Altered cellular compartmentalization as a potential pathomechanism driving CKD.

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Genetic mutations in proteins of the nuclear pore complex (NPC) recently identified by Antonin cause podocytopathy and podocyte loss in humans, resulting in focal and segmental glomerulosclerosis (FSGS) and chronic kidney disease (CKD). NPCs regulate the essential transport nucleoplasm and cytoplasm and hence the distribution of proteins between these compartments. In neurons, this protein distribution is impaired when NPCs are mutated, but this also occurs in disease and during physiological aging. The podocyte is a critical cell in the kidney, which cannot be replaced and cannot divide - similar to neurons. In most glomerular diseases as well as in physiological aging, podocytes are lost for yet unknown reasons. Here, we will explore whether an insufficient or impaired NPC function leading to protein mislocalization is associated with the loss of podocytes in physiological aging and in glomerular disease. For this we will1.) test the value of nuclear-cytoplasmic protein ratio (NCR) as diagnostic tool. We will examine by immunostainings the distribution of known nuclear and cytoplasmic marker proteins in podocytes in aged mice and in a rat strain with a genetic form of FSGS as well as in human biopsies. 2.) isolate podocytes from transgenic mice to analyze the subcellular proteomes to identify novel proteins with an impaired nuclear to cytoplasmic ratio in aging or glomerular disease. 3.) develop methods to manipulate protein distribution between the nucleus and cytoplasm in established in-vitro assays in primary podocytes and restore defective nuclear/cytoplasmic compartmentalization. 4.) test in rat and mouse models whether these manipulations can ameliorate disease progression and prevent CKD. 5.) examine a potential role of the NCR and loss of compartmentalization also in the tubular compartment of the kidney, specifically in proximal tubular cells of aging mice as well as in acute kidney injury.In conclusion, we will analyze the relevance of a novel pathomechanism of an impaired NPC permeability recently identified in podocytes, which phenotypically results in progressive podocyte loss and subsequent FSGS. We will investigate its diagnostic utility, its relevance for phase transition to CKD in physiological aging and acute kidney injury and aim for the first pharmacological interventions in mouse and rat models.