Heat Shock Proteins in MASLD: Molecular Mechanisms, ER Stress, and Emerging Therapeutic Targets

Metabolic-associated steatotic liver disease (MASLD), previously known as non-alcoholic fatty liver disease (NAFLD), represents one of the most prevalent chronic liver disorders worldwide and is closely linked to obesity, insulin resistance, and type 2 diabetes. While early-stage steatosis is often reversible, persistent metabolic stress can drive progression to steatohepatitis, fibrosis, and cirrhosis. Increasing evidence indicates that heat shock proteins (HSPs), a conserved family of molecular chaperones, play critical regulatory roles in the molecular mechanisms underlying MASLD.

HSPs modulate key pathogenic processes, including lipid metabolism, endoplasmic reticulum (ER) stress, mitochondrial dysfunction, oxidative stress, inflammation, and apoptosis. Small HSPs influence autophagy and lipid clearance, while mitochondrial HSP60 supports fatty acid oxidation and metabolic homeostasis. Members of the HSP70 family, particularly GRP78 (BiP), serve as central regulators of the unfolded protein response (UPR), linking chronic ER stress to hepatocyte injury and inflammatory signaling. In contrast, HSP72 exhibits protective effects by enhancing mitochondrial integrity and suppressing pro-inflammatory pathways. Conversely, HSP90 promotes lipogenesis through stabilization of transcription factors such as SREBP and PPARγ, contributing to hepatic lipid accumulation.

Therapeutic strategies targeting HSP pathways—including natural compounds, pharmacological agents, and lifestyle interventions—have shown promise in preclinical models by restoring proteostasis, reducing ER stress, and improving metabolic resilience. Although clinical validation remains limited, modulating HSP activity represents a mechanistically coherent and potentially transformative approach to MASLD management. Understanding the subtype-specific functions of HSPs may facilitate the development of targeted interventions aimed at interrupting disease progression at the molecular level.

The Growing Burden of NAFLD/MASLD and Why Molecular Targets Matter

Non-alcoholic fatty liver disease (NAFLD), recently redefined as metabolic-associated steatotic liver disease (MASLD), has emerged as one of the most prevalent chronic liver disorders worldwide. Affecting approximately one in four adults globally, NAFLD is strongly associated with obesity, insulin resistance, type 2 diabetes, and dyslipidemia. The terminology shift from NAFLD to MASLD reflects a growing understanding that metabolic dysfunction—not simply the absence of alcohol consumption—is the primary driver of disease progression. This reframing underscores the systemic metabolic nature of fatty liver disease and aligns diagnostic criteria with its underlying pathophysiology.

MASLD encompasses a broad clinical spectrum ranging from simple hepatic steatosis (fat accumulation in hepatocytes) to metabolic-associated steatohepatitis (MASH), characterized by inflammation, hepatocyte injury, and fibrosis. In advanced stages, MASH may progress to cirrhosis, liver failure, or hepatocellular carcinoma. While early-stage steatosis is often asymptomatic and potentially reversible, progression to inflammatory and fibrotic stages significantly increases morbidity and mortality risk. Consequently, understanding the molecular mechanisms that govern disease transition has become a critical priority in hepatology research.

At the cellular level, MASLD pathogenesis is driven by a convergence of metabolic and stress-related insults. Excess caloric intake and insulin resistance promote increased free fatty acid influx and de novo lipogenesis in hepatocytes, overwhelming lipid handling capacity. This lipid overload induces lipotoxicity, mitochondrial dysfunction, oxidative stress, and chronic inflammation. Importantly, one of the central stress pathways activated during this process is endoplasmic reticulum (ER) stress. The accumulation of misfolded proteins in the ER triggers the unfolded protein response (UPR), which initially serves as an adaptive mechanism but becomes maladaptive under sustained metabolic stress.

Heat shock proteins (HSPs), a family of molecular chaperones, play pivotal roles in maintaining cellular proteostasis under these conditions. By regulating protein folding, degradation, inflammatory signaling, and mitochondrial integrity, HSPs sit at the intersection of lipid metabolism, oxidative stress, and ER stress pathways. Emerging evidence suggests that specific HSP subtypes may either exacerbate or mitigate fatty liver progression, positioning them as both mechanistic biomarkers and potential therapeutic targets. As MASLD continues to rise in parallel with global metabolic disorders, identifying and modulating such molecular regulators may represent a key strategy in preventing disease escalation.

Heat Shock Proteins: Central Stress Regulators in Fatty Liver Disease

Heat shock proteins (HSPs) are a highly conserved family of molecular chaperones that safeguard cellular proteostasis under physiological and pathological stress. In the context of metabolic-associated steatotic liver disease (MASLD), HSPs have emerged as key modulators of lipid metabolism, mitochondrial integrity, inflammation, and endoplasmic reticulum (ER) stress. Their functions extend beyond simple protein folding; they orchestrate complex signaling networks that determine whether hepatocytes adapt to metabolic overload or progress toward injury and fibrosis.

HSPs are commonly classified according to molecular weight and subcellular localization, including small HSPs (e.g., HSP20, HSP27), mitochondrial chaperonins (HSP60), cytosolic stress proteins (HSP70 family), ER-resident chaperones (GRP78/BiP), and the ATP-dependent HSP90 family. Each subgroup contributes uniquely to liver pathophysiology.

Small HSPs exhibit context-dependent effects in MASLD. HSP20 has been shown to suppress autophagy, thereby exacerbating lipid accumulation and hepatocyte lipotoxicity under high-fat conditions. In contrast, phosphorylated HSP27 enhances autophagic flux and promotes lipid clearance, highlighting how post-translational modifications can determine protective versus pathogenic outcomes. These opposing roles underscore the importance of autophagy regulation in steatotic liver progression.

HSP60, primarily localized in mitochondria, supports fatty acid oxidation and preserves mitochondrial homeostasis. By stabilizing mitochondrial proteins and facilitating oxidative metabolism, HSP60 helps mitigate reactive oxygen species (ROS) generation and improves insulin sensitivity. Reduced HSP60 expression has been associated with impaired mitochondrial function and enhanced inflammatory signaling in metabolic liver disease.

Members of the HSP70 family play particularly complex roles. Cytosolic HSP70 can suppress inflammatory pathways such as NF-κB and JNK, conferring cytoprotection. However, excessive HSP70 activity has also been linked to increased lipogenic gene expression in hepatocytes. GRP78 (glucose-regulated protein 78), an ER-resident HSP70 homolog, is central to the unfolded protein response (UPR). While transient GRP78 activation restores ER homeostasis, sustained upregulation reflects chronic ER stress and correlates with steatohepatitis severity.

HSP90, another ATP-dependent chaperone, stabilizes key metabolic regulators including Akt, SREBP, and PPARγ. By enhancing the activity of lipogenic transcription factors, HSP90 may promote hepatic lipid accumulation. Consequently, selective inhibition of HSP90 is being explored as a strategy to correct dysregulated lipid synthesis.

Collectively, heat shock proteins function as molecular decision-makers in MASLD, balancing adaptation and injury. Understanding their subtype-specific roles provides a framework for targeted therapeutic modulation in metabolic liver disease.

GRP78 and Endoplasmic Reticulum Stress: A Central Axis in MASLD Progression

Among the heat shock protein families implicated in metabolic-associated steatotic liver disease (MASLD), glucose-regulated protein 78 (GRP78), also known as BiP, occupies a particularly central role. GRP78 is an endoplasmic reticulum (ER)-resident chaperone and a master regulator of the unfolded protein response (UPR), a signaling network activated when misfolded or unfolded proteins accumulate in the ER lumen. In metabolically stressed hepatocytes, chronic lipid overload and insulin resistance place sustained pressure on protein folding capacity, leading to persistent ER stress and prolonged UPR activation.

Under physiological conditions, GRP78 binds to three key ER transmembrane sensors—PERK (protein kinase RNA-like ER kinase), IRE1α (inositol-requiring enzyme 1α), and ATF6 (activating transcription factor 6)—maintaining them in an inactive state. When misfolded proteins accumulate, GRP78 dissociates to assist in protein refolding, thereby allowing these sensors to initiate downstream signaling. Initially, this response is adaptive: PERK-mediated phosphorylation of eIF2α reduces protein synthesis, IRE1α promotes XBP1 splicing to enhance chaperone production, and ATF6 upregulates genes that restore ER homeostasis. However, under chronic metabolic stress, these pathways shift from protective to pathogenic.

In MASLD, sustained GRP78 upregulation is frequently observed in association with hepatic steatosis and steatohepatitis. Persistent activation of PERK–eIF2α–CHOP signaling promotes apoptosis, while prolonged IRE1α activation enhances inflammatory signaling via JNK and NF-κB pathways. These molecular events contribute to hepatocyte injury, macrophage recruitment, and fibrogenesis. Moreover, ER stress intersects with lipid metabolism: activation of UPR components can increase de novo lipogenesis through transcriptional regulators such as SREBP-1c, further amplifying hepatic fat accumulation.

GRP78 also interfaces with inflammasome activation. Evidence suggests that GRP78-mediated ER stress enhances NLRP3 inflammasome signaling, promoting the release of pro-inflammatory cytokines such as IL-1β. In parallel, oxidative stress and mitochondrial dysfunction exacerbate ER stress, creating a vicious cycle of metabolic injury. Importantly, while transient GRP78 induction may serve a compensatory role, chronic overactivation reflects unresolved cellular stress and correlates with disease severity.

Fig. 1 GRP78-Mediated ER Stress Signaling as a Central Driver of MASLD Progression

Given its dual function as both a stress sensor and regulatory hub, GRP78 represents a compelling therapeutic target. Modulating ER stress responses to restore adaptive UPR signaling—without triggering apoptotic pathways—may offer a promising strategy to interrupt MASLD progression at a fundamental molecular level.

HSP90 and HSP72: Lipid Metabolism Control and Therapeutic Implications in MASLD

Beyond ER stress regulators, two additional heat shock protein families—HSP90 and HSP72—play critical yet contrasting roles in metabolic-associated steatotic liver disease (MASLD). While HSP72 generally exerts protective metabolic effects, HSP90 is increasingly recognized as a facilitator of lipid dysregulation and disease progression.

HSP90 is an ATP-dependent molecular chaperone responsible for stabilizing and activating a wide array of client proteins, including kinases and transcription factors central to metabolic signaling. In hepatocytes exposed to metabolic stress, HSP90β has been shown to promote lipogenesis through the Akt–GSK3β–FBW7–SREBP axis. Mechanistically, HSP90 enhances Akt phosphorylation, which inhibits GSK3β activity. This inhibition prevents the proteasomal degradation of mature sterol regulatory element-binding proteins (mSREBPs), key transcription factors that drive de novo fatty acid and cholesterol synthesis. The resulting accumulation of mSREBPs amplifies lipogenic gene expression, contributing directly to hepatic steatosis.

In addition, HSP90 stabilizes peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor that promotes lipid uptake and storage. Elevated HSP90 activity therefore reinforces transcriptional programs favoring triglyceride accumulation. Experimental inhibition of HSP90 disrupts these interactions, reduces lipogenic signaling, and attenuates hepatic fat deposition in preclinical models. These findings position HSP90 as a potential therapeutic target for interrupting maladaptive lipid synthesis pathways in MASLD.

In contrast, HSP72—a stress-inducible member of the HSP70 family—demonstrates largely protective effects in metabolic liver disease. HSP72 enhances mitochondrial integrity and promotes fatty acid oxidation, thereby reducing intracellular lipid accumulation. It also suppresses pro-inflammatory signaling by inhibiting c-Jun N-terminal kinase (JNK) activation, a pathway strongly implicated in insulin resistance and hepatocyte apoptosis. Increased hepatic HSP72 expression has been associated with improved glucose tolerance, enhanced insulin sensitivity, and reduced oxidative stress in diet-induced models of fatty liver.

Importantly, HSP72 induction appears to counterbalance some of the deleterious effects of chronic metabolic stress. By stabilizing mitochondrial function and dampening inflammatory cascades, HSP72 helps preserve hepatocyte viability under lipotoxic conditions. These opposing roles of HSP90 and HSP72 illustrate how distinct molecular chaperones can either exacerbate or mitigate MASLD progression depending on their regulatory networks and downstream targets.

Collectively, targeting HSP90 inhibition while promoting HSP72 induction may represent a rational dual strategy for restoring metabolic homeostasis and limiting steatotic liver progression.

Therapeutic Strategies Targeting Heat Shock Proteins in MASLD

Given the central role of heat shock proteins (HSPs) in regulating lipid metabolism, endoplasmic reticulum (ER) stress, mitochondrial function, and inflammation, therapeutic modulation of HSP pathways has emerged as a promising strategy in metabolic-associated steatotic liver disease (MASLD). Rather than acting on a single metabolic enzyme, HSP-targeted approaches aim to restore cellular proteostasis and rebalance stress signaling networks disrupted by chronic lipid overload.