Miina Öhman

Significance Statement: Although diabetic nephropathy is partly genetic in nature, the underlying pathogenetic mechanisms are obscure. The authors assembled from the homogeneous Finnish population a cohort of 76 sibling pairs with type 1 diabetes who were discordant for diabetic nephropathy. Using whole-genome sequencing and multiple analytic approaches, they identified DNA variants associated with nephropathy or its absence and validated their findings in a 3531-member cohort of unrelated Finns with type 1 diabetes. The genes most strongly associated with diabetic nephropathy encode two protein kinase C isoforms (isoforms ε and ι) not previously implicated in the condition. Besides providing a resource for studies on diabetic complications, these findings support previous hypotheses that the protein kinase C family plays a role in diabetic nephropathy and suggest potential targets for treatment. Background: Several genetic susceptibility loci associated with diabetic nephropathy have been documented, but no causative variants implying novel pathogenetic mechanisms have been elucidated. Methods: We carried out whole-genome sequencing of a discovery cohort of Finnish siblings with type 1 diabetes who were discordant for the presence (case) or absence (control) of diabetic nephropathy. Controls had diabetes without complications for 15–37 years. We analyzed and annotated variants at genome, gene, and single-nucleotide variant levels. We then replicated the associated variants, genes, and regions in a replication cohort from the Finnish Diabetic Nephropathy study that included 3531 unrelated Finns with type 1 diabetes. Results: We observed protein-altering variants and an enrichment of variants in regions associated with the presence or absence of diabetic nephropathy. The replication cohort confirmed variants in both regulatory and protein-coding regions. We also observed that diabetic nephropathy–associated variants, when clustered at the gene level, are enriched in a core protein-interaction network representing proteins essential for podocyte function. These genes include protein kinases (protein kinase C isoforms ε and ι) and protein tyrosine kinase 2. Conclusions: Our comprehensive analysis of a diabetic nephropathy cohort of siblings with type 1 diabetes who were discordant for kidney disease points to variants and genes that are potentially causative or protective for diabetic nephropathy. This includes variants in two isoforms of the protein kinase C family not previously linked to diabetic nephropathy, adding support to previous hypotheses that the protein kinase C family members play a role in diabetic nephropathy and might be attractive therapeutic targets.

Background: The MMP (matrix metalloproteinase) family plays diverse and critical roles in directing vascular wall remodeling in atherosclerosis. Unlike secreted‐type MMP s, a member of the membrane‐type MMP family, MT 1‐ MMP (membrane‐type 1 MMP; MMP 14), mediates pericellular extracellular matrix degradation that is indispensable for maintaining physiological extracellular matrix homeostasis. However, given the premature mortality exhibited by MT 1‐ MMP –null mice, the potential role of the proteinase in atherogenesis remains elusive. We sought to determine the effects of both MT 1‐ MMP heterozygosity and tissue‐specific gene targeting on atherogenesis in APOE (apolipoprotein E)–null mice. Methods and Results: MT 1‐ MMP heterozygosity in the APOE ‐null background ( Mmp14 ^+/− Apoe ^−/− ) significantly promoted atherogenesis relative to Mmp14 ^+/+ Apoe ^−/− mice. Furthermore, the tissue‐specific deletion of MT 1‐ MMP from vascular smooth muscle cells ( VSMC s) in SM 22α‐Cre(+) Mmp14 ^F/F Apoe ^−/− ( VSMC ‐knockout) mice likewise increased the severity of atherosclerotic lesions. Although VSMC ‐knockout mice also developed progressive atherosclerotic aneurysms in their iliac arteries, macrophage‐ and adipose‐specific MT 1‐ MMP –knockout mice did not display this sensitized phenotype. In VSMC ‐knockout mice, atherosclerotic lesions were populated by hyperproliferating VSMC s (smooth muscle actin– and Ki67–double‐positive cells) that were characterized by a proinflammatory gene expression profile. Finally, MT 1‐ MMP –null VSMC s cultured in a 3‐dimensional spheroid model system designed to mimic in vivo–like cell–cell and cell–extracellular matrix interactions, likewise displayed markedly increased proliferative potential. Conclusions: MT 1‐ MMP expressed by VSMC s plays a key role in limiting the progression of atherosclerosis in APOE ‐null mice by regulating proliferative responses and inhibiting the deterioration of VSMC function in atherogenic vascular walls.

Objective—: Lymphatic vessels collect extravasated fluid and proteins from tissues to blood circulation as well as play an essential role in lipid metabolism by taking up intestinal chylomicrons. Previous studies have shown that impairment of lymphatic vessel function causes lymphedema and fat accumulation, but clear connections between arterial pathologies and lymphatic vessels have not been described. Approach and Results—: Two transgenic mouse strains with lymphatic insufficiency (soluble vascular endothelial growth factor 3 [sVEGFR3] and Chy) were crossed with atherosclerotic mice deficient of low-density lipoprotein receptor and apolipoprotein B48 (LDLR ^−/− /ApoB ^100/100 ) to study the effects of insufficient lymphatic vessel transport on lipoprotein metabolism and atherosclerosis. Both sVEGFR3×LDLR ^−/− /ApoB ^100/100 mice and Chy×LDLR ^−/− /ApoB ^100/100 mice had higher plasma cholesterol levels compared with LDLR ^−/− /ApoB ^100/100 control mice during both normal chow diet (16.3 and 13.7 versus 8.2 mmol/L, respectively) and Western-type high-fat diet (eg, after 2 weeks of fat diet, 45.9 and 42.6 versus 30.2 mmol/L, respectively). Cholesterol and triglyceride levels in very-low-density lipoprotein and low-density lipoprotein fractions were increased. Atherosclerotic lesions in young and intermediate cohorts of sVEGFR3×LDLR ^−/− /ApoB ^100/100 mice progressed faster than in control mice (eg, intermediate cohort mice at 6 weeks, 18.3% versus 7.7% of the whole aorta, respectively). In addition, lesions in sVEGFR3×LDLR ^−/− /ApoB ^100/100 mice and Chy×LDLR ^−/− /ApoB ^100/100 mice had much less lymphatic vessels than lesions in control mice (0.33% and 1.07% versus 7.45% of podoplanin-positive vessels, respectively). Conclusions—: We show a novel finding linking impaired lymphatic vessels to lipoprotein metabolism, increased plasma cholesterol levels, and enhanced atherogenesis.