Abstract
Podocyte injury and endoplasmic reticulum (ER) stress have been implicated in the pathogenesis of various glomerular diseases. ERdj3 (DNAJB11) and mesencephalic astrocyte-derived neurotrophic factor (MANF) are ER chaperones lacking the KDEL motif, and may be secreted extracellularly. Since podocytes reside in the urinary space, we examined if podocyte injury is associated with secretion of KDEL-free ER chaperones from these cells into the urine, and if chaperones in the urine reflect ER stress in glomerulonephritis. In cultured podocytes, ER stress increased ERdj3 and MANF intracellularly and in culture medium, whereas GRP94 (KDEL chaperone) increased only intracellularly. ERdj3 and MANF secretion was blocked by the secretory trafficking inhibitor, brefeldin A. Urinary ERdj3 and MANF increased in rats injected with tunicamycin (in the absence of proteinuria). After induction of passive Heymann nephritis (PHN) and puromycin aminonucleoside nephrosis (PAN), there was an increase in glomerular ER stress, and appearance of ERdj3 and MANF in the urine, coinciding with the onset of proteinuria. Rats with PHN were treated with the chemical chaperone, 4-phenyl butyrate (PBA), starting at the time of disease induction, or after disease was established. In both protocols, 4-PBA reduced proteinuria and urinary ER chaperone secretion, compared with PHN rats treated with saline (control). In conclusion, urinary ERdj3 and MANF reflect glomerular ER stress. 4-PBA protected against complement-mediated podocyte injury and the therapeutic response could be monitored by urinary ERdj3 and MANF.