LIPA (Lysosomal Acid Lipase)

The lysosomal gatekeeper for lipid droplet catabolism — LIPA is the sole acid hydrolase responsible for digesting cholesterol esters and triglycerides delivered to the lysosome, connecting both endocytic LDL processing and autophagosomal lipid droplet delivery (lipophagy) to usable free cholesterol and fatty acids. Complete loss causes Wolman disease (fatal infancy); partial loss causes Cholesterol Ester Storage Disease (CESD). In aging, declining LIPA activity and lysosomal pH dysregulation are proposed to impair hepatic lipid clearance and contribute to NAFLD-associated lipotoxicity.

Identity

UniProt: P38571 (LIPA_HUMAN)
NCBI Gene: 3988
HGNC symbol: LIPA
Gene locus: chromosome 10q23.31
Mouse ortholog: Lipa (high sequence conservation; single gene, no paralogs)
Length (precursor): 399 amino acids; ~45.4 kDa calculated MW (UniProt P38571)
Mature form: signal peptide (aa 1–27) cleaved co-translationally; propeptide (aa 28–76) removed during lysosomal maturation; mature lysosomal chain aa 77–399 (~36.6 kDa calculated); N-linked glycosylation at 6 sites (N36, N72, N101, N161, N273, N321) increases apparent MW on SDS-PAGE; glycosylation not essential for catalytic activity (UniProt P38571)

Key functional domains

Signal peptide (aa 1–27): directs co-translational ER insertion; cleaved before lysosomal trafficking (UniProt P38571, PMID 8112342)
Propeptide (aa 28–76): removed during lysosomal maturation; mature enzyme chain begins at aa 77 (UniProt P38571, PMID 8112342 and 15269241)
Lipase catalytic core: Ser-Asp-His catalytic triad; serine acts as nucleophile; mechanism parallels other lipase family members (gastric lipase, lingual lipase — noted in Anderson 1991 cDNA cloning)
Lid domain: covers active site; structural gating of substrate access (common to lipase family)
Glycosylation sites: N-linked glycans contribute to stability and lysosomal targeting via mannose-6-phosphate receptor pathway

LIPA is classified in the acid lipase family alongside gastric and lingual lipases; Anderson 1991 noted the sequence similarities ¹.

Function

LIPA is a lysosomal acid hydrolase active at pH ~4.5 (lysosomal lumen). It hydrolyzes both:

Cholesterol esters → free cholesterol + fatty acid
Triglycerides → glycerol + fatty acids (3 acyl chains)

Two substrate delivery routes converge on LIPA:

Route 1: Endocytosis (LDL pathway)

LDL particles are taken up via LDL receptor-mediated endocytosis → early endosome → late endosome/lysosome. LIPA hydrolyzes the cholesterol esters in LDL core particles, releasing free cholesterol that is then exported from the lysosome via NPC1/NPC2 to supply cellular membranes and suppress SREBP-mediated cholesterol synthesis.

Route 2: Lipophagy (autophagosomal delivery)

Cytoplasmic lipid droplets (LDs) can be selectively engulfed by autophagosomes and delivered to autolysosomes — a process termed lipophagy ². Within the autolysosome, LIPA hydrolyzes the LD core lipids (triglycerides, cholesterol esters), releasing free fatty acids (FFAs) that are exported for mitochondrial β-oxidation. Singh et al. 2009 established this axis in hepatocytes: starvation induces lipophagy, LIPA activity in autolysosomes drives FFA release, and blocking autophagy causes LD accumulation ².

Importantly: chaperone-mediated-autophagy (CMA) can degrade perilipins (PLINs) from the LD surface, which is a prerequisite for lipophagy access to the LD core lipids; LIPA then acts downstream once the LD reaches the autolysosome.

Dimension	Status
Pathway conserved in humans?	yes — LIPA is the sole LAL enzyme; lipophagy→LIPA axis demonstrated in rodent and human hepatocyte-derived cells
Phenotype conserved in humans?	yes — complete LIPA loss in humans causes Wolman disease; partial loss causes CESD with liver disease
Replicated in humans?	partial — disease phenotypes are human data; lipophagy flux specifically in aged human hepatocytes is not well-characterized

Discovery and cDNA cloning

Wolman disease — first described in 1961 (Wolman et al.); acid esterase/lipase deficiency recognized as the biochemical basis by Patrick and Lake (~1969) in a case series ³.
LIPA cDNA cloning — Anderson et al. 1991 reported cloning and expression of cDNA encoding human lysosomal acid lipase/cholesteryl ester hydrolase; noted sequence homology to gastric and lingual lipases ¹.

Diseases of LIPA deficiency

Both conditions are autosomal recessive (biallelic pathogenic variants in LIPA). The clinical spectrum is continuous, driven by residual enzyme activity.

Feature	Wolman Disease (complete loss)	CESD (partial loss)
Onset	Neonatal / infantile (weeks)	Childhood to adult
LAL residual activity	~0%	~1–10% (variable)
Hepatic findings	Rapidly fatal hepatic failure	Hepatomegaly, steatohepatitis, progressive fibrosis → cirrhosis
Adrenal calcification	Characteristic bilateral calcification	Absent
Other	Failure to thrive, diarrhea, hepatosplenomegaly	Dyslipidemia (elevated LDL-C, low HDL-C)
Prognosis without treatment	Fatal within first year	Progressive; premature atherosclerosis and liver failure

The infantile-onset form was historically called “Wolman disease” and childhood/adult-onset “CESD”; current nomenclature groups both as LAL deficiency (LAL-D) with a spectrum ⁴.

Therapeutic intervention: sebelipase alfa (Kanuma)

Sebelipase alfa is recombinant human lysosomal acid lipase (rhLAL) produced in transgenic eggs (Alexion Pharmaceuticals). It is delivered IV and taken up by mannose-6-phosphate receptor-mediated uptake into lysosomes.

FDA approval: December 2015 (both Wolman disease/infantile-onset and CESD/later-onset)
Mechanism: enzyme replacement therapy (ERT) — restores lysosomal LAL activity
Phase 3 evidence: Burton et al. 2015 (NEJM) — multicenter, placebo-controlled RCT in patients with LAL-D (later-onset); primary endpoint normalization of ALT levels; secondary endpoints included LDL-C, HDL-C, hepatic fat fraction ⁵
Limitations: lifelong IV infusion required; high cost; does not address CNS (not significant for LAL-D); ERT does not prevent progression to established cirrhosis

dose-response-unclear — optimal dosing and frequency in adults with CESD and various degrees of hepatic fibrosis not fully characterized in long-term follow-up.

Aging relevance

Lipophagy and hepatic lipid homeostasis

The Singh 2009 lipophagy paper ² establishes the autophagy → LIPA axis as critical for hepatic lipid catabolism during nutrient deprivation. This is directly relevant to aging because:

Autophagy flux declines with age — a feature of disabled-macroautophagy; reduced lipophagy delivery to lysosomes means less lipid reaches LIPA
Lysosomal pH dysregulation in aging — the acidic pH optimum of LIPA (~4.5) depends on maintained lysosomal acidification; aged cells show impaired v-ATPase function and lysosomal alkalinization, which could directly compromise LIPA activity even when enzyme protein is present needs-human-replication
NAFLD connection — lipophagy failure → LD accumulation → hepatic steatosis is one proposed mechanism for age-associated NAFLD/MASLD progression; LIPA sits at the bottleneck

needs-human-replication — Age-associated decline in hepatic LIPA expression or activity in humans is not well-characterized in primary literature as of this writing.

Atherosclerosis and common variants

Beyond rare complete/partial deficiency, common LIPA coding variants are associated with coronary artery disease (CAD) risk in population genetics:

rs1051338 — the best-characterized CAD-associated LIPA coding variant; Morris et al. 2017 showed this variant reduces LIPA enzyme levels and activity within lysosomes in functional assays ⁶.
Evans et al. 2019 further characterized multiple CAD-associated LIPA variants for their effects on enzyme levels and activity ⁷.

These findings are consistent with the mechanistic model: partial reduction in LIPA activity → impaired cholesterol ester hydrolysis in macrophage lysosomes → cholesterol accumulation → foam cell formation → accelerated atherosclerosis.

Dimension	Status
Pathway conserved in humans?	yes — same LDL → lysosome → LIPA → free cholesterol pathway
Phenotype conserved in humans?	yes — LIPA partial LOF → foam cells and atherosclerosis is directly human
Replicated in humans?	yes (association), partial (functional characterization in cell models)

The atherosclerosis angle links LIPA to the deregulated-nutrient-sensing hallmark via cholesterol metabolism dysfunction, though the connection is tangential — the primary hallmark connection is disabled-macroautophagy via lipophagy.

Lysosomal axis in aging

LIPA functions entirely within the lysosomal compartment, placing it at the intersection of multiple aging-relevant failures:

Declining lysosomal acidification reduces enzyme activity (pH-sensitivity)
Reduced autophagy flux reduces substrate delivery
Lipid droplet accumulation in aged hepatocytes, macrophages, and other cell types may reflect in part attenuated LIPA-mediated catabolism

See lipophagy for the upstream delivery mechanism and chaperone-mediated-autophagy for the PLIN-degradation prerequisite.

Pathway membership

lipophagy — primary downstream effector; LIPA hydrolyzes LD lipids delivered via autophagosome
autophagy — parent process
disabled-macroautophagy hallmark — lipophagy decline with age affects LIPA substrate delivery
deregulated-nutrient-sensing hallmark — tangential via cholesterol ester → free cholesterol recycling and LDL metabolism

Limitations and gaps

needs-human-replication — Age-dependent decline in hepatic LIPA protein expression or activity has not been quantified in aged human tissue with adequate power
needs-human-replication — Whether lysosomal pH rise in aged cells materially reduces LIPA activity in vivo has not been directly demonstrated
no-mechanism — Mechanism linking age-related autophagy decline to LIPA substrate deprivation vs. pH-dependent activity reduction is not resolved
long-term-unknown — Long-term efficacy and safety of sebelipase alfa ERT in the CESD adult population (progressive liver disease trajectory with treatment) is incompletely characterized
needs-canonical-id — GenAge entry for LIPA: none confirmed (LIPA is not listed in the GenAge human genes database as of seeding date; tagging for verification)

Footnotes

doi:10.1016/s0021-9258(18)54597-x · Anderson RA et al. · in-vitro (cDNA cloning + expression) · model: human LIPA cDNA; similarity to gastric/lingual lipases noted · Journal of Biological Chemistry 1991 · 145 citations (archive: confirmed, download pending) ↩ ↩²
singh-2009-lipophagy · doi:10.1038/nature07976 · Singh R et al. · in-vitro + in-vivo · n=not applicable (mechanistic) · model: primary mouse hepatocytes + Atg7-KO mice · Nature 2009 · 3,816 citations (archive: local PDF available at ; previously verified on lipophagy) ↩ ↩² ↩³
Patrick AD, Lake BD. ~1969. Original description of LAL deficiency (acid esterase/lipase) in the Journal of Medical Genetics. unsourced — the DOI 10.1136/jmg.6.4.448 supplied in the task brief resolves in the archive to an unrelated microbiology journal issue (title mismatch confirmed); the correct DOI for Patrick & Lake Wolman series could not be confirmed via PubMed eutils search. This citation is flagged for manual verification before use. ↩
NBK305870 · Balwani M, Vijay S. GeneReviews: Lysosomal Acid Lipase Deficiency. University of Washington. Last updated 2026. No DOI (book chapter); used for clinical spectrum description only. ↩
doi:10.1056/NEJMoa1501365 · Burton BK et al. · rct · n=66 (36 sebelipase alfa, 30 placebo) · Phase 3 multicenter double-blind placebo-controlled · primary endpoint: ALT normalization (31% [11/36] vs 7% [2/30], p=0.03); hepatic fat content significantly reduced (p<0.001) · model: LAL deficiency patients (later-onset) · New England Journal of Medicine 2015 · 238 citations (archive: confirmed; PDF pending — bronze OA; framing verified against PubMed abstract PMID 26352813; corrected from brief-supplied DOI 10.1056/NEJMoa1407972 which is not in archive) ↩
doi:10.1161/atvbaha.116.308734 · Morris GE et al. · in-vitro · model: cell-based functional assays; rs1051338 variant · Arteriosclerosis Thrombosis and Vascular Biology 2017 · 38 citations (archive: confirmed, download pending) ↩
doi:10.1161/atvbaha.119.313443 · Evans TD et al. · in-vitro · model: cell-based functional characterization of CAD-associated LIPA variants · Arteriosclerosis Thrombosis and Vascular Biology 2019 · 24 citations (archive: confirmed, download pending) ↩

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