Role of GSTM1 in Hypertension, CKD, and Related Diseases across the Life Span

Abstract

Over 20 years after the introduction of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, CKD remains a major public health burden with limited therapeutic options to halt or slow kidney disease progression at all ages. The consensus is that oxidative stress contributes to CKD development and progression. Yet, to date, there is no clear evidence that broad use of antioxidant therapy provides a beneficial effect in CKD. Understanding the specific pathophysiologic mechanisms in those who are genetically most susceptible to oxidative stress is a crucial step to inform therapy in an individualized medicine approach, considering differing exposures and risks across the life span. Glutathione-S-transferase μ 1 (GSTM1) is a phase 2 enzyme involved in inactivation of reactive oxygen species and metabolism of xenobiotics. In particular, those with the highly prevalent GSTM1 null genotype (GSTM1[0/0]) may be more susceptible to kidney disease progression, due to impaired capacity to handle the increased oxidative stress burden in disease states, and might specifically benefit from therapy that targets the redox imbalance mediated by loss of the GSTM1 enzyme. In this review, we will discuss the studies implicating the role of GSTM1 deficiency in kidney and related diseases from experimental rodent models to humans, from the prenatal period through senescence, and the potential underlying mechanism.

Introduction

CKD is a significant cause of morbidity and mortality across the life span. The etiology of CKD changes with age, with structural and inflammatory causes predominating in childhood (¹), and hypertension (HTN) and diabetes mellitus gaining importance in adulthood (²). Pathways for progression of disease, regardless of etiology, include nephron hypertrophy (³) and impaired glomerular filtration (⁴) leading to nephron loss; these result in a final common pathway of interstitial inflammation and fibrosis (⁴,⁵).

GSTM1 belongs to the superfamily of glutathione-S-transferases (GSTs) of phase 2 enzymes that catalyze a number of distinct glutathione-dependent reactions (^6–8). The primary role of GSTs is the metabolism of xenobiotics, a broad range of reactive oxygen species (ROS), and electrophilic compounds, such as reactive aldehydes. These enzymes use glutathione to inactivate ROS, generating oxidized glutathione. It follows that a deficiency in GSTs would decrease the capacity to handle oxidative stress. Of the 13 identified classes of soluble GSTs (^6–8), GSTM1 is one of the five μ-class GST enzymes in humans (⁹) and is evolutionarily quite conserved. In the mouse kidney, GSTM1 is the most abundantly expressed isoform among all GST enzymes (¹⁰). The Gstm gene family is among several Gsts regulated by the Nrf2 transcription factor (¹¹).

Whereas most large gene deletion polymorphisms are primarily noncoding sequences (¹²), the GSTM1 gene has a complete gene deletion variant that reaches major allele status in many human populations, reaching 70% in most human populations. Approximately 27% of Black individuals and 50% of White and Asian individuals are homozygous carriers of the GSTM1 deletion or null allele (GSTM1[0]) (¹³). Those with the deletion variant lack GSTM1 enzyme function (^14–19). Chimpanzees are the only other primate species that have the common GSTM1 deletion, reaching 0.41 (41%) in allele frequency among these primates (²⁰). The GSTM1 deletion event is thought to have occurred independently in both human and chimpanzee species nearly 400,000 years ago, likely under non-neutral (or nonrandom) forces and with unclear evolutionary effect (²⁰). A less common GSTM1 gene variant is the insertion variant that can result in carriers with three copies of the GSTM1 gene (²¹). Why the deletion variant is so common among human populations remains unknown because there is a growing body of evidence suggesting GSTM1 plays an important role in determining disease susceptibility from the prenatal period to aging. This susceptibility includes altered risks for the conditions that predispose to kidney disease, increased risk of incidence of CKD, increased risk of rapid progression of CKD, and altered risks of complications of CKD, discussed below.

Role of GSTM1 in Modulating Oxidative Stress: Evidence from Experimental Studies

Although numerous studies demonstrated that GSTM1 deficiency is associated with many disease states, the mechanism by which it modifies disease development or course remains poorly understood. There is accumulating evidence that modulation of oxidative stress is a key mechanism by which GSTM1 influences disease susceptibility. In this regard, Gstm1 was identified as a positional candidate gene in a quantitative trait locus for HTN in the rat (²²,²³).

Gstm1 mRNA and protein levels in the kidney were found to be reduced in the stroke-prone spontaneously hypertensive rat, compared with the normotensive congenic and Wistar Kyoto rats (²⁴), and were inversely correlated with kidney tissue levels of ROS. This suggests the protective role of GSTM1 in HTN likely involves defense against oxidative stress (²⁴).

Gstm1 was also identified as a candidate gene for susceptibility to renal vascular remodeling in the mouse (²⁵). Cause and effect was established in vitro: small-interfering RNA knockdown of Gstm1 resulted in increased ROS levels and vascular smooth muscle cell proliferation (which is a typical response to oxidative stress) in a dose-dependent manner (²⁶). Chang et al. (²⁷) reported that the ischemic reduction of renal mass (RRM) model of CKD in the mouse resulted in increased expression of Nrf2 and GSTM1, and increased levels of the reactive aldehyde 4-hydroxy-2-nonenal, a product of lipid peroxidation. Because GSTM1 directly regulates 4-hydroxy-2-nonenal protein adducts in vascular smooth muscle cells, the findings suggest that, in conditions of increased oxidative stress, such as CKD, Gstm1 is upregulated by Nrf2 as an adaptive response to combat oxidative stress (²⁷).

To establish causality in vivo, Gigliotti et al. (²⁸) generated a global Gstm1 gene knockout (KO) mouse line. At baseline, Gstm1-KO mice displayed higher levels of urinary markers of oxidative stress but no discernible kidney pathology. However, when subjected to the angiotensin II model of HTN and the RRM model of CKD, Gstm1-KO mice had increased renal superoxide levels and kidney pathology, characterized by exaggerated glomerulosclerosis; tubulointerstitial inflammation with increased number of neutrophils, F4/80+ cells, T cells, and B cells; and increased expression of MCP-1, CXCL-1, and IL-6, independent of BP (²⁸). In the RRM model, >60% of Gstm1-KO mice died by 8 weeks after RRM and displayed accelerated glomerulosclerosis and renal inflammation, whereas 100% of wild-type mice survived to 13 weeks when the study period ended. Because Gstm1 is ubiquitously expressed, in the kidney along the entire renal tubule, particularly in the proximal tubule (https://esbl.nhlbi.nih.gov/helixweb/Database/NephronRNAseq/All_transcripts.html), and in the vasculature and bone marrow, to delineate the relative contribution of bone marrow versus parenchymal GSTM1 in inflammation, a bone marrow crosstransplantation experiment found that Gstm1 deletion in the parenchyma, and not in the bone marrow, determined renal inflammation (²⁸). Of note, staining for macrophages showed that the major macrophage population was the interstitial resident macrophages (CD11b^lowF4/80^high), and there were much fewer blood-derived infiltrating macrophages (CD11b^highF4/80^low) (²⁸). It remains to be delineated which GSTM1-deficient cell type(s) in the kidney drives oxidative stress, inflammation, and kidney injury.

Tissue-specific deletion of Gstm1 in experimental models can determine the precise contribution of Gstm1 in renal tubules and resident macrophages in HTN and CKD.

Administration of TEMPOL, an SOD mimetic, attenuated the kidney injury and inflammation observed in Gstm1-KO mice, illustrating that oxidative stress was a key driver of kidney disease in Gstm1-KO mice. Despite the significant increase in kidney superoxide levels at baseline and in disease states (²⁸), Gstm1-KO mice displayed no difference in expression of the NADPH subunits Nox2 and Nox 4 (²⁸) that are the major producers of superoxide in the kidney.

As a member of the GST superfamily, there is no evidence that GSTM1 enzyme directly modulates superoxide levels. The molecular pathway by which GSTM1 influences superoxide levels (production versus accumulation) remains to be determined.

In an in vitro model of AKI using HK-2 cells subjected to hypoxia/reoxygenation, GSTM1 was shown to be downregulated directly by miR-425-5p through the use of an miR-425-5p mimetic and inhibitor, and this downregulation was associated with increased endoplasmic reticulum stress and oxidative stress (²⁹). Similarly, in rats subjected to the ischemia-reperfusion injury model of AKI, miR-423-5p was shown to be upregulated in the kidney, and this was associated with decreased Gstm1 mRNA and protein levels and decreased kidney function. Treatment with an miR-423-5p mimetic further decreased GSTM1 protein expression and worsened kidney function, whereas treatment with an miR-423-5p inhibitor increased GSTM1 protein expression and improved kidney function (²⁹). Whether the effect of miR-423-5p is specifically dependent on GSTM1 or is also mediated by a non-GSTM1 pathway(s) is unclear, and whether the miR-423-5p–GSTM1 axis also plays a role in CKD remains to be delineated.

Nevertheless, the evidence suggests that GSTM1 plays a direct role in oxidative stress in both experimental models of AKI and CKD. In addition to its enzymatic/catalytic activity, GSTM1 binds to the apoptosis signaling-regulating kinase-1 (ASK1), thereby inhibiting ASK1 activation (³⁰). In vitro binding assays indicated that the carboxy-terminal domain of the mouse GSTM1 binds to the amino-terminal region of ASK1 (³⁰). Under conditions of stress, GSTM1 dissociates from ASK1, resulting in ASK1 activation that then activates the c-Jun amino-terminal kinase and mitogen-activated protein kinase p38 pathways, which promote apoptosis and production of inflammatory cytokines (³⁰,³¹). This effect is independent of the enzymatic activity of GSTM1 (³⁰). However, the relative contribution of GSTM1’s enzymatic function and the ASK-dependent effect of GSTM1 in health and disease states, particularly in HTN and CKD, remains unknown.

Because GSTs are heterogeneous enzymes with significant, overlapping substrate specificities, findings illustrate that other GST phase 2 enzymes do not compensate adequately for the loss of GSTM1, and thus their induction by pharmacologic/dietary factors may be required to lower oxidative stress. In this regard, sulforaphane, a bioactive product found in cruciferous vegetables, which results from the conversion of glucoraphanin by the enzyme myrosinase, has been shown to be potent in inducing phase 2 detoxification enzymes by blocking Keap-1–mediated ubiquitination of Nrf2 that is marked for degradation. This results in increased availability of Nrf2, which translocates to the nucleus and transcriptionally activates genes with an antioxidant response element in their promoters, including GST genes (³²).

The Nrf2-GSTM1 pathway and the effect of sulforaphane in modulating oxidative stress is summarized in Figure 1. See Liebman and Le (³³) for a detailed discussion of the sulforaphane-Nrf2 pathway in kidney disease. Gigliotti et al. (²⁸) reported that sulforaphane-rich broccoli powder induced Gstm1 in wild-type mice, but not in Gstm1-KO mice. However, Gstm1-KO mice, and not wild-type mice, derived a renal protective effect when their diet was supplemented with a powder form of sulforaphane-rich cruciferous vegetable broccoli (²⁸). Importantly, although homozygous carriers of the GSTM1(0) allele are more at risk for CKD progression (²⁷) and kidney failure (³⁴), these carriers also derived more benefit, with respect to kidney failure, from a high intake of cruciferous vegetables compared with those carrying one or two active GSTM1 alleles, similar to the findings in the mouse (²⁸). It is likely that the GSTM1 enzyme influences the bioavailability of sulforaphane. In this regard, free sulforaphane and its metabolites have been reported to be increased in GSTM1 null carriers compared with those with the active allele (³⁵).

Figure 1.: Nrf2-GSTM1 pathway protects against oxidative stress and is a potential novel therapeutic target. Under basal conditions, nuclear factor erythroid 2–related factor 2 (Nrf2) is ubiquitinated by Kelch-like ECH-associated protein 1 (KEAP-1) and is targeted for degradation. Under conditions of oxidative stress or treatment with sulforaphane, KEAP-1 can no longer bind to Nrf2; this, in turn, allows Nrf2 to migrate from the cell cytoplasm into the nucleus where it binds to the antioxidant responsive element (ARE) in the promoter regions of Nrf2 target genes, including glutathione-S-transferase μ 1 (GSTM1) and other antioxidant genes, thereby increasing their transcription and their activities. GSTM1 acts to decrease reactive oxygen species, but can also inhibit apoptosis signaling-regulating kinase-1 (ASK1), thereby preventing tissue injury, cell death, and inflammation. GSTM1 is downregulated by miRNA-425-5p. Potential novel therapies in the treatment of kidney disease includes the inhibition of miRNA-425-5p or treatment with sulforaphane, which can increase the activity of GSTM1 or other antioxidant genes, particularly in those who are homozygous for the GSTM1 null allele and, therefore, lack the enzyme.

The observation that only humans and mice with GSTM1 deficiency derive kidney protective benefits from an intake of cruciferous vegetables supports the notion that the gene-environment interaction plays an important role in disease outcomes and that therapy should be directed at those genetically susceptible in an individualized manner. A pilot study is underway to test the safety of sulforaphane in CKD (ClinicalTrials.gov identifier NCT05153174) as a first step in determining its potential as a therapeutic strategy in delaying kidney disease progression in a precision-medicine approach; this study may have far-reaching implications to those at risk, as discussed below.

Risks Associated with GSTM1 Deletions in the Prenatal Period

Maternal Risks

Most studies focusing on the role of GSTM1 in the prenatal period have been directed at determining an association between GSTM1 genotype and risk of preeclampsia, a systemic syndrome of pregnancy characterized by new or accelerating HTN and proteinuria.

Women with preeclampsia are at increased long-term risk of HTN, cardiovascular disease (³⁶), and kidney disease; offspring of a pregnancy complicated by preeclampsia are at higher risk of growth restriction, prematurity, higher body mass index, and elevated BP. The GSTM1 null allele has been associated with an increased risk of preeclampsia in several populations, including Serbian (³⁷), Bangladeshi (³⁸), and Mexican mestizo (³⁹) populations. However, other studies have not seen such an association, including in a Turkish population (⁴⁰). In fact, Guan et al. (⁴¹) reported a protective effect of the GSTM1 null polymorphism on development of preeclampsia. The authors hypothesize their unexpected results may be due to “ethnic differences in expression levels of other GSTs [leading] to differential susceptibility to environmental risk factors.” The irreproducibility of the results might also be attributed to a lack of comprehensive analysis of gene copy number variants (⁴²). There has been no studies on the role GSTM1 in preeclampsia in animal models. Although Gstm1 is a downstream target of Nrf2, deletion of Gstm1, in turn, upregulates Nrf2 protein expression, likely due to increased oxidative stress (²⁷). Therefore, it is tempting to speculate that the increased risk of preeclampsia associated with the GSTM1 null allele can be explained by the activation of Nrf2, which has been shown to decrease placental angiogenesis, suppress fetal growth, and worsen maternal survival (⁴³). Further research is needed to clarify the conflicting results in human preeclampsia and to delineate its potential mechanistic role using animal models.

Gestational diabetes is another common complication of pregnancy associated with adverse global and kidney outcomes. Maternal risks of gestational diabetes include nongestational diabetes (⁴⁴) and future cardiovascular disease (⁴⁵). For the children of mothers with gestational diabetes, complications that are directly related to kidney disease include increased rates of congenital anomalies of the kidneys and urinary tract (⁴⁶), metabolic syndrome (⁴⁷), and early-onset cardiovascular disease (⁴⁸). The GSTM1 null allele has been reported to associate with higher odds of gestational diabetes in several studies (^49–51), but a study by Orhan et al. (⁵²) reported no such association in a Turkish population. More studies are needed to determine the influence of gene-gene and gene-environment interactions on the effect of the GSTM1 genotype in different human populations.

Infant Risks

Several studies of environmental exposure suggest GSTM1 participates in the detoxification of compounds known to be associated with adverse kidney outcomes, including tobacco smoke (⁵³,⁵⁴), lead, and polycyclic aromatic hydrocarbons (⁵⁵). The studies show a modifying effect of the GSTM1 genotype in infants, with those possessing fewer functioning GSTM1 alleles being more susceptible to these adverse outcomes in childhood.

A number of investigations further demonstrate adverse outcomes known to be associated with kidney disease. Intrauterine growth restriction and prematurity are associated with lower nephron mass and increased lifetime CKD (⁵⁶). Danileviciute et al. (⁵⁷) reported the association between maternal smoking and low birth weight is mediated by GSTM1 genotype, with null genotypes resulting in lower birthweight, even with light smoking. Likewise, Kwon et al. (⁵⁸) showed a modification of the effect of perfluorinated compounds on birth weight by maternal GSTM1 genotype, as did Shin et al. (⁵⁹) with paraben exposure. Fetal genotype also appears to affect birth outcomes, with GSTM1 insertions associated with protection against prematurity (⁴²). Because nephron number may have an effect on the development of HTN and kidney disease later in life (⁶⁰,⁶¹), it remains to be determined whether the GSTM1 null genotype associates with nephron mass and numbers at birth.

Risks Associated with GSTM1 Deletion in Childhood

As in all stages of life, GSTM1 plays a role in detoxification of exogenous compounds and disease susceptibility in childhood. Children with medulloblastoma were 4.3 (95% CI, 1.1 to 16.8) times more likely to experience severe treatment toxicity with GSTM1 or GSTT1 null genotypes (⁶²). In the case of the nephrotoxin ifosfamide (an alkylating agent used commonly for the treatment of pediatric malignancy), however, it appears that GSTP1 polymorphisms, rather than GSTM1 deletion, associate with kidney injury (⁶³,⁶⁴).

GSTM1 deletion is associated with a number of childhood diseases that confer risk for CKD. For example, children with acute lymphoblastic leukemia (ALL) are at risk for kidney injury from leukemic infiltration, nephrotoxic chemotherapy, tumor lysis syndrome, thrombotic microangiopathies, and prerenal azotemia; 10%–30% of pediatric patients who survive ALL have persistent kidney insufficiency (⁶⁵). A recent meta-analysis of 30 individual studies found an odds ratio (OR) of 1.3 (95% CI, 1.105 to 1.523, P=0.001) for incidence of ALL in children with GSTM1 polymorphisms (⁶⁶). Interestingly, a recent study by Jurkovic Mlakar et al. (⁶⁷) reported that the GSTM1/GSTT1 double null genotype was an independent risk factor for post–hematopoietic stem cell transplantation relapse in children with ALL, acute myeloid leukemia, and myelodysplastic syndrome (adjusted hazard ratio, 6.52; 95% CI, 2.76 to 15.42; P<2.0×10^–5). Using immortalized nonmalignant lymphoblastoid cell lines (LCLs) genotyped for GSTM1 and GSTT1 null and non-null alleles, a human acute monocytic leukemia cell line model (THP1), and CRISPR/Cas9 gene editing to KO GSTM1 and GSTT1 in the THP1 cell line, the authors further showed that GSTM1, not GSTT1, determined the half-maximal inhibitory concentration for busulfan (BU), now commonly used in conditioning regimens before hematopoietic stem cell transplantation in these cell lines (⁶⁷). Importantly, Jurkovic Mlakar et al. showed that LCLs carrying the GSTM1 null genotype and THP1^GSTM1−/− cells had significantly higher cell viability (or less cell death) after treatment with BU compared with GSTM1 non-null LCLs and THP1^GSTM1+/+ cells, respectively. The GSTM1 null genotype was also associated with increased apoptosis after treatment with BU (⁶⁷), raising the question of whether the apoptosis is mediated via ASK1, as discussed above. The study showed that GSTT1 genotype primarily influenced baseline cell proliferation, with the LCLs carrying the GSTT1 null genotype and THP1^GSTT1−/− cells proliferating less than those expressing GSTT1.

In an Egyptian population, pediatric patients with GSTM1 null genotype and sickle cell disease were at significantly higher risk of vaso-occlusive crisis (⁶⁸). Sickle cell nephropathy leading to CKD is already present in 8%–12% of children (⁶⁹) and rises to 21% of adults (⁷⁰). Interestingly, analysis of data from the Combined Swedish Childhood Diabetes Registry and Diabetes Incidence Study showed that the presence of the functional GSTM1 allele was associated with susceptibility to type 1 diabetes in adolescents; the authors hypothesized that glutathione conjugation may be implicated in development of diabetes in this population (⁷¹).

Case-control studies have shown higher frequencies of GSTM1 deletion in children with advanced CKD, and that these children have biochemical evidence of impaired lipid and protein oxidation (⁷²). Recently, our group reported an association between GSTM1 deletion and risk of progression of pediatric CKD in the Chronic Kidney Disease in Children Study, which consists of a large, multicenter cohort (⁷³). Investigations to replicate this finding are ongoing, as are efforts to determine whether this effect is general to all CKD or specific to certain etiologies.

Risks Associated with GSTM1 Deletions in Adulthood

In adults, GSTM1 polymorphisms have also been clearly implicated in the development of chronic diseases associated with kidney insufficiency, including atherosclerotic coronary artery disease (⁷⁴,⁷⁵) and malignancy (⁷⁶,⁷⁷). With respect to genitourinary cancers specifically, there appears to be an association with bladder cancer (⁷⁸) and prostate cancer (⁷⁹). Meta-analyses looking at the role of the GSTM1 null allele in susceptibility to renal cell carcinoma have been mixed (⁸⁰,⁸¹); this may be related to the influence of gene-environment interaction for disease susceptibility.

Diabetes and HTN are the leading causes of kidney failure in adults in high- and middle-income countries (²). Investigation has been conducted on the role of GSTM1 polymorphisms in HTN, with mixed results in several recent meta-analyses (^82–84). Significant heterogeneity between individual studies in these analyses limits their overall interpretability. With respect to type 2 diabetes mellitus, multiple meta-analyses show an increased susceptibility to diabetes in those with GSTM1 deletion (⁵¹,⁸⁵,⁸⁶).

Several studies examined the effects of GSTM1 deletions on CKD and ESKD of individual homogenous populations. In an analysis of the African American Study of Kidney Disease (AASK) cohort of participants with CKD stages 3 and 4 whose kidney disease was attributable to hypertensive nephrosclerosis, Chang et al. (²⁷) reported there were no differences in baseline eGFR or serum creatinine among the GSTM1 genotypes at enrollment (prevalent CKD). Consistent with this finding, in a cross-sectional study, Hung et al. (⁸⁷) recently reported no risk of increased prevalent CKD with GSTM1 null genotype in a cohort of Black people with HIV in the United Kingdom, the majority of whom had normal kidney function. However, in prevalent ESKD, a case-control study of Northern Indian individuals showed increased odds of ESKD with GSTM1(0) (OR, 1.45; 95% CI, 1.03 to 2.02) (⁸⁸). In a Mexican case-control study, GSTM1 deletion was associated with ESKD of unknown etiology (OR, 2.05; 95% CI, 1.21 to 3.45) (⁸⁹). Similarly, a sex- and age-matched case-control study in Iran reported increased odds of ESKD in those with GSTM1 null genotype (OR, 3.04; 95% CI, 1.5 to 6.1) (⁹⁰).

With regards to CKD development or progression in adults, there have been four studies reporting the deleterious effects of the GSTM1 null allele. In AASK, Chang et al. (²⁷) reported that participants with one or two deletions in GSTM1 were more likely to reach the combined end point of reduction in GFR, dialysis, or death over the 5-year observation period, despite having similar baseline eGFR, as mentioned above. This was further characterized by Bodonyi-Kovacs et al. (⁹¹), who found, in the same AASK cohort, that the GSTM1 null allele had independent and similar effects as the APOL1 high-risk variants, and the two variants together conferred greater risk for CKD progression than either alone. Of interest, those with APOL1 high-risk alleles but who are homozygous for the GSTM1 active allele (GSTM1[1/1]) might be protected from CKD progression (⁹¹). In a 70-month prospective study of a Southern Indian population, heathy controls with a GSTM1 null allele had significantly increased odds of development of CKD (OR, 2.93; 95% CI, 1.89 to 4.53), and carriers of the GSTM1 null allele with preexisting CKD were more likely to progress to ESKD (OR, 1.84; 95% CI, 1.19 to 2.83) (⁹²). The same study also reported that, in patients with ESKD, those with the GSTM1 null allele had a 3.85-fold increased risk for death (⁹²). Similarly, in a study of Serbian patients with ESKD on hemodialysis, GSTM1(0) allele was significantly associated with both shorter overall (hazard ratio, 1.6; 95% CI, 1.1 to 2.3; P=0.02) and cardiovascular survival (hazard ratio, 2.1; 95% CI, 1.2 to 3.6; P=0.01) (⁹³). In the Atherosclerosis Risk in Communities cohort followed for 30 years, there was a significant association between time to ESKD and number of copies of functional GSTM1 (³⁴). In contrast, another large US community cohort reported no association between GSTM1(0) and risk of kidney failure (⁹⁴). However, the study’s low event rates (1% for the whole cohort) and relatively short follow-up time (mean, 9 years) (⁹⁴) suggest it may have been underpowered to detect differences in risk. Several key studies are summarized in Table 1. Taken together, the evidence in both adults and children suggest that GSTM1 deficiency augments or accelerates disease progression in those with preexisting kidney disease, consistent with the notion that GSTM1 is a modifier of kidney disease course, likely through its role in modulating oxidative stress.

Table 1. - Summary of key studies

Cohorts	Outcome	Study Type	Number of Patients	Number of Controls	Odds Ratio or Hazard Ratio (95% Confidence Interval)	Notes
Northern Indian (88)	ESKD	Cross sectional	184	569	OR, 1.44 (1.03 to 2.02)
AASK (27,67,72,91)	eGFR decline ESKD, death	Prospective	Approximately 700		HR, 2.1 (1.20 to 3.55)	No difference in baseline eGFR; CKD 3 and 4; 5 year follow up
Mexican (89)	ESKD	Cross sectional	110	125	OR, 2.05 (1.21 to 3.45)
ARIC (34)	Incident ESKD	Prospective	5715		HR, 1.76 (1.27 to 2.17)	30-year follow-up
South Indian (92)	CKD development or progression to ESKD	Prospective	170 with CKD; 222 with ESKD	202	HR, 2.9 (1.89-4.53) for CKD development; 1.8 1.19 to 2.83) for ESKD progression; 4.6 risk of death	70-month follow-up
Serbian (93)	Mortality in ESKD	Prospective	199		HR, 1.6 (1.1 to 2.3) and 2.1 (1.2 to 3.6) for overall mortality and CV mortality	8-year follow-up
Iranian (90)	ESKD	Cross sectional	136	137	OR, 3.04 (1.5 to 6.1)
CKiD (aged 1–16) (73)	CKD progression or dialysis	Prospective	674		HR, 1.94 (1.27 to 2.97)	Average at first follow-up visit 11.9 years; average 5.2 years follow-up
Black UK HIV (87)	Prevalent CKD	Cross sectional	687	2075	OR, 0.81 (0.61 to 1.04)	Majority had normal kidney function

OR, odds ratio; AASK, African American Study of Kidney Disease; HR, hazard ratio; ARIC, Atherosclerosis Risk in Communities; CV, cardiovascular; CKid, CKD in Children.

The effect of GSTM1 genotype on specific etiologies of CKD appears to differ. One recent study found a protective effect of GSTM1(0) in the development of Balkan endemic nephropathy (⁹⁵). Investigations in lupus nephritis have focused mainly on treatment, finding greater risk of nonkidney adverse drug reactions, including gastrointestinal upset, neutropenia, amenorrhea, and rash during cyclophosphamide treatment in GSTM1(0) genotypes (⁹⁶). Hydrocarbon-associated GN appears to be more common in persons with GSTM1 deletion (⁹⁷). Much work remains in delineating the exact role the GSTM1 deletion variant plays in the pathophysiology of CKD.

Risks Associated with GSTM1 Deletions in Advanced Age

GSTM1 deletions are associated with susceptibility to diseases of advanced age related to CKD, as in other age groups. Recently, Wang et al. (⁹⁸) conducted a meta-analysis of eight studies including 2031 individuals showed increased odds of Alzheimer disease with GSTM1 null genotype (OR, 1.34; 95% CI, 1.10 to 1.64). Although this study did not specifically analyze kidney disease phenotype, the associations between CKD and cognitive impairment are well reported (⁹⁹,¹⁰⁰). The GSTM1 null genotype is also associated with higher odds of age-related macular degeneration (¹⁰¹), another condition with well-documented associations with CKD (¹⁰²). As discussed earlier, GSTM1(0) increases susceptibility to multiple cancers, including solid tumors, for which increasing age is a primary risk factor. In multiple myeloma, the evidence for increased susceptibility with GSTM1 polymorphisms is mixed (^103–105), but available data seem to indicate that GSTM1 deletion is associated with poorer outcomes, such as disease-free progression and treatment response in patients with multiple myeloma.

The mixed association between GSTM1 genotype and HTN has been discussed above but, in the aging and longevity study in the Sirente Geographic Area (ilSIRENTE) cohort of 354 participants (mean±SD age, 85.8±4.8 years), GSTM1-null polymorphism was significantly associated with risk of HTN (OR, 2.25; 95% CI, 1.36 to 3.72) (¹⁰⁶). In 1-year-old mice (average life span of 2 years), deletion of Gstm1 did not result in any change in BP or kidney morphology at baseline; however, the researchers did not perform phenotyping beyond 1 year of age to determine its effect on BP or longevity in very old mice (²⁸).

Conclusion

In summary, GSTM1 plays a modifying role in many disease states across the life span (Figure 2). Although the upstream regulation of GSTM1 by Nrf2 has been defined, its downstream effect remains poorly understood. Furthermore, the relative contribution of GSTM1’s enzymatic function to limit oxidative stress versus the ASK1 inhibitory effect of GSTM1 in health and disease is unknown. Moreover, the evolutionary pressure leading to the major allele status of GSTM1 null allele that is associated with so many diseases and adverse outcomes across the life span remains an enigma. Future work in basic science and translational laboratories will be vital in defining these effects. In addition, granular epidemiologic work determining the specific effects of GSTM1 deletion and its relative frequencies among various racial and ethnic groups will be extremely valuable in the context of disparities in diagnosis and treatment of kidney disease. Delineation of the molecular and/or metabolic pathway regulated by GSTM1 has important therapeutic implications in kidney and other diseases across the life span in the context of precision and individualized medicine. These implications, once appropriately studied, may include specific dietary modifications (e.g., increasing cruciferous vegetable intake) or pharmacologic interventions (e.g., sulforaphane supplementation, miR-425-5p inhibitor). The potential for direct gene therapy is more difficult to predict; ongoing study will be critical.

Figure 2.: Risks associated with GSTM1 deletions across the life span. Graphical illustration of associations between the GSTM1 null allele and clinical outcomes across the life course. In pregnancy, GSTM1 deletion is associated with preeclampsia and gestational diabetes in the mother, and intrauterine growth restriction and prematurity of the fetus. Phenotypes associated with GSTM1 deletion in childhood include increased incidence of acute lymphocytic leukemia (ALL), increased incidence of type 1 diabetes mellitus (DM1), increased toxicity of chemotherapeutic agents, increased risk of vaso-occlusive crisis (VOC) in sickle cell disease (SCD), and increased rate of progression of CKD. In adulthood, GSTM1 deletion is associated with increased incidence of atherosclerotic cardiovascular disease (ASCVD), malignancy, type 2 diabetes mellitus (DM2), and CKD, and faster progression of CKD. In the elderly population, GSTM1 deletion is associated with increased odds of Alzheimer disease, age-related macular degeneration, cancer susceptibility, hypertension (HTN), and poor response to treatment of multiple myeloma (MM). Adapted from Creative Commons Attribution Share-Alike 3.0 image by Mohammed K. Jajjar.

Disclosures

Thu H. Le reports serving in an advisory or leadership role for AstraZeneca (paid advisory role); having consultancy agreements with Becton and Dickinson and Company; having ownership interest in Goldilocks; and receiving research funding from Renal Research Institute. The remaining author has nothing to disclose.

Funding

This work is supported, in part, by National Institute of Diabetes and Digestive and Kidney Diseases grants R01DK094907 and R01DK128677 (to T.H. Le).