Serum amyloid A and Janus kinase 2 in a mouse model of diabetic kidney disease

Abstract

Background Serum amyloid A (SAA), a potent inflammatory mediator, and Janus kinase 2 (JAK2), an intracellular signaling kinase, are increased by diabetes. The aims were to elucidate: 1) a JAK2-mediated pathway for increased SAA in the kidneys of diabetic mice; 2) a JAK2-SAA pathway for inflammation in podocytes. Methods Akita diabetic mice (129S6) with podocyte JAK2 overexpression and angiotensin II infusion (4 weeks) were given a JAK1,2 inhibitor (LY03103801, 3 mg/kg/day orally for the last two weeks). Kidneys were immunostained for SAA isoform 3 (SAA3). SAA3 knockout and control mouse podocytes were exposed to advanced glycation end products (AGE) or exogenous SAA with JAK2 inhibition (Tyrphostin AG 490, 50μM). JAK2 activity (phosphorylation, Western blot, 1 hour) and mRNA for SAA3 and associated inflammatory genes (Cxcl5, Ccl2, and Ccl5) were measured by RT-PCR (20 hours). Results SAA3 protein was present throughout the diabetic kidney, and podocyte JAK2 overexpression increased tubulointerstitial SAA3 compared to wild type diabetic controls, 43% versus 14% (p = 0.007); JAK1,2 inhibition attenuated the increase in SAA3 to 15% (p = 0.003). Urine albumin-to-creatinine ratio (r = 0.49, p = 0.03), mesangial index (r = 0.64, p = 0.001), and glomerulosclerosis score (r = 0.51, p = 0.02) were associated with SAA3 immunostaining scores across mouse groups. Exposing podocytes to AGE or exogenous SAA increased JAK2 activity within one hour and mRNA for associated inflammatory genes after 20 hours. JAK2 inhibition reduced SAA3 mRNA expression in podocytes exposed to AGE or SAA. SAA3 knockout podocytes had >85% lower AGE-induced inflammatory genes. Conclusion JAK1,2 inhibition reduced SAA and histological features of DKD in podocyte JAK2-overexpressing mice. In podocytes exposed to a diabetes-like condition, JAK2 inhibition reduced expression of SAA, while SAA knockout blocked expression of associated pro-inflammatory mediators. SAA may promote JAK2-dependent inflammation in the diabetic kidney.

Pathogenic Pathways and Therapeutic Approaches Targeting Inflammation in Diabetic Nephropathy

“…Selective compounds targeting JAK2 (AG-490/tyrphostin) [269], JAK1/2 (/baricitinib) [270,271], STAT1 (fludarabine) [272] and STAT3 (nifuroxazide, S3I-201) [273] reduced albuminuria, inflammatory infiltrate, renal damage (mesangial expansion, oxidative stress, tubular atrophy, and fibrosis) and serum amyloid A in experimental DN. New design compounds such as the bromodomain inhibitor MS417 have shown the capacity to directly target acetyl-lysine residues of STAT3 and to reduce proteinuria and kidney damage in db/db mice [274].…”

Distribution of serum amyloid A and establishment of reference intervals in healthy adults

“…2 The elevated SAA is closely related to inflammation-mediated diseases, such as liver diseases, autoimmune diseases, metabolism-related diseases, amyloidosis, and tumors. [3][4][5][6] Besides, in acute-phase reactions such as acute inflammation and trauma, the concentration of SAA in the blood can be rapidly increased by approximately 1000-fold within 5-6 hours under the stimulation of IL-1, IL-6, and TNF-α. 7,8 Therefore, SAA has important clinical value in the diagnoses, progression, and prognoses of diseases associated with inflammation.…”

“…Although both SAA and C‐reactive protein (CRP) are acute‐phase proteins, the detection of SAA is more conclusive than the detection of CRP in patients with viral infections, severe acute pancreatitis, and rejection reactions to kidney transplants . The elevated SAA is closely related to inflammation‐mediated diseases, such as liver diseases, autoimmune diseases, metabolism‐related diseases, amyloidosis, and tumors . Besides, in acute‐phase reactions such as acute inflammation and trauma, the concentration of SAA in the blood can be rapidly increased by approximately 1000‐fold within 5‐6 hours under the stimulation of IL‐1, IL‐6, and TNF‐α .…”

Anti-inflammatory, antioxidant and renoprotective effects of SOCS1 mimetic peptide in the BTBR ob/ob mouse model of type 2 diabetes

“…36 Recently, an experimental study conducted in podocyte JAK2-overexpressing Akita mice with angiotensin II infusion demonstrated that the JAK1/2 inhibitors, tyrphostin and baricitinib, reduced proteinuria and glomerular kidney damage. 37 In addition, a phase II trial on baricitinib has shown promise for high-risk patients with diabetic kidney disease. 38 Our early studies have shown effective reduction of renal damage when using different SOCS delivery systems (adenovirus and cell-permeable peptide) in animal models of kidney disease, including T1D.…”