Gaining a foothold on kidney disease?: The leading cause of kidney disease worldwide is known as focal segmental glomerulosclerosis (FSGS). FSGS is associated with loss of podocytes, an unusual cell type critical for the kidney's blood filtration function. Podocytes form interdigitating foot processes that wrap around capillaries and prevent leakage of plasma proteins into urine (proteinuria). Zhou et al. suppressed proteinuria by preventing podocyte loss in two different rat models of kidney disease, using a compound that selectively inhibits the TRPC5 ion channel (see the Perspective by Chung and Shaw). In short-term studies, this compound had no detectable side effects. Thus, TRPC5 inhibitors may merit exploration as a therapy for progressive kidney disease. Science , this issue p. 1332 ; see also p. 1256

The trafficking dynamics of uromodulin (UMOD), the most abundant protein in human urine, play a critical role in the pathogenesis of kidney disease. Monoallelic mutations in the UMOD gene cause autosomal dominant tubulointerstitial kidney disease (ADTKD- UMOD ), an incurable genetic disorder that leads to kidney failure. The disease is caused by the intracellular entrapment of mutant UMOD in kidney epithelial cells, but the precise mechanisms mediating disrupted UMOD trafficking remain elusive. Here, we report that transmembrane Emp24 protein transport domain–containing (TMED) cargo receptors TMED2, TMED9, and TMED10 bind UMOD and regulate its trafficking along the secretory pathway. Pharmacological targeting of TMEDs in cells, in human kidney organoids derived from patients with ADTKD- UMOD , and in mutant- UMOD -knockin mice reduced intracellular accumulation of mutant UMOD and restored trafficking and localization of UMOD to the apical plasma membrane. In vivo, the TMED-targeted small molecule also mitigated ER stress and markers of kidney damage and fibrosis. Our work reveals TMED-targeting small molecules as a promising therapeutic strategy for kidney proteinopathies.

Key Points: The clinical significance of a number of missense variants of α-galactosidase A is often ambiguous. Defective proteostasis of some missense α-galactosidase A variants induced chronic endoplasmic reticulum stress and the unfolded protein response. Endoplasmic reticulum stress and the unfolded protein response may explain clinical manifestations of non-classic Fabry disease. Background: Classic Fabry disease is caused by GLA mutations that result in loss of enzymatic activity of α-galactosidase A, lysosomal storage of globotriaosylceramide, and a resulting multisystemic disease. In non-classic Fabry disease, patients have some preserved α-galactosidase A activity and a milder disease course. Heterozygous female patients may also be affected. While Fabry disease pathogenesis has been mostly attributed to catalytic deficiency of mutated α-galactosidase A, lysosomal storage, and impairment of lysosomal functions, other pathogenic factors may contribute, especially in nonclassic Fabry disease. Methods: We characterized the genetic, clinical, biochemical, molecular, cellular, and organ pathology correlates of the p.L394P α-galactosidase A variant that was identified initially in six individuals with kidney failure by the Czech national screening program for Fabry disease and by further screening in an additional 24 family members. Results: Clinical findings in affected male patients revealed a milder clinical course, with approximately 15% residual α-galactosidase A activity with normal plasma lyso-globotriaosylceramide levels and abnormally low ratio of these values. None of the four available kidney biopsies showed lysosomal storage. Laboratory investigations documented intracellular retention of mutated α-galactosidase A with resulting endoplasmic reticulum stress and the unfolded protein response, which were alleviated with BRD4780, a small molecule clearing misfolded proteins from the early secretory compartment. We observed similar findings of endoplasmic reticulum stress and unfolded protein response in five kidney biopsies with several other classic and non-classic Fabry disease missense α-galactosidase A variants. Conclusions: We identified defective proteostasis of mutated α-galactosidase A resulting in chronic endoplasmic reticulum stress and unfolded protein response of α-galactosidase A expressing cells as a contributor to Fabry disease pathogenesis.

Background: The cellular proteostasis machinery is essential for maintaining protein homeostasis by employing quality control systems that identify, sequester, and eliminate damaged or misfolded proteins. However, the accumulation of misfolded proteins can overwhelm these protective mechanisms, disrupting proteostasis. This phenomenon is a hallmark of numerous pathologies, including a variety of genetic disorders. In the secretory pathway, the buildup of misfolded proteins triggers endoplasmic reticulum (ER) stress, which activates the unfolded protein response (UPR). The UPR serves as an adaptive mechanism, aiming to alleviate stress and restore cellular homeostasis. However, if ER stress is prolonged or severe, the UPR may fail to restore balance and apoptosis is induced. Summary: This review introduces the intricate signaling pathways activated by the three UPR transmembrane sensors: protein-kinase R-like endoplasmic reticulum kinase (PERK), inositol requiring enzyme 1 (IRE1), and activating transcription factor 6 (ATF6). We briefly present the roles of the distinct transcriptional programs activated by each sensor in modulating the cellular response to protein stress and in determining cell fate. We discuss how genetic variants and environmental factors contribute to the heterogeneity observed in protein misfolding diseases. Finally, we critically evaluate select therapeutic strategies, specifically protein stabilization, trafficking modulation, and UPR sensor targeting approaches. Key Messages: This review introduces the potential consequences of protein misfolding, which may not only impair protein function but can also lead to toxic protein accumulation and stress induction. Using Fabry disease as a compelling example, we suggest that future therapeutic intervention may require nuanced, combination approaches that address both loss and gain of protein function.

Bipolar disorder (BD) is a severe and common chronic mental illness characterized by recurrent mood swings between depression and mania. The biological basis of the disease is poorly understood, and its treatment is unsatisfactory. Na⁺, K⁺-ATPase is a major plasma membrane transporter and signal transducer. The catalytic α subunit of this enzyme is the binding site for cardiac steroids. Three α isoforms of the Na⁺, K⁺-ATPase are present in the brain. Previous studies have supported the involvement of the Na⁺, K⁺-ATPase and endogenous cardiac steroids (ECS) in the etiology of BD. Decreased brain ECS has been found to elicit anti-manic and anti-depressive-like behaviors in mice and rats. However, the identity of the specific α isoform involved in these behavioral effects is unknown. Here, we demonstrated that decreasing ECS through intracerebroventricular (i.c.v.) administration of anti-ouabain antibodies (anti-Ou-Ab) decreased the activity of α1^+/− mice in forced swimming tests but did not change the activity in wild type (wt) mice. This treatment also affected exploratory and anxiety behaviors in α1^+/− but not wt mice, as measured in open field tests. The i.c.v. administration of anti-Ou-Ab decreased brain ECS and increased brain Na⁺, K⁺-ATPase activity in wt and α1^+/− mice. The serum ECS was lower in α1^+/− than wt mice. In addition, a study in human participants demonstrated that serum ECS significantly decreased after treatment. These results suggest that the Na⁺, K⁺-ATPase α1 isoform is involved in depressive- and manic-like behaviors and support that the Na⁺, K⁺-ATPase/ECS system participates in the etiology of BD.

Glioblastoma is one of the most aggressive and lethal forms of brain cancer, with limited therapeutic options and poor patient prognosis. Recent research has identified the TMED family of proteins as key regulators of tumor progression and aggressiveness across multiple cancer types. TMED members are cargo receptors expressed within the early secretory pathway and involved in bidirectional traffic of various proteins including EGFR, TGF-ɑ and WNT. In this study, we explored the therapeutic potential of genetic and pharmacologic inhibition of the cargo receptor TMED9 in glial tumor models. Our findings demonstrate that TMED9 expression is upregulated in glioma and that this upregulation is associated with poor patient survival. Using patient-derived glioma tumor cells, we demonstrate that TMED9 is highly expressed in the cancer stem cell population and that this upregulation promotes the cells’ self-renewal and migration. This is the first time, to the best of our knowledge, that TMED9 has been shown to play a major role in the function and tumorigenesis of brain tumor cancer stem cells. BRD4780, a small molecule that targets TMED9, effectively reduced TMED9 abundance, resulting in decreased viability, migration and stemness of patient-derived glioma stem cells. Moreover, BRD4780 mitigated the proliferation and migration of differentiated glioma tumor cells. When applied together with temozolomide, an established glioblastoma treatment, BRD4780 elicited an enhanced anti-tumor response. Lastly, to demonstrate the broad applicability of our findings, we targeted TMED9 in pediatric glioma cells and showed efficient inhibition of various oncogenic functions. Collectively, our study identifies TMED9 inhibition as a promising therapeutic approach that impairs the tumorigenesis and aggressiveness of brain tumors, with high efficacy against the tumor stem cell population. The effectiveness of TMED9 targeting in different tumor cell populations, the potential of combining this strategy with established therapies and the broad applicability of this approach to multiple cancer types highlight the significance of these findings.