid protein is assembled into the conical core.

Hypertension contributes to the global burden of cardiovascular disease. Increased dietary K + reduces blood pressure; however, the mechanism has been obscure. Human genetic studies have suggested that the mechanism is an obligatory inverse relationship between renal salt reabsorption and K + secretion. Mutations in the kinases with-no-lysine 4 (WNK4) or WNK1, or in either Cullin 3 (CUL3) or Kelch-like 3 (KLHL3)-components of an E3 ubiquitin ligase complex that targets WNKs for degradation-cause constitutively increased renal salt reabsorption and impaired K + secretion, resulting in hypertension and hyperkalemia. The normal mechanisms that regulate the activity of this ubiquitin ligase and levels of WNKs have been unknown. We posited that missense mutations in KLHL3 that impair binding of WNK4 might represent a phenocopy of the normal physiologic response to volume depletion in which salt reabsorption is maximized. We show that KLHL3 is phosphorylated at serine 433 in the Kelch domain (a site frequently mutated in hypertension with hyperkalemia) by protein kinase C in cultured cells and that this phosphorylation prevents WNK4 binding and degradation. This phosphorylation can be induced by angiotensin II (AII) signaling. Consistent with these in vitro observations, AII administration to mice, even in the absence of volume depletion, induces renal KLHL3 S433 phosphorylation and increased levels of both WNK4 and the NaCl cotransporter. Thus, AII, which is selectively induced in volume depletion, provides the signal that prevents CUL3/KLHL3-mediated degradation of WNK4, directing the kidney to maximize renal salt reabsorption while inhibiting K + secretion in the setting of volume depletion.renin-angiotensin-aldosterone system | distal tubule | hypertension | posttranslational modification | PHAII H ypertension affects 1 billion people worldwide and is a major risk factor for death from stroke, myocardial infarction, and congestive heart failure. The study of Mendelian forms of hypertension has demonstrated the key role of increased renal salt reabsorption in disease pathogenesis (1-4). Observational and intervention trials (5, 6) also indicate that increased dietary K + lowers blood pressure; however, the mechanism of this effect has been unclear.Pseudohypoaldosteronism type II (PHAII; Online Mendelian Inheritance in Man no. 145260), featuring hypertension and hyperkalemia, has revealed a previously unrecognized mechanism that regulates the balance between renal salt reabsorption and K + secretion in response to aldosterone (7). Aldosterone is produced by the adrenal glomerulosa in volume depletion, in response to angiotensin II (AII), and in hyperkalemia via membrane depolarization (8). In volume depletion, aldosterone maximizes renal salt reabsorption, whereas in hyperkalemia, aldosterone promotes maximal renal K + secretion. Volume depletion increases both the NaCl cotransporter (NCC) (9) and electrogenic Na + reabsorption via the epithelial Na + channel (ENaC) (10). The lumen-negative potential produced by ENa...

Dysregulation of several metabolite pathways, including branched-chain amino acids (BCAAs), are associated with Non-Alcoholic Fatty Liver Disease (NAFLD) and insulin resistance in adults, while studies in youth reported conflicting results. We explored whether, independently of obesity and insulin resistance, obese adolescents with NAFLD display a metabolomic signature consistent with disturbances in amino acid and lipid metabolism. A total of 180 plasma metabolites were measured by a targeted metabolomic approach in 78 obese adolescents with (n = 30) or without (n = 48) NAFLD assessed by magnetic resonance imaging (MRI). All subjects underwent an oral glucose tolerance test and subsets of patients underwent a two-step hyperinsulinemic-euglycemic clamp and/or a second MRI after a 2.2 ± 0.8-year follow-up. Adolescents with NAFLD had higher plasma levels of valine (p = 0.02), isoleucine (p = 0.03), tryptophan (p = 0.02), and lysine (p = 0.02) after adjustment for confounding factors. Circulating BCAAs were negatively correlated with peripheral and hepatic insulin sensitivity. Furthermore, higher baseline valine levels predicted an increase in hepatic fat content (HFF) at follow-up (p = 0.01). These results indicate that a dysregulation of BCAA metabolism characterizes obese adolescents with NAFLD independently of obesity and insulin resistance and predict an increase in hepatic fat content over time.