Project Summary: The spontaneously hypertensive rat (SHR) line, SHR-A3, is susceptible to hypertensive renal injury, while other SHR lines, including SHR-B2, share similar levels of hypertension, but resist injury. These two inbred SHR lines are both progeny of the same founding pair of rats and have different ancestry at only 13% of their genomes. We have studied the development of hypertensive renal injury in this model and observed its emergence in young adult animals and its progression to moderately severe levels that cause increased serum creatinine levels at 40 weeks of age. Histological analysis indicates extensive infiltration of immune cells into the kidney concurrent with development of injury. We have demonstrated that pharmacological immunosuppression prevents hypertensive renal injury and we have linked disease to functional genetic variation in genes involved in the immune response and its regulation. We have recently acquired very high quality whole genome sequence for our hypertensive renal injury prone and resistant rats. This has uncovered extreme genetic variation in the immunoglobulin heavy chain locus, an ~8Mb segment of the genome that is essential for B lymphocyte-mediated immunity and which our SHR lines have inherited from different ancestors. The genetic variation endows SHR-A3 with a pre-immune immunoglobulin repertoire that is very different from SHR-B2. Indeed, >17% of all genomic amino acid coding difference between our injury resistant and susceptible SHR lines occurs in this locus, even though it accounts for just 0.3% of the genome. We have attached function to this genetic variation including: immunoglobulin abundance in serum and; receptor binding of the Fc region of immunoglobulin. This repertoire difference may alter the recognition of neo-antigens that are present as renal injury emerges. We have also uncovered a recent single nucleotide mutation creating immune deficiency by disrupting immune regulation. The affected gene, Stim1, is the key regulator of store-operated calcium entry (SOCE). This signal links depletion of ER calcium stores to generation of a persistent calcium signal generated by Stim1 gating of extracellular calcium entry and is vital for normal T lymphocyte function. Stim1 possesses a truncation mutation in SHR-A3 and the truncated protein suffers loss of key functional residues in the C-terminal that incompletely suppresses Stim1 calcium signaling function. Using backcrossing to permit congenic line creation (in which loci containing these variations are transferred from injury-resistant SHR-B2 into the SHR-A3 genetic background) we have developed evidence that hypertensive renal injury susceptibility arises from differences in the immune response arising from these loci. The initiating damage to the kidney caused by hypertension arises from the breakdown of auto-regulation of renal blood flow as elevated blood pressure exceeds the range across which this regulation can operate. We have identified an additional locus that increases the likelihood that blood pressure in SHR-A3 will exceed the auto-regulatory threshold. The chief hypothesis our proposal will test is that these three loci account for the difference in susceptibility to renal injury between SHR-A3 and SHR-B2. We further hypothesize that it is the effect of these mutations within the immune system that drive renal injury and we will attempt to prove the tissue specificity of disease pathogenesis by transfer of immune cells from SHR-B2 to SHR-A3. Finally, studies of immune dysfunction attributable to Stim1 mutation indicate that loss of T cell function, including the role of T helper cells to guide B lymphocyte maturation and of T regulatory cells to control B lymphocyte proliferation, leads to a disease process that amplifies auto-antibody production. Development of renal injury may be attenuated by specific interventions to alter B cell mediated auto-antibody induced immunity and we propose experiments to test this hypothesis.

R01DK114235

2017-09-01

2021-05-31