Vanderbilt Summer Science Academy

Summer Research Description: High-density lipoproteins (HDL), also known as “good cholesterol”, are best known for their role in carrying cholesterol from peripheral tissues to the liver within the reverse cholesterol transport pathway. In recent years, HDL have been found to carry other molecules, including a wide-variety of proteins, small molecules, and nucleic acids, namely microRNAs (miRNA). miRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression. To establish that HDL participates in a cell-to-cell communication pathway between bone marrow-derived immune cells and the kidney in vivo, we transplanted Mir223-/- (KO) bone marrow into wild-type (WT) C57B/6J recipient mice. Upon transplantation of KO bone marrow into WT mice, there was a significant decrease in HDL-miR-223 levels. Correspondingly, we found a significant decrease in renal miR-223 levels, which resulted in altered renal gene expression. The decrease in miR-223 levels in the kidney resulted in a significant increase in mRNA levels for serpin peptidase inhibitor, clade B (Serpinb8), a predicted miR-223 target. Serpinb8 initiates protein catabolism in cells, and is implicated in kidney inflammation. The reciprocal bone marrow transplant of WT bone marrow into KO mice resulted in an increase in HDL-miR-223 levels in the kidney along with a significant decrease in Serpinb8 mRNA levels. In order to demonstrate miR-223 suppression of SerpinB8 expression, in vitro techniques in multiple kidney cell lines were completed. Overexpression of miR-223 was accomplished by transient-transfection of miR-223 mimetics and miR-223 loss-of-function was achieved by transfection of locked-nucleic acid (LNA) miR-223 inhibitors. Serpinb8 has previously been identified to influence renal inflammation in a kidney regeneration model through the inhibition of the prohormone convertase protein, furin. Furin regulates extracellular matrix proteins and growth factors in the regenerating kidney. We propose that the HDL-miR-223 communication pathway influences kidney inflammation by delivering bone marrow-derived miR-223 to the kidney where it down-regulates the inhibitory Serpinb8, thus increasing serine peptidase activity in the kidney.