Kidney Week

Abstract: TH-OR31

Spatial Detection and Consequences of Nonkidney Calcitriol Production as Assessed by Targeted Mass Spectrometry Imaging

Session Information

• CKD-MBD and Kidney Stones: Novel Insights
  October 24, 2024 | Location: Room 6D, Convention Center
  Abstract Time: 05:00 PM - 05:10 PM

Category: Bone and Mineral Metabolism

• 501 Bone and Mineral Metabolism: Basic

Authors

• Meyer, Mark B., University of Wisconsin-Madison Department of Nutritional Sciences, Madison, Wisconsin, United States

Mark B. Meyer, PhD

• Lee, Seong Min, University of Wisconsin-Madison Department of Nutritional Sciences, Madison, Wisconsin, United States

Seong Min Lee, PhD

• Cichanski, Shannon R., University of Wisconsin-Madison Department of Nutritional Sciences, Madison, Wisconsin, United States

Shannon R. Cichanski

• Cobice, Diego Federico, Ulster University, Coleraine, United Kingdom

Diego Federico Cobice, PhD

• Pike, J. Wesley, University of Wisconsin-Madison Department of Biochemistry, Madison, Wisconsin, United States

J. Wesley Pike, MS, PhD

Background

The benefits of vitamin D supplementation beyond calcium and phosphate maintenance in humans are highly clinically debated. Kidney expression of CYP27B1 is the source of endocrine 1,25(OH)₂D₃ (active form of vitamin D) that maintains serum calcium and phosphate. 1,25(OH)₂D₃ may also be made by the CYP27B1 enzyme in non-renal cells, like immune cells, in a process driven by cellular availability of precursor 25(OH)D₃ and inflammation. Due to the endocrine nature of renally produced 1,25(OH)₂D₃ in circulation, it is difficult to discern between these two sources.

Methods

We have recently created a regulatory deletion model of Cyp27b1 (M1/M21-DIKO) where the mice have normal inflammatory-regulated Cyp27b1 expression in non-renal tissues (unlike global Cyp27b1-KO), but no expression within the kidney. Using these unique M1/M21-DIKO mice, we hypothesized that vitamin D supplementation will increase 25(OH)D₃ circulation and tissue availability, and therefore increase the production of 1,25(OH)₂D₃ in non-renal tissues. Utilizing on-tissue chemical derivatization (OTCD) and targeted Matrix Assisted Laser Desorption Ionization-Mass Spectrometry Imaging (MALDI-MSI), we investigated the tissue distribution of 1,25(OH)₂D₃ and 25(OH)D₃ in the M1/M21-DIKO mice compared to Cyp27b1-KO mice and wildtype littermates after PBS perfusion in the kidney, liver, spleen, and thymus.

Results

MALDI-MSI demonstrated that the levels of 25(OH)D₃ were greatly affected by vitamin D supplementation and increased in all tissues examined. We confirmed that the M1/M21-DIKO mouse, like the Cyp27b1-KO mouse, had no kidney production of 1,25(OH)₂D₃ even in the animals with high levels of supplementation. However, we saw increased production of 1,25(OH)₂D₃ in tissues outside of the kidney such as the spleen in the M1/M21-DIKO mouse. Gene expression found increased Il4 and decreased Tnfa in the spleen indicating an initiation of an anti-inflammatory program as observed with vitamin D in immune cells ex vivo.

Conclusion

Taken together, these data verify, visualize, and quantify, for the first time, non-renal production of 1,25(OH)₂D₃ in vivo, provide a consequence of non-renal 1,25(OH)₂D₃ production in cytokine changes, and offer a benefit to elevated vitamin D supplementation in potential positive outcomes for inflammatory disease.

Funding

• NIDDK Support