bims-raghud 2024-06-02 papers

Issue of 2024–06–02
five papers selected by
Irene Sambri, TIGEM

Cardiorenal Med. 2024 May 29.

Kidney replacement therapies and ultrafiltration in cardiorenal syndrome.

Luz Yareli Villegas-Gutiérrez, Julio Núñez, Kianoush Kashani, Jonathan S Chávez-Iñiguez.

BACKGROUND: Some patients with cardiorenal syndrome 1 and congestion exhibit resistance to diuretics. This scenario complicates management and is associated with a worse prognosis. In some cases, rescue treatment may be considered by starting kidney replacement therapies or ultrafiltration. This decision is complex and necessitates a profound understanding of these techniques and the pathophysiology of this syndrome. These modalities are classified into continuous, intermittent, and ultrafiltration therapies, each with its own advantages and disadvantages that are pertinent in selecting the optimal treatment.
SUMMARY: In patients with diuretic-resistant cardiorenal syndrome, extracorporeal ultrafiltration and kidney replacement therapies have the potential to relieve congestion, restore the neurohormonal system, and improve quality of life.
KEY MESSAGE: • In cardiorenal syndrome the resistance to diuretics it is common. • Extracorporeal ultrafiltration and renal replacement therapies are rescue options that may improve the management of these patients. • Better understanding of these modalities will help the development of new devices which are friendlier, safer, and more affordable for patients in these clinical settings.

DOI: https://doi.org/10.1159/000539547

Sci Rep. 2024 May 31. 14(1): 12521

Regulation of TSC2 lysosome translocation and mitochondrial turnover by TSC2 acetylation status.

Patricia Marqués, Jesús Burillo, Carlos González-Blanco, Beatriz Jiménez, Gema García, Ana García-Aguilar, Sarai Iglesias-Fortes, Ángela Lockwood, Carlos Guillén.

Sirtuin1 (SIRT1) activity decreases the tuberous sclerosis complex 2 (TSC2) lysine acetylation status, inhibiting the mechanistic target of rapamycin complex 1 (mTORC1) signalling and concomitantly, activating autophagy. This study analyzes the role of TSC2 acetylation levels in its translocation to the lysosome and the mitochondrial turnover in both mouse embryonic fibroblast (MEF) and in mouse insulinoma cells (MIN6) as a model of pancreatic β cells. Resveratrol (RESV), an activator of SIRT1 activity, promotes TSC2 deacetylation and its translocation to the lysosome, inhibiting mTORC1 activity. An improvement in mitochondrial turnover was also observed in cells treated with RESV, associated with an increase in the fissioned mitochondria, positive autophagic and mitophagic fluxes and an enhancement of mitochondrial biogenesis. This study proves that TSC2 in its deacetylated form is essential for regulating mTORC1 signalling and the maintenance of the mitochondrial quality control, which is involved in the homeostasis of pancreatic beta cells and prevents from several metabolic disorders such as Type 2 Diabetes Mellitus.

Keywords: Acetylation; Lysosome; Mitophagy; Pancreatic β cells; TSC2; mTORC1

DOI: https://doi.org/10.1038/s41598-024-63525-7

bioRxiv. 2024 May 14. pii: 2024.05.13.594044. [Epub ahead of print]

Hyperactive mTORC1/4EBP1 Signaling Dysregulates Proteostasis and Accelerates Cardiac Aging.

Weronika Zarzycka, Kamil A Kobak, Catherine J King, Frederick F Peelor, Benjamin F Miller, Ying Ann Chiao.

The mechanistic target of rapamycin complex 1 (mTORC1) has a major impact on aging by regulation of proteostasis. It is well established that mTORC1 signaling is hyperactivated with aging and age-related diseases. Previous studies have shown that partial inhibition of mTOR signaling by rapamycin reverses the age-related decline in cardiac function and structure in old mice. However, the downstream signaling pathways involved in this protection against cardiac aging have not been established. TORC1 phosphorylates 4E-binding protein 1 (4EBP1) to promote the initiation of cap-dependent translation. The aim of this project is to examine the role of the mTORC1/4EBP1 axis in age-related cardiac dysfunction. We utilized a whole-body 4EBP1 KO mouse model, which mimics a hyperactive 4EBP1/eIF4E axis, to investigate the effects of hyperactive mTORC1/4EBP1 axis in cardiac aging. Echocardiographic measurements revealed that young 4EBP1 KO mice have no difference in cardiac function at baseline compared to WT mice. Interestingly, middle-aged (14-15-month-old) 4EBP1 KO mice show impaired diastolic function and myocardial performance compared to age-matched WT mice and their diastolic function and myocardial performance are at similar levels as 24-month-old WT mice, suggesting that 4EBP1 KO mice experience accelerated cardiac aging. Old 4EBP1 KO mice show further declines in systolic and diastolic function compared to middle-aged 4EBP1 KO mice and have worse systolic and diastolic function than age-matched old WT mice. Gene expression levels of heart failure markers are not different between 4EBP1 KO and WT mice at these advanced ages. However, ribosomal biogenesis and overall protein ubiquitination are significantly increased in 4EBP1 KO mice when compared to WT, which suggests dysregulated proteostasis. Together, these results show that a hyperactive 4EBP1/eIF4E axis accelerates cardiac aging, potentially by dysregulating proteostasis.

DOI: https://doi.org/10.1101/2024.05.13.594044

Adv Sci (Weinh). 2024 May 29. e2308556

Kidney Organoid Modeling of WT1 Mutations Reveals Key Regulatory Paths Underlying Podocyte Development.

Gang Wang, Hangdi Wu, Xiuwen Zhai, Li Zhang, Changming Zhang, Chen Cheng, Xiaodong Xu, Erzhi Gao, Xushen Xiong, Jin Zhang, Zhihong Liu.

Wilms tumor-1(WT1) is a crucial transcription factor that regulates podocyte development. However, the epigenomic mechanism underlying the function of WT1 during podocyte development has yet to be fully elucidated. Here, single-cell chromatin accessibility and gene expression maps of foetal kidneys and kidney organoids are generated. Functional implications of WT1-targeted genes, which are crucial for the development of podocytes and the maintenance of their structure, including BMPER/PAX2/MAGI2 that regulates WNT signaling pathway, MYH9 that maintains actin filament organization and NPHS1 that modulates cell junction assembly are identified. To further illustrate the functional importance of WT1-mediated transcriptional regulation during podocyte development, cultured and implanted patient-derived kidney organoids derived from the Induced Pluripotent Stem Cell (iPSCs) of a patient with a heterozygous missense mutation in WT1 are generated. Results from single-cell RNA sequencing (scRNA-seq) and functional assays confirm that the WT1 mutation leads to delays in podocyte development and causes damage to cell structures, due to its failure to activate the targeting genes MAGI2, MYH9, and NPHS1. Notably, correcting the mutation in the patient iPSCs using CRISPR-Cas9 gene editing rescues the podocyte phenotype. Collectively, this work elucidates the WT1-related epigenomic landscape with respect to human podocyte development and identifies the disease-causing role of a WT1 mutation.

Keywords: WT1; kidney organoid; podocyte development; scATAC‐seq; scRNA‐seq

DOI: https://doi.org/10.1002/advs.202308556

FASEB J. 2024 May 31. 38(10): e23703

Transport activity regulates mitochondrial bioenergetics and biogenesis in renal tubules.

Chih-Jen Cheng, Jonathan M Nizar, Dao-Fu Dai, Chou-Long Huang.

Renal tubules are featured with copious mitochondria and robust transport activity. Mutations in mitochondrial genes cause congenital renal tubulopathies, and changes in transport activity affect mitochondrial morphology, suggesting mitochondrial function and transport activity are tightly coupled. Current methods of using bulk kidney tissues or cultured cells to study mitochondrial bioenergetics are limited. Here, we optimized an extracellular flux analysis (EFA) to study mitochondrial respiration and energy metabolism using microdissected mouse renal tubule segments. EFA detects mitochondrial respiration and glycolysis by measuring oxygen consumption and extracellular acidification rates, respectively. We show that both measurements positively correlate with sample sizes of a few centimeter-length renal tubules. The thick ascending limbs (TALs) and distal convoluted tubules (DCTs) critically utilize glucose/pyruvate as energy substrates, whereas proximal tubules (PTs) are significantly much less so. Acute inhibition of TALs' transport activity by ouabain treatment reduces basal and ATP-linked mitochondrial respiration. Chronic inhibition of transport activity by 2-week furosemide treatment or deletion of with-no-lysine kinase 4 (Wnk4) decreases maximal mitochondrial capacity. In addition, chronic inhibition downregulates mitochondrial DNA mass and mitochondrial length/density in TALs and DCTs. Conversely, gain-of-function Wnk4 mutation increases maximal mitochondrial capacity and mitochondrial length/density without increasing mitochondrial DNA mass. In conclusion, EFA is a sensitive and reliable method to investigate mitochondrial functions in isolated renal tubules. Transport activity tightly regulates mitochondrial bioenergetics and biogenesis to meet the energy demand in renal tubules. The system allows future investigation into whether and how mitochondria contribute to tubular remodeling adapted to changes in transport activity.

Keywords: distal convoluted tubule; extracellular flux analysis; glycolysis; mitochondrial respiration; thick ascending limb; transport activity

DOI: https://doi.org/10.1096/fj.202400358RR