Proteasome inhibition reduces plasma cell and antibody secretion, but not angiotensin II-induced hypertension

IntroductionDepletion of mature B cells affords protection against experimental hypertension. However, whether B cell-mediated hypertension is dependent on differentiation into antibody-secreting cells (ASCs) remains unclear. Using the proteasome inhibitor, bortezomib, the present study tested the effect of ASC reduction on angiotensin II-induced hypertension. MethodsMale C57BL6/J mice were infused with angiotensin II (0.7 mg/kg/day; s.c.) for 28 days via osmotic minipump to induce hypertension. Normotensive control mice received saline infusion. Bortezomib (750 mu g/kg) or vehicle (0.1% DMSO) was administered (i.v.) 3 days prior to minipump implantation, and twice weekly thereafter. Systolic blood pressure was measured weekly using tail-cuff plethysmography. Spleen and bone marrow B1 (CD19(+)B220(-)), B2 (B220(+)CD19(+)) and ASCs (CD138(hi)Sca-1(+)Blimp-1(+)) were enumerated by flow cytometry. Serum immunoglobulins were quantified using a bead-based immunoassay. ResultsBortezomib treatment reduced splenic ASCs by similar to 68% and similar to 64% compared to vehicle treatment in normotensive (2.00 +/- 0.30 vs. 0.64 +/- 0.15 x 10(5) cells; n = 10-11) and hypertensive mice (0.52 +/- 0.11 vs. 0.14 +/- 0.02 x 10(5) cells; n = 9-11), respectively. Bone marrow ASCs were also reduced by bortezomib in both normotensive (4.75 +/- 1.53 vs. 1.71 +/- 0.41 x 10(3) cells; n = 9-11) and hypertensive mice (4.12 +/- 0.82 vs. 0.89 +/- 0.18 x 10(3) cells; n = 9-11). Consistent with ASC reductions, bortezomib reduced serum IgM and IgG2a in all mice. Despite these reductions in ASCs and antibody levels, bortezomib did not affect angiotensin II-induced hypertension over 28 days (vehicle: 182 +/- 4 mmHg vs. bortezomib: 177 +/- 7 mmHg; n = 9-11). ConclusionReductions in ASCs and circulating IgG2a and IgM did not ameliorate experimental hypertension, suggesting other immunoglobulin isotypes or B cell effector functions may promote angiotensin II-induced hypertension.