CaMKII as a pathological mediator of ER stress, oxidative stress, and mitochondrial dysfunction in a murine model of nephronophthisis.

Polycystic kidney diseases (PKDs) are genetic diseases characterized by renal cyst formation with increased cell proliferation, apoptosis, and transition to a secretory phenotype at the expense of terminal differentiation. Despite recent progress in understanding PKD pathogenesis and the emergence of potential therapies, the key molecular mechanisms promoting cystogenesis are not well understood. Here, we demonstrate that mechanisms including endoplasmic reticulum stress, oxidative damage, and compromised mitochondrial function all contribute to nephronophthisis-associated PKD. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is emerging as a critical mediator of these cellular processes. Therefore, we reasoned that pharmacological targeting of CaMKII may translate into effective inhibition of PKD in jck mice. Our data demonstrate that CaMKII is activated within cystic kidney epithelia in jck mice. Blockade of CaMKII with a selective inhibitor results in effective inhibition of PKD in jck mice. Mechanistic experiments in vitro and in vivo demonstrated that CaMKII inhibition relieves endoplasmic reticulum stress and oxidative damage and improves mitochondrial integrity and membrane potential. Taken together, our data support CaMKII inhibition as a new and effective therapeutic avenue for the treatment of cystic diseases.

How Much Time Do Focal Treatments for Retinoblastoma Add to Anesthetic Exposure?

Introduction: Children with retinoblastoma have anesthesia for exams and treatment, but there is little information about how long treatment interventions (laser, cryotherapy, and intravitreal injections) add to routine exams under anesthesia (EUA). This information would be useful for planning operating room schedules, staff schedules, family expectations, and billing. Methods: A retrospective, single-center, Institutional Review Board (IRB) approved review of anesthesia duration for retinoblastoma children undergoing EUA with laser, cryotherapy, or intravitreal injections performed at MSK between January 2019 and November 2023. Results: Three hundred eight patients had 2,399 EUAs. The average EUA lasted 24.3 min (range 7-77 min) when no interventions were done. Laser photocoagulation added an average of 18.9 min (range 19-77 min), cryotherapy 26.1 min (range 27-75 min), and intravitreal injection 23.5 min (range 10-71 min) to the basic EUA time. Bilateral laser treatments took 8 min longer than unilateral treatments. Conclusion: EUAs for children with retinoblastoma can be performed relatively quickly. Interventions such as laser, cryotherapy, or intravitreal injections roughly double the time under anesthesia but in some cases can take much longer (>1 h).

Improved method of dilating pupils for ophthalmic exams under anesthesia (faster and easier).

Objective: The pupils of children with retinoblastoma are routinely dilated pre-procedure with Tropicamide and Phenylephrine. Despite that, the pupil constricts once general anesthesia begins. The aim of this study is to see if adding Ketorolac to the regular dilating drops given pre-procedure shortens the length of anesthesia. Methods: Retrospective comparison of time under anesthesia for two groups of retinoblastoma children receiving anesthesia for examination under anesthesia: one group (January 1, 2019 to October 1, 2022) had been dilated with Tropicamide 1% and Phenylephrine 2.5% while the second group (October 2, 2022 to July 1, 2023) was dilated with a combination drop using those drugs with topical Ketorolac 0.5% and Proparacaine 0.5%. Results: Average anesthesia time for patients who received the older two-drug combination was 25 minutes vs. 16 minutes (36% reduction in exposure time) for those who received the newer four-drug combination (9 minutes less anesthesia) (P < 0.001). Conclusions: The use of a combined dilating drop that incorporated Tropicamide 1%, Phenylephrine 2.5%, Proparacaine 0.5% and Ketorolac 0.5% significantly shortened the time for exams under anesthesia for children with retinoblastoma because the pupil remained dilated after anesthesia induction with Sevoflurane. Using this combined drop, children will receive 5-10 hours less anesthesia during their treatment for retinoblastoma and staff will have more than 150 hours of fewer exposure to anesthetic gasses. In addition, far fewer drops are necessary pre-anesthesia, minimizing trauma to the children and families.

Liver cancer initiation requires translational activation by an oncofetal regulon involving LIN28 proteins.

It is unknown which posttranscriptional regulatory mechanisms are required for oncogenic competence. Here, we show that the LIN28 family of RNA-binding proteins (RBPs), which facilitate posttranscriptional RNA metabolism within ribonucleoprotein networks, is essential for the initiation of diverse oncotypes of hepatocellular carcinoma (HCC). In HCC models driven by NRASG12V/Tp53, CTNNB1/YAP/Tp53, or AKT/Tp53, mice without Lin28a and Lin28b were markedly impaired in cancer initiation. We biochemically defined an oncofetal regulon of 15 factors connected to LIN28 through direct mRNA and protein interactions. Interestingly, all were RBPs and only 1 of 15 was a Let-7 target. Polysome profiling and reporter assays showed that LIN28B directly increased the translation of 8 of these 15 RBPs. As expected, overexpression of LIN28B and IGFBP1-3 was able to genetically rescue cancer initiation. Using this platform to probe components downstream of LIN28, we found that 8 target RBPs were able to restore NRASG12V/Tp53 cancer formation in Lin28a/Lin28b-deficient mice. Furthermore, these LIN28B targets promote cancer initiation through an increase in protein synthesis. LIN28B, central to an RNP regulon that increases translation of RBPs, is important for tumor initiation in the liver.

Targeting the synthetic lethal relationship between FOCAD and TUT7 represents a potential therapeutic opportunity for TUT4/7 small molecule inhibitors in cancer.

Targeting synthetic lethal interactions between genes has emerged as a promising strategy for cancer therapy. This study explores the intricate interplay between terminal uridyltransferase 4 (TUT4) and terminal uridyltransferase 7 (TUT7), the 3'-5' exoribonuclease DIS3L2, and the SKI complex-interacting factor Focadhesin (FOCAD) in the context of cancer vulnerability. Using CRISPR and public functional genomics data, we show impairment of cell proliferation upon knockout of TUT7 or DIS3L2, but not TUT4, on cancer cells with FOCAD loss. Moreover, we report the characterization of the first potent and selective TUT4/7 inhibitors that substantially reduce uridylation and demonstrate in vitro and in vivo antiproliferative activity specifically in FOCAD-deleted cancer. FOCAD deficiency post-transcriptionally disrupts the stability of the SKI complex, whose role is to safeguard cells against aberrant RNA. Re-introduction of FOCAD restores the SKI complex and makes these cells less sensitive to TUT4/7 inhibitors, indicating that TUT7 dependency is FOCAD loss-driven. We propose a model where, in absence of FOCAD, TUT7 and DIS3L2 function as a salvage mechanism that degrades aberrant RNA, and genetic or pharmacological inhibition of this pathway leads to cell death. Our findings underscore the significance of FOCAD loss as a genetic driver of TUT7 vulnerability and provide insights into the potential utility of TUT4/7 inhibitors for cancer treatment.

Npt2b deletion attenuates hyperphosphatemia associated with CKD.

The incidence of cardiovascular events and mortality strongly correlates with serum phosphate in individuals with CKD. The Npt2b transporter contributes to maintaining phosphate homeostasis in the setting of normal renal function, but its role in CKD-associated hyperphosphatemia is not well understood. Here, we used adenine to induce uremia in both Npt2b-deficient and wild-type mice. Compared with wild-type uremic mice, Npt2b-deficient uremic mice had significantly lower levels of serum phosphate and attenuation of FGF23. Treating Npt2b-deficient mice with the phosphate binder sevelamer carbonate further reduced serum phosphate levels. Uremic mice exhibited high turnover renal osteodystrophy; treatment with sevelamer significantly decreased the number of osteoclasts and the rate of mineral apposition in Npt2b-deficient mice, but sevelamer did not affect bone formation and rate of mineral apposition in wild-type mice. Taken together, these data suggest that targeting Npt2b in addition to using dietary phosphorus binders may be a therapeutic approach to modulate serum phosphate in CKD.

Calcium mediates glomerular filtration through calcineurin and mTORC2/Akt signaling.

Alterations to the structure of the glomerular filtration barrier lead to effacement of podocyte foot processes, leakage of albumin, and the development of proteinuria. To better understand the signaling pathways involved in the response of the glomerular filtration barrier to injury, we studied freshly isolated rat glomeruli, which allows for the monitoring and pharmacologic manipulation of early signaling events. Administration of protamine sulfate rapidly damaged the isolated glomeruli, resulting in foot process effacement and albumin leakage. Inhibition of calcium channels and chelation of extracellular calcium reduced protamine sulfate-induced damage, suggesting that calcium signaling plays a critical role in the initial stages of glomerular injury. Calcineurin inhibitors (FK506 and cyclosporine A) and the cathepsin L inhibitor E64 all inhibited protamine sulfate-mediated barrier changes, which suggests that calcium signaling acts, in part, through calcineurin- and cathepsin L-dependent cleavage of synaptopodin, a regulator of actin dynamics. The mTOR inhibitor rapamycin also protected glomeruli, demonstrating that calcium signaling has additional calcineurin-independent components. Furthermore, activation of Akt through mTOR had a direct role on glomerular barrier integrity, and activation of calcium channels mediated this process, likely independent of phosphoinositide 3-kinase. Taken together, these results demonstrate the importance of calcium and related signaling pathways in the structure and function of the glomerular filtration barrier.

Repression of osteocyte Wnt/ß-catenin signaling is an early event in the progression of renal osteodystrophy.

Chronic kidney disease-mineral bone disorder (CKD-MBD) is defined by abnormalities in mineral and hormone metabolism, bone histomorphometric changes, and/or the presence of soft-tissue calcification. Emerging evidence suggests that features of CKD-MBD may occur early in disease progression and are associated with changes in osteocyte function. To identify early changes in bone, we utilized the jck mouse, a genetic model of polycystic kidney disease that exhibits progressive renal disease. At 6 weeks of age, jck mice have normal renal function and no evidence of bone disease but exhibit continual decline in renal function and death by 20 weeks of age, when approximately 40% to 60% of them have vascular calcification. Temporal changes in serum parameters were identified in jck relative to wild-type mice from 6 through 18 weeks of age and were subsequently shown to largely mirror serum changes commonly associated with clinical CKD-MBD. Bone histomorphometry revealed progressive changes associated with increased osteoclast activity and elevated bone formation relative to wild-type mice. To capture the early molecular and cellular events in the progression of CKD-MBD we examined cell-specific pathways associated with bone remodeling at the protein and/or gene expression level. Importantly, a steady increase in the number of cells expressing phosphor-Ser33/37-ß-catenin was observed both in mouse and human bones. Overall repression of Wnt/ß-catenin signaling within osteocytes occurred in conjunction with increased expression of Wnt antagonists (SOST and sFRP4) and genes associated with osteoclast activity, including receptor activator of NF-κB ligand (RANKL). The resulting increase in the RANKL/osteoprotegerin (OPG) ratio correlated with increased osteoclast activity. In late-stage disease, an apparent repression of genes associated with osteoblast function was observed. These data confirm that jck mice develop progressive biochemical changes in CKD-MBD and suggest that repression of the Wnt/ß-catenin pathway is involved in the pathogenesis of renal osteodystrophy.

Patterning the embryonic kidney: BMP signaling mediates the differentiation of the pronephric tubules and duct in Xenopus laevis.

The Bone morphogenetic proteins (BMPs) mediate a wide range of diverse cellular behaviors throughout development. Previous studies implicated an important role for BMP signaling during the differentiation of the definitive mammalian kidney, the metanephros. In order to examine whether BMP signaling also plays an important role during the patterning of earlier renal systems, we examined the development of the earliest nephric system, the pronephros. Using the amphibian model system Xenopus laevis, in combination with reagents designed to inhibit BMP signaling during specific stages of nephric development, we revealed an evolutionarily conserved role for this signaling pathway during renal morphogenesis. Our results demonstrate that conditional BMP inhibition after specification of the pronephric anlagen is completed, but prior to the onset of morphogenesis and differentiation of renal tissues, results in the severe malformation of both the pronephric duct and tubules. Importantly, the effects of BMP signaling on the developing nephron during this developmental window are specific, only affecting the developing duct and tubules, but not the glomus. These data, combined with previous studies examining metanephric development in mice, provide further support that BMP functions to mediate morphogenesis of the specified renal field during vertebrate embryogenesis. Specifically, BMP signaling is required for the differentiation of two types of nephric structures, the pronephric tubules and duct.