Abstract 105: Maternal Diet Leads to Nephron Count Differences After Postnatal Day 14 and Time-dependent Differences in Apoptosis and Unfolded Protein Response in Dahl Salt-sensitive Rats

Abstract

We have shown that maternal exposure to Casein-based AIN-76A diet [SS/JrHsdMcwi (SS/Mcw) rats] compared to grain-based 5L2F diet [SS/JrHsdMcwiCrl (SS/Crl) rats] during the gestational-lactational period exacerbates the development of salt-induced hypertension and renal injury in adult SS rats. We hypothesized that SS/Mcw rats will have significantly fewer glomeruli than SS/Crl rats, and determined its potential mechanisms. At different time points during development [embryonic day 20 (E 20), day of life (DOL) 14, 21, 56]: glomerular counts were determined by maceration method and by glomerular density (total glomerular number/renal cortex area); apoptosis was measured by TUNEL assay; RT-PCR, Western Blot and immunostaining were used to examine the expression level of genes involved in the apoptotic pathway and unfolded protein response (UPR). We found lower glomerular counts in SS/Mcw compared to SS/Crl rats at DOL 21 [26048±1423 per kidney vs. 34766±1821 (p<0.001] and DOL 56 [15717±2052 vs. 27999±3362 (p <0.001)], and lower glomerular densities [DOL 21, 10.8±1.0/mm2 vs. 13.2±1.6 (p<0.001); DOL 56, 2.4±0.1 vs. 3.6±0.2 (p < 0.001)]. Glomerular density was not different between SS/Mcw and SS/Crl at DOL 14 when nephrogenesis is complete. We found higher glomerular apoptosis in SS/Mcw compared to SS/Crl rats at DOL 14 [9.5±1.4 per 100 glomeruli vs. 5.1±1.8 (p<0.01)] and DOL 21 [5.2±0.7 vs. 3.6±0.5 (p <0.01)]. mRNA levels of several genes involved in intrinsic apoptotic pathway and UPR were significantly upregulated in SS/Mcw rats compared to SS/Crl rats at different time points. Significantly lower UPR-related protein expression in SS/Mcw compared to SS/Crl rats was detected for JNK and GRP78 (DOL 14 and 56) and CHOP (DOL 56). Significantly higher UPR-related protein expression in SS/Mcw compared to SS/Crl rats were detected for GRP78 (E 20), JNK (DOL 21) and Caspase 12 (DOL 14, 21 and 56). Caspase 12 was located in the glomeruli in DOL 21 and 56 kidneys. Our results show marked decrease of glomerular counts with age in SS/Mcw compared to SS/Crl after DOL 14. The time-dependent differences in the expression of apoptosis and UPR-related genes leading to glomerular apoptosis may be a potential mechanism for the nephron count differences between SS/Mcw and SS/Crl.