Objective Injured tubular reabsorption is highlighted as one of the causes of increased
albuminuria in the early stage of
diabetic nephropathy; however, the underlying mechanism has not been fully elucidated. In this study, we aimed to explore whether reducing
inflammation and remodeling the
insulin signaling pathway could improve
albumin uptake of renal tubules. Methods 8-week-old male db/db mice (n=8), a type 2
diabetic nephropathy model, administered with
nuclear factor kappa-B (NF-κB) inhibitor
parthenolide (PTN, 1 mg/kg) intraperitoneally every other day for 8 weeks, were as the treatment group. Meanwhile, the age-matched male db/m mice (n=5) and db/db mice (n=8) were treated with saline as the control group and type 2
diabetic nephropathy group. When the mice were sacrificed, blood and urine were collected to examine homeostasis model assessment of
insulin resistance (HOMA-IR) and urine
albumin creatinine ratio, and kidney samples were used to analyze histopathologic changes with
periodic acid-Schiff (PAS) staining, NF-κB p65, phosphorylation of AKT (p-AKT), amnionless and
cubilin expressions with immunohistochemistry as well as western blot, and the
albumin uptake of renal tubules by using immunofluorescence. In addition, HKC cells were divided into the
insulin group treated with
insulin alone, the TNF-α group treated with
insulin and
tumor necrosis factor (TNF-α), and the TNF-α+PTN group exposed to PTN,
insulin and TNF-α. The levels of
albumin uptake and expression levels of NF-κB p65, p-IRS-1/IRS-1, p-AKT/AKT, amnionless and
cubilin in HKC cells were measured. Results Compared with the db/db group, the db/db+PTN group demonstrated decreased levels of HOMA-IR (36.83±14.09 vs. 31.07±28.05) and urine
albumin creatinine ratio (190.3±7.3 vs. 143.0±97.6 mg/mmol); however, the differences were not statistically significant (P>0.05).
Periodic acid-Schiff staining showed PTN could alleviate the glomerular
hypertrophy and reduce the matrix in mesangial areas of db/db mice. The renal expression of NF-κB p65 was increased and p-AKT (s473) decreased in the db/db group compared with the db/m group (P<0.05). PTN significantly reduced the renal expression of NF-κB p65 and ameliorated the decline of p-AKT (s473) compared with the db/db group (P<0.05). Compared with the db/m group, the expression of amnionless and
cubilin decreased and
albumin uptake in tubules were reduced in the db/db group (P<0.05), and PTN could significantly increase the expression of
cubilin (P<0.05), and improve
albumin uptake in tubules.
Insulin promoted
albumin uptake and the expression of amnionless and
cubilin in HKC cells (P<0.05). TNF-α stimulated the expression of NF-κB p65, increased p-IRS-1 (s307) and reduced p-AKT (s473) in HKC cells (P<0.05). In the TNF-α+PTN group, the expression of NF-κB p65 declined and p-IRS-1 (s307) and p-AKT (s473) were restored, compared with the TNF-α group (P<0.05). The expression of amnionless and
cubilin decreased in the TNF-α group (P<0.05), and PTN could significantly increase the expression of
cubilin (P<0.05). Conclusions
Inflammation caused damage to
insulin signaling, which reduced amnionless-
cubilin expression and
albumin uptake. PTN could reduce
inflammation and remodel the impaired
insulin signaling pathway, which promoted the expression of
cubilin and
albumin uptake. Our study can shed light on the role of
inflammation in the reduction of
albumin uptake of renal tubules in type 2
diabetic nephropathy.