More than tubular dysfunction: cystinosis and kidney outcomes

Renal transplantation for infantile and juvenile cystinosis: Two case report and review of the literature

Cystinosis is a rare autosomal recessive lysosomal storage disorder characterized by cystine buildup in various tissues, including the kidneys. Renal involvement is the primary manifestation, leading to end-stage renal disease (ESRD) if left untreated. Kidney transplantation (KT) in patients with cystinosis has significantly improved their prognosis for the disease outcome. Detailed reports on preoperative and Long-term postoperative management in these patients remain sparse. This report discusses the outcomes of two young adult patients of Middle Eastern descent with cystinosis who underwent KT. The first patient, diagnosed with infantile nephropathic cystinosis treated by cystine-depleting therapy, was operated by KT at the age of 18. The second patient, diagnosed with juvenile cystinosis, underwent transplantation at the age of 35 after being treated with hemodialysis. Our report describes detailed pre- and postoperative managements, including laboratory results, and pharmacological interventions. Both cases highlighted the varying clinical manifestations and disease severity between infantile and juvenile cystinosis. Pre-transplant conditions included renal dysfunction, growth retardation, secondary hyperparathyroidism, anemia, and extrarenal manifestations. Following KT, both patients experienced regained renal function, resolution of extrarenal complications, and normalization of laboratory parameters. Furthermore, both patients showed excellent postoperative outcomes with no acute rejection or allograft-related complications. KT is the treatment of choice for cystinosis patients with ESRD. Long-term follow-up post-transplantation is crucial to maintain good graft function. Further studies may elucidate optimal pre- and postoperative management protocols for this rare condition.

TRPML1-Induced Lysosomal Ca2+ Signals Activate AQP2 Translocation and Water Flux in Renal Collecting Duct Cells

Lysosomes are acidic Ca²⁺ storage organelles that actively generate local Ca²⁺ signaling events to regulate a plethora of cell functions. Here, we characterized lysosomal Ca²⁺ signals in mouse renal collecting duct (CD) cells and we assessed their putative role in aquaporin 2 (AQP2)-dependent water reabsorption. Bafilomycin A1 and ML-SA1 triggered similar Ca²⁺ oscillations, in the absence of extracellular Ca²⁺, by alkalizing the acidic lysosomal pH or activating the lysosomal cation channel mucolipin 1 (TRPML1), respectively. TRPML1-dependent Ca²⁺ signals were blocked either pharmacologically or by lysosomes' osmotic permeabilization, thus indicating these organelles as primary sources of Ca²⁺ release. Lysosome-induced Ca²⁺ oscillations were sustained by endoplasmic reticulum (ER) Ca²⁺ content, while bafilomycin A1 and ML-SA1 did not directly interfere with ER Ca²⁺ homeostasis per se. TRPML1 activation strongly increased AQP2 apical expression and depolymerized the actin cytoskeleton, thereby boosting water flux in response to an hypoosmotic stimulus. These effects were strictly dependent on the activation of the Ca²⁺/calcineurin pathway. Conversely, bafilomycin A1 led to perinuclear accumulation of AQP2 vesicles without affecting water permeability. Overall, lysosomal Ca²⁺ signaling events can be differently decoded to modulate Ca²⁺-dependent cellular functions related to the dock/fusion of AQP2-transporting vesicles in principal cells of the CD.