These data demonstrate that periostin is a mediator and marker of tubular dedifferentiation and a promising tissue and urine biomarker for kidney injury in experimental models and in clinical renal disease.

Phosphorylated p38 (pp38) mitogen-activated protein kinase (MAPK) regulates heat shock protein 25 (HSP25), stabilizing fibrillar actin (FA) and preventing cleavage to G-actin (GA). Cultured podocytes (Pods) were exposed to glucose (5.5-50 mM)+/-p38MAPK inhibitor SB202190 (SB) or control SB202474 to assess the effects on FA/GA and Pod structure. The relationship of p38MAPK with in vivo Pod structure and albuminuria (Ualb) was assessed in rats with streptozotocin (SZ)-induced diabetes (DM) for 1 week, 1 month, and 4 months. High glucose induced concentration-dependent increases in pp38MAPK and phosphorylated HSP25 (pHSP25) maintained actin cytoskeleton. Inhibition by SB diminished pp38MAPK and pHSP25, decreased FA/GA, and altered FA and GA immunohistochemical appearance. In SZ-DM, glomerular pp38MAPK and biphosphorylated HSP25 were increased after 1 week, declining at 1 month, and at or below C values at 4 months. Glomerular FA/GA in DM was normal at 1 week, declining at 1 month, and low at 4 months. Ualb/creatinine was similar in DM vs C at 1 week, and increased at 1 and 4 months. Morphometry demonstrated progressively diminishing slit pore density in DM over time, denoting evolving effacement. There were strong correlations between slit membrane density and both glomerular biphosphorylated HSP25 and ln Ualb/cr ratio. The data suggest that increased pp38MAPK and pHSP25 comprise an acute adaptation to glycemic stress. Later depletion of DM may contribute to Pod structural alterations and Ualb.

Summary Context Activating antibodies directed at the extracellular calcium‐sensing receptor (CaSR) have been described in autoimmune hypoparathyroidism in the setting of isolated hypoparathyroidism or autoimmune polyglandular syndrome type 1. Materials and Methods A 34‐year‐old female presented with hypocalcaemia (6.0 mg/dL) and hypomagnesaemia (1.1 mg/dL) accompanied by low serum PTH (2.4 pg/mL) as well as urinary calcium and magnesium wasting. She was diagnosed with hypoparathyroidism, which was refractory to standard therapy. She was started on 60 mg prednisone and 150 mg azathioprine treatment daily on suspicion of an autoimmune aetiology. The patient was tested for CaSR antibodies. Results The patient was positive for CaSR antibodies of the IgG1 subtype, which stimulated phosphorylation of extracellular signal‐regulated kinases 1 and 2 (ERK1/2) and inositol phosphate (IP) accumulation. Post‐treatment with prednisone and azathioprine, her serum calcium and magnesium normalized, as did her CaSR antibody titre and antibody‐mediated stimulation of ERK1/2 phosphorylation and IP accumulation. Conclusion This is the first demonstration of CaSR antibody‐mediated hypoparathyroidism responsive to immunosuppressive therapy, adding to the evidence that autoimmune hypoparathyroidism can be, in some cases, reversible and not the result of autoimmune parathyroid destruction.

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