Maria Bernadette Che Ying Chow Vedat O. Yildiz Laura Biederman Alana Dasgupta Anjali Satoskar Aaron Chow Tibor Nadasdy Sergey BRODSKY ^*

• Ohio State University Hospital, Columbus, United States

Proteins are filtered from the blood through the glomerular filtration barrier. Filtered proteins are reabsorbed by proximal tubular epithelial cells (PTECs), which have been shown to possess the ability to regulate protein reabsorption. Histologically, these reabsorbed proteins are seen as tubular protein reabsorption droplets (TPRDs). Experimental studies indicate that PTECs play an important role in regulating proteinuria but the correlations between TPRD and the degree of proteinuria in human kidney biopsies has not been investigated in detail.Consecutive native kidney biopsies with non-proliferative glomerular disease performed at the OSUWMC for a 1-year period were analyzed. Cases with acute glomerular diseases and inadequate biopsies were excluded. The staining intensity of and the percentage of TPRDs, as well as other morphologic parameters are assessed. 109 kidney biopsies were included into the study. A reverse correlation was identified between the percentage of albumin TPRDs and proteinuria (p = 0.047). There are positive correlations between proteinuria and the staining intensity for IgG TPRDs (p = 0.05) and the degree of acute tubular necrosis (ATN) (p = 0.015). In patients with no ATN, positive correlations between proteinuria and albumin and IgG TPRDs were seen, whereas in patients with ATN these correlations were lost. A positive correlation is seen between proteinuria and chronic kidney injury. A strong correlation was noted between the degree of proteinuria and podocyte foot process effacement.Our data indicate that PTECs regulate proteinuria by absorbing proteins from the urine filtrate.Therefore, our study confirms based on the human renal biopsy material that well-functioning renal PTECs play an important role in the regulation of proteinuria.