Rat and mouse models of diabetic nephropathy showed that OPN was highly expressed in the tubular epithelium of the renal cortex and glomeruli [44]; this was associated with extensive macrophage accumulation in the kidney interstitium, indicating that OPN upregulation and macrophage recruitment may have roles in tubulointerstitial injury in diabetic nephropathy. Here, SPP1 is linked to diabetic kidney disease.