UMOD

UMOD Full Name

uromodulin

UMOD Introduction

Uromodulin (UMOD), also known as Tamm-Horsfall protein, is the most abundant protein in human urine and has long been considered a biomarker of kidney function. The expression of the gene encoding UMOD is strictly confined to epithelial cells in the thick ascending limb (TAL) of the nephron and partially in the distal convoluted tubule (DCT). This highly regionalized expression pattern suggests that its function is closely related to the physiological activities of these specific tubular segments, such as salt reabsorption and urine concentration. The biosynthesis of UMOD is a multi-step, precisely regulated process. Within the endoplasmic reticulum (ER) of TAL cells, the UMOD gene is transcribed and translated into a precursor protein. This precursor is transiently attached to the cell membrane via a glycosylphosphatidylinositol (GPI) anchor at its C-terminus. After undergoing complex glycosylation modifications in the Golgi apparatus, the mature GPI-anchored UMOD protein is transported to the apical membrane (facing the tubular lumen). Here, a protease that has not yet been fully characterized cleaves the GPI anchor, releasing the UMOD protein into the forming urine. In the urine, UMOD monomers polymerize in a "head-to-tail" manner through interactions involving their ZP domains, forming enormous, linear, gel-like fibrous networks.

Figure 1. Expression, function and structure of uromodulin. (Source: Nanamatsu A, et al. 2024)

As a protein highly expressed in the TAL, UMOD plays a crucial role in maintaining renal physiological homeostasis. It functions by modulating the activity of key ion transport proteins on the apical membrane of TAL cells. Studies have shown that UMOD can upregulate the activity of the sodium‑potassium‑2 chloride cotransporter (NKCC2) and the renal outer medullary potassium channel (ROMK). NKCC2 pumps ions from the tubular fluid into the cell, while ROMK is responsible for "leaking" potassium back into the lumen, providing the necessary electrochemical gradient for NKCC2's continuous operation. By enhancing the function of these transporters, UMOD promotes salt reabsorption. Consequently, heritable differences in UMOD expression levels are associated with blood pressure levels and the risk of hypertension. Common genetic variants in the promoter region of the UMOD gene can lead to increased UMOD expression, thereby enhancing salt reabsorption and ultimately raising an individual's risk of developing hypertension. Conversely, a deficiency of UMOD may lead to salt wasting and a tendency toward low blood pressure. Kidney stones form primarily through the crystallization, aggregation, and growth of supersaturated minerals (most commonly calcium oxalate) in the urine. Through its highly glycosylated surface and the fibrous networks formed by polymerization, UMOD inhibits stone formation at multiple levels. First, it can directly bind to calcium oxalate crystal nuclei in the urine, preventing these particles from aggregating and growing via a steric hindrance effect. Second, the polymer network of UMOD can "encapsulate" these crystals, preventing them from contacting and adhering to the surface of tubular epithelial cells, thereby inhibiting the formation and retention of stone nidi.

The urinary tract is continuously exposed to the threat of microbial invasion from sources such as gut flora. As the major macromolecule in urine, UMOD constitutes the first line of chemical and physical defense against these threats. The surface of the UMOD molecule is covered with a large number of high‑mannose‑type glycan chains, making it an ideal "decoy receptor." When uropathogenic Escherichia coli (UPEC) enters the urinary system, its Type 1 fimbriae preferentially bind to the abundant UMOD in the urine rather than to epithelial cells. This binding results in the bacteria being "trapped" within the gel network of UMOD and efficiently cleared from the body through urination. Beyond serving as a physical barrier and pathogen scavenger, UMOD also possesses direct immunomodulatory functions, which exhibit significant context‑dependency—it can act as both an anti‑inflammatory and a pro‑inflammatory agent. In a healthy urinary tract, UMOD may help maintain immune quiescence by suppressing unnecessary immune responses. When kidney tissue is damaged (e.g., due to ischemia‑reperfusion injury) or during severe infection, the cellular barrier is disrupted, and UMOD may leak from its normal luminal position into the renal interstitium. In this misplaced context, immune cells in the interstitium (such as macrophages and dendritic cells) recognize UMOD as an endogenous danger signal, or DAMP.

Alternate Names for UMOD

UMOD; uromodulin; THP; FJHN; HNFJ; THGP; HNFJ1; MCKD2; ADMCKD2; uromucoid; Tamm-Horsfall urinary glycoprotein;

• 1. Nanamatsu A, et al. Advances in uromodulin biology and potential clinical applications. Nat Rev Nephrol. 2024 Dec;20(12):806-821.
  2. Kipp A, et al. What Does Uromodulin Do? Clin J Am Soc Nephrol. 2020 Dec 31;16(1):150-153.