Cardiac Fibroblast-Dependent Extracellular Matrix Accumulation Is Associated with Diastolic Stiffness in Type 2 Diabetes

Abstract

Cardiovascular complications are a leading cause of death in patients with type 2 diabetes mellitus (T2DM). Diastolic dysfunction is one of the earliest manifestations of diabetes-induced changes in left ventricular (LV) function, and results from a reduced rate of relaxation and increased stiffness. The mechanisms responsible for increased stiffness are not completely understood. Chronic hyperglycemia, advanced glycation endproducts (AGEs), and increased levels of proinflammatory and profibrotic cytokines are molecular pathways known to be involved in regulating extracellular matrix (ECM) synthesis and accumulation resulting in increased LV diastolic stiffness. Experiments were conducted using a genetically-induced mouse model of T2DM generated by a point mutation in the leptin receptor resulting in nonfunctional leptin receptors (db/db murine model). This study correlated changes in LV ECM and stiffness with alterations in basal activation of signaling cascades and expression of profibrotic markers within primary cultures of cardiac fibroblasts from diabetic (db/db) mice with nondiabetic (db/wt) littermates as controls. Primary cultures of cardiac fibrobroblasts were maintained in 25 mM glucose (hyperglycemic-HG; diabetic db/db) media or 5 mM glucose (normoglycemic-NG, nondiabetic db/wt) media. The cells then underwent a 24-hour exposure to their opposite (NG; diabetic db/db) media or 5 mM glucose (HG, nondiabetic db/wt) media. Protein analysis demonstrated significantly increased expression of type I collagen, TIMP-2, TGF-β, PAI-1 and RAGE in diabetic db/db cells as compared to nondiabetic db/wt, independent of glucose media concentration. This pattern of protein expression was associated with increased LV collagen accumulation, myocardial stiffness and LV diastolic dysfunction. Isolated diabetic db/db fibroblasts were phenotypically distinct from nondiabetic db/wt fibroblasts and exhibited a profibrotic phenotype in normoglycemic conditions.

The extracellular matrix in myocardial injury, repair, and remodeling

“…Fibrotic changes in diabetic hearts are, at least in part, independent of coronary artery disease or hypertension (121), reflecting direct effects of metabolic dysregulation on the ECM. Diabetes, obesity, and metabolic dysfunction are associated with activation of cardiac fibroblasts (122) and are accompanied by deposition of matricellular macromolecules (123) and progressive accumulation of fibrillary collagens in the cardiac interstitium (124,125). The molecular basis for activation of the so-called diabetic fibroblast remains unknown.…”

Aortic Stiffness and Interstitial Myocardial Fibrosis by Native T1 Are Independently Associated With Left Ventricular Remodeling in Patients With Dilated Cardiomyopathy

“…[8][9][10] Myocardial dysfunction and remodeling is associated with its pathophysiological hallmark-myocardial fibrosis. [11][12][13][14] Diffuse interstitial or replacement myocardial fibrosis has been demonstrated as a common feature in a broad variety of heart conditions, leading to ventricular remodeling and dilated cardiomyopathy (DCM). 15,16 Cardiovascular magnetic resonance (CMR) can uniquely characterize the extent of replacement fibrosis by late gadolinium enhancement (LGE; Figure 1).…”

Inflammatory and fibrotic responses of cardiac fibroblasts to myocardial damage associated molecular patterns (DAMPs)

“…However, there is evidence for functional expression of TLR2 [57,73], TLR3 [73], TLR4 [68,73,74] and TLR9 [73,75] in CF. Of the known members of the NLR family, CF express NOD1 and NOD2 [26,62], as well as the inflammasome-associated NLRP3 [73,76] RAGE is expressed in several cell types within the heart [64] and in cultured human and rodent CF [23,[77][78][79].…”

“…For example, AGE-modified proteins can induce CF proliferation and collagen production in an angiotensin II-dependent manner [23]. Several recent studies on CF derived from type 2 diabetic patients or diabetic animal models have reported that fibroblasts from diabetic hearts possess an inherent pro-fibrotic phenotype, including elevated collagen synthesis, myofibroblast transdifferentiation and, in some cases, upregulation of RAGE expression [24,78,129,130].…”