A nanoparticle that reduced levels of the inflammatory protein STING lessened kidney injury in miniature tissue models and mice
A nanoparticle that reduced levels of the inflammatory protein STING lessened kidney injury in miniature tissue models and mice
An article published on 6 September described a lipid nanoparticle with three components: cerium oxide, a plasmid carrying the CasRx system, and the D4F peptide, which helped the particle accumulate in the kidney and bind to macrophages. In kidney organoids (miniature tissue models) and a mouse model of temporarily interrupted blood flow, this formulation reduced macrophage inflammation, tubular injury, and markers of impaired kidney function.
When blood flow to the kidney is temporarily blocked and then restored, cells in the kidney tubules, the small tubes where urine forms, experience oxygen deprivation. Oxidative stress increases in these cells as chemically reactive compounds called reactive oxygen species cause damage. Damaged cells release danger signals. Macrophages, a type of immune cell, respond with inflammation, and their signals can further damage the tubules. STING, a protein involved in innate immunity, is activated when mitochondrial DNA escapes from damaged cells.
The authors combined three ways of acting on this sequence in a single particle. Cerium oxide scavenges excess reactive oxygen species. The plasmid instructs the cell to produce CasRx, a protein that uses a short guide RNA to locate STING RNA and reduce its abundance. The D4F peptide helped the particle accumulate in the kidney and bind to macrophages.
The authors tested whether the result depended on a single guide RNA sequence. In activated mouse macrophages, the complete formulation reduced the proportion of cells with a fluorescent signal indicating reactive oxygen species from 71,9% to 24,5%. A second guide RNA sequence also reduced STING and its downstream signaling. When the researchers used STING RNA with an altered region that the guide RNA could no longer recognize, STING levels and downstream signaling were partially restored. These controls link the effect to CasRx targeting STING.
The authors transferred culture medium from macrophages to tubular cells to test communication between the two cell types. The particles did not reach the tubular cells in this experiment. Medium from macrophages treated with the complete formulation reduced tubular cell death, the reactive oxygen species signal, and inflammatory gene activity. This experiment showed that changes in macrophage state can affect tubular cells through substances the macrophages release into the medium.
In kidney organoids, D4F increased the proportion of cells carrying the particle label from 9,65% to 27,5%. In the mouse model, two intravenous doses were given, one two hours before the kidney blood vessels were clamped and the other 30 minutes after blood flow was restored; the kidneys were assessed after one day. Animals receiving the complete formulation had the lowest tubular injury, creatinine, and urea nitrogen levels among the groups compared. Analysis of gene and protein activity in the tissue showed lower inflammatory pathway activity and greater activity in systems associated with protection against oxidative stress and tissue repair.