The vitamin D analog ZK191784 normalizes decreased bone matrix mineralization in mice lacking the calcium channel TRPV5

The 1α,25(OH)2D3 Analogs ZK159222 and ZK191784 Show Anti-Inflammatory Properties in Macrophage-Induced Preadipocytes via Modulating the NF-κB and MAPK Signaling

PURPOSE

Key research findings suggest that attenuating metaflammation in adipose tissue might be a strategic step to prevent the metabolic syndrome and its associated disease outcomes. The anti-inflammatory effects of 1α,25(OH)₂D₃ have been confirmed in our previous studies, but adverse effects induced at high concentrations restrict its potential clinical translation. Two synthetic 1α,25(OH)₂D₃ analogs ZK159222 and ZK191784 have manifested promising tissue-specific immunomodulatory actions, but limited data are available on adipose tissue. Hence, in this study, we investigated whether ZK159222 and ZK191784 act on preadipocytes or macrophages to attenuate metaflammatory responses via modulating inflammatory and metabolic signaling in macrophage-induced preadipocytes.

METHODS

Preadipocyte-specific effects of ZK159222 and ZK191784 on macrophage-induced preadipocytes were tested by pre-incubating and incubating preadipocytes with the analogs and MacCM. Separately, macrophage-specific effects of both analogs on macrophage-induced preadipocytes were tested by incubating preadipocytes with analog-MacCM or MacCM. The effects of 1α,25(OH)₂D₃ were also examined and set as the positive control. Metaflammatory responses were determined as the concentrations and gene expression of major pro-inflammatory cytokines including IL-1β, IL-6, IL-8, MCP-1 and RANTES, measured using ELISA and qPCR. Inflammatory and metabolic signaling including NF-κB and MAPK were probed using Western blotting.

RESULTS

ZK159222 and ZK191784 act on preadipocytes and macrophages to decrease the secretion and gene expression of the major pro-inflammatory cytokines in macrophage-induced preadipocytes. The anti-inflammatory effects were at least as potent as 1α,25(OH)₂D₃, and no preadipocyte apoptosis was induced at high concentrations. In addition, mostly at high concentrations, both analogs moderately decreased the phosphorylation of relA, p44/42 and p38 MAPK in macrophage-induced preadipocytes.

CONCLUSION

ZK159222 and ZK191784 act on macrophages and preadipocytes to attenuate metaflammatory responses in macrophage-induced preadipocytes, by decreasing phosphorylation of relA/NF-κB, p44/42 and p38 MAPK.

Inhibitors for the Vitamin D Receptor-Coregulator Interaction

The vitamin D receptor (VDR) belongs to the superfamily of nuclear receptors and is activated by the endogenous ligand 1,25-dihydroxyvitamin D3. The genomic effects mediated by VDR consist of the activation and repression of gene transcription, which includes the formation of multiprotein complexes with coregulator proteins. Coregulators bind many nuclear receptors and can be categorized according to their role as coactivators (gene activation) or corepressors (gene repression). Herein, different approaches to develop compounds that modulate the interaction between VDR and coregulators are summarized. This includes coregulator peptides that were identified by creating phage display libraries. Subsequent modification of these peptides including the introduction of a tether or nonhydrolyzable bonds resulted in the first direct VDR-coregulator inhibitors. Later, small molecules that inhibit VDR-coregulator inhibitors were identified using rational drug design and high-throughput screening. Early on, allosteric inhibition of VDR-coregulator interactions was achieved with VDR antagonists that change the conformation of VDR and modulate the interactions with coregulators. A detailed discussion of their dual agonist/antagonist effects is given as well as a summary of their biological effects in cell-based assays and in vivo studies.

TRPV5: a Ca(2+) channel for the fine-tuning of Ca(2+) reabsorption

TRPV5 is one of the two channels in the TRPV family that exhibit high selectivity to Ca(2+) ions. TRPV5 mediates Ca(2+) influx into cells as the first step to transport Ca(2+) across epithelia. The specialized distribution in the distal tubule of the kidney positions TRPV5 as a key player in Ca(2+) reabsorption. The responsiveness in expression and/or activity of TRPV5 to hormones such as 1,25-dihydroxyvitamin D3, parathyroid hormone, estrogen, and testosterone makes TRPV5 suitable for its role in the fine-tuning of Ca(2+) reabsorption. This role is further optimized by the modulation of TRPV5 trafficking and activity via its binding partners; co-expressed proteins; tubular factors such as calbindin-D28k, calmodulin, klotho, uromodulin, and plasmin; extracellular and intracellular factors such as proton, Mg(2+), Ca(2+), and phosphatidylinositol-4,5-bisphosphate; and fluid flow. These regulations allow TRPV5 to adjust its overall activity in response to the body's demand for Ca(2+) and to prevent kidney stone formation. A point mutation in mouse Trpv5 gene leads to hypercalciuria similar to Trpv5 knockout mice, suggesting a possible role of TRPV5 in hypercalciuric disorders in humans. In addition, the single nucleotide polymorphisms in Trpv5 gene prevalently present in African descents may contribute to the efficient renal Ca(2+) reabsorption among African descendants. TRPV5 represents a potential therapeutic target for disorders with altered Ca(2+) homeostasis.