Kidney Week

Abstract: FR-PO147

Kidney Injury Molecule-1 (KIM-1) Mediates the Proximal Tubule Uptake of Free Fatty Acids (FFA) Resulting in Mitochondrial Injury and the DNA Damage Response (DDR)

Session Information

• Mitochondriacs and More
  November 03, 2017 | Location: Hall H, Morial Convention Center
  Abstract Time: 10:00 AM - 10:00 AM

Category: Diabetes

• 501 Diabetes Mellitus and Obesity: Basic - Experimental

Authors

• Mori, Yutaro, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States

Yutaro Mori,

• Galichon, Pierre, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States

Pierre Galichon,

• Brooks, Craig R., Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States

Craig R. Brooks,

• Ichimura, Takaharu, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States

Takaharu Ichimura,

• Bonventre, Joseph V., Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States

Joseph V. Bonventre,

Background

KIM-1 is the most upregulated proximal tubule protein in kidney injury. KIM-1 mediates the uptake of apoptotic cells and oxidized low-density lipoproteins (oxLDL). Deregulation of lipid metabolism during diabetes causes disturbed FFA metabolism which is implicated in injurious effects on the kidney in diabetic nephropathy (DN).

Methods

Renal epithelial cells expressing KIM-1 (KIM-1-PK1) were exposed to the FFA palmitic acid, and FFA uptake, necrotic cell death, accumulation of lipids and the DDR were assessed in vitro. Mitochondrial status and lysosomal activation were measured using the MitoTracker and LysoSenser dyes, respectively. Pro-fibrotic factor(s) production by FFA-treated KIM-1-PK1 cells were determined with a fibrosis bioassay using mouse primary baby kidney fibroblasts. Functional knockout of KIM-1 (KIM-1^Δmucin) and control mice were used for electron micrographic assessment of the effects of KIM-1 on mitochondrial fragmentation in diabetic nephropathy.

Results

FFA were taken up in the KIM-1-PK1 cells but not in control pcDNA-PK1 cells. Necrosis was increased after FFA treatment with FFA in KIM-1-PK1 cells when compared to controls. Lipid droplets were formed in the KIM-1 cells. FFA-treated KIM-1-PK1 cells had an increased number of fragmented mitochondria at 48 hr. These mitochondria co-localized with activated lysosomes suggesting mitophagy. Nuclear p-ATM and p-H2AX were increased in FFA-treated KIM-1-PK1 cells but not in the control cells. Conditioned media, harvested from KIM-1-PK1 cells treated with FFA, increased α-smooth muscle actin expression of mouse fibroblasts. oxLDL uptake also induced mitochondrial fragmentation and nuclear p-ATM and p-H2AX in a KIM-1 dependent way. Mitochondrial fragmentation occurred in a streptozotocin model of diabetic nephropathy in wild-type mice but not in KIM-1^Δmucin mice.

Conclusion

KIM-1 mediates the epithelial uptake of FFA, which leads to cell death, lipid accumulation, activation of mitochondrial fragmentation and mitophagy, DDR and fibrosis. Our findings suggest that KIM-1-mediated FFA uptake may play an important role in pathophysiology of the DN.

Funding

• NIDDK Support