Summary The hair follicle bulge in the epidermis associates with the arrector pili muscle (APM) that is responsible for piloerection (commonly called "goosebumps"). We show that deposition of nephronectin into the basement membrane by bulge stem cells mediates selective adhesion of α8β1 integrin-expressing mesenchymal cells, including APM progenitors. Nephronectin induces α8 integrin-positive cells to upregulate smooth muscle markers. In nephronectin-null skin, the number of APM is reduced and those that form insert above the bulge, where there is compensatory upregulation of the nephronectin family member EGFL6. Deletion of α8 integrin also abolishes the selectivity of APM anchorage to the bulge. Nephronectin is a Wnt target gene; epidermal β-catenin activation upregulates epidermal nephronectin and dermal α8 integrin expression. We conclude that by expressing nephronectin bulge stem cells provide a smooth muscle cell niche and act as tendon cells for the APM. The results also reveal a functional role for basement membrane heterogeneity in tissue patterning.

Abstract-The (pro)renin receptor [(P)RR], a new component the renin-angiotensin system, was cloned recently. The (P)RR promotes direct mitogen-activated protein kinase signaling and nonproteolytic prorenin activation. We investigated the role of a (P)RR blocker, a peptide consisting of 10 amino acids from the prorenin prosegment called the "handle-region" peptide (HRP), on target organ damage in renovascular hypertensive 2-kidney, 1-clip (2K1C) rats. Vehicle-treated 2K1C rats were compared with HRP-treated 2K1C rats (3.5 g/kg per day) and sham-operated controls. Vehicle-treated 2K1C rats developed hypertension (186Ϯ17 mm Hg), cardiac hypertrophy (3.16Ϯ0.16 mg/g), renal inflammation, fibrosis, vascular, and tubular damage. Chronic HRP treatment did not affect blood pressure (194Ϯ15 mm Hg), cardiac hypertrophy (2.97Ϯ0.11 mg/g), or renal damage. Furthermore, we investigated the renal renin and (P)RR expression. The clipped kidney of 2K1C and HRP-treated 2K1C rats showed a higher renin expression and juxtaglomerular index compared with sham-operated kidneys. The unclipped kidney showed suppressed renin expression. In contrast, (P)RR mRNA expression was not altered in any group. Plasma renin activity and aldosterone were increased in 2K1C rats compared with sham controls. HRP-treated 2K1C rats tended to lower plasma renin activity but showed similar aldosterone levels as vehicle-treated 2K1C rats. Our results indicate that blockade of the (P)RR with HRP does not improve target organ damage in renovascular hypertensive rats. , a single transmembrane-domain protein of 350 amino acids with a large unglycosylated and highly hydrophobic N-terminal domain and a short cytoplasmic tail of Ϸ20 amino acids that interacts with both renin and prorenin. The (P)RR is highly conserved across species. 2 The (P)RR binds renin and prorenin. When renin is bound to the (P)RR, the protein initiates extracellular signal regulated kinase 1/2 mitogen-activated protein kinase activation that is independent of angiotensin (Ang) II. 1,3,4 Furthermore, renin bound to the (P)RR displays a 3-to 5-fold increased catalytic activity compared with renin in solution. 1,5 Prorenin, which normally shows no catalytic activity in solution, is nonproteolytically activated when bound to the (P)RR. 1,5 Suzuki et al 6 investigated the mechanism of nonproteolytical activation of prorenin. They identified 2 regions in the prorenin segment, namely, T7PFKR10P and I11PFLKR15P. These regions are crucial for nonproteolytic activation. Ichihara et al 7 have synthesized a decoy peptide corresponding with the structure of this handle region (handle-region peptide [HRP]) and assumed that HRP must competitively bind to (P)RR as a decoy peptide, thereby inhibiting the nonproteolytic activation of prorenin.The group provided numerous remarkable studies demonstrating that HRP treatment in diabetic mice and rats improved nephropathy without affecting blood glucose levels. [7][8][9] The group also showed that HRP ameliorated renal and cardiac damage in hypertensive spontaneou...