Zhe Han

Histone lysine methyltransferases (KMTs) regulate chromatin states that control gene expression during development and disease. In the kidney, emerging evidence links KMT-dependent histone methylation to nephrogenesis, podocyte integrity, diabetic kidney disease, acute kidney injury, renal fibrosis, polycystic kidney disease, and renal cancer. Human genetic studies further support a developmental role for KMTs, as pathogenic variants in KMT2D, NSD1, EHMT1, and related chromatin regulators are associated with syndromic renal and urinary tract abnormalities. Mechanistic studies implicate EZH2, DOT1L, SETD2, G9a, SETDB1, SETD7, KMT2A, and SMYD2 in podocyte injury, tubular stress responses, and fibrotic remodeling. However, the renal cell-specific functions and relevant substrates of many KMTs remain incompletely defined. This review compares clinical associations, experimental KMT dependence, and locus-specific chromatin evidence across renal compartments. The synthesis identifies a central limitation: the renal effect of a KMT cannot be inferred from its associated histone mark alone, and beneficial inhibition in one setting may conflict with protective functions in another. We integrate representative mechanisms, evaluate the limits of experimental models, and outline priorities for human renal validation and cell-specific therapeutic development.

APOL1 risk variants are the strongest genetic determinants of HIV-associated nephropathy (HIVAN), yet the mechanisms linking inflammation to APOL1-mediated podocyte injury remain poorly understood because authentic patient-derived human disease models are lacking. Using urine-derived podocytes established from children with HIVAN and endogenous APOL1 reporter cell lines derived from these cells, we identified a previously unrecognized pathway of inflammatory, cathepsin-dependent APOL1 proteolysis. Endogenous APOL1 cleavage was detected in patient-derived podocytes, whereas reporter cell lines enabled the identification and functional characterization of N-terminal and C-terminal APOL1 fragments with distinct intracellular localization and pathogenic functions. The nuclear N-terminal fragment activated inflammatory transcriptional programs and promoted podocyte injury, whereas the membrane-associated C-terminal fragment mediated membrane toxicity and remained susceptible to pharmacologic inhibition by inaxaplin. Cathepsin S directly cleaved APOL1 in vitro, linking inflammatory signaling to APOL1 fragmentation. These findings identify inflammatory APOL1 proteolysis as a mechanism that partitions APOL1 toxicity into distinct pathogenic programs and nominate APOL1 processing as a therapeutic target for HIV-associated and other APOL1-mediated kidney diseases.

Introduction: Heart failure with preserved ejection fraction (HFpEF) is strongly associated with cardiometabolic comorbidities, including obesity, diabetes, hypertension, chronic kidney disease and aging, yet the mechanistic contribution of cellular senescence to HFpEF pathogenesis remains poorly defined. Methods and Results: To model clinically relevant HFpEF, we subjected p16-3MR mice to a novel chronic “four-hit” cardiovascular-kidney-metabolic stress regimen (10 months of a high-fat diet, low-dose streptozotocin, L-NAME, and aging). These mice developed a robust HFpEF phenotype characterized by left ventricular hypertrophy, impaired diastolic function (reduced E′/A′ and elevated E/E′), preserved ejection fraction, reduced −dP/dt, exercise intolerance, pulmonary congestion, and increased cardiac CD68⁺ macrophage infiltration. Cardiac proteomics identified 821 proteins significantly altered by four-hit stress. Selective genetic ablation of p16⁺ senescent cells using ganciclovir ameliorated HFpEF phenotypes, reduced cardiac p16 expression and inflammation, and normalized proteomic remodeling, without affecting body weight or glycemic status. Comparative network analysis of mouse and human HFpEF cardiac proteomes revealed highly concordant upstream regulatory networks, prominently involving cell-cycle control, DNA damage responses, and inflammatory signaling. Immunohistochemical analysis of human HFpEF cardiac biopsies confirmed increased p16, γH2AX, STING, IRF3, NF-κB p65, and CD68⁺ macrophages, mirroring the murine findings. The 4-Hit mice also developed chronic diabetic kidney disease with increased kidney inflammation, both of which were attenuated by Senolytic therapy. Mechanistically, the cGAS-STING (cyclic GMP-AMP synthase – stimulator of interferon genes) is activated in response to damaged DNA, which in turn activates the downstream immune responses, including NF-κB and interferons. Cross-species validation further demonstrated that combined metabolic stress impaired cardiac function and nephrocyte function in Drosophila. Cardiac and nephrocyte dysfunctions were independently rescued by cardiomyocyte-specific and nephrocyte-specific inhibition of the cGAS-STING pathway, respectively. In human iPSC-derived cardiomyocytes, irradiation and palmitate induced senescence, DNA damage sensing via ZBP1, and activation of the cGAS-STING-IRF3 signaling axis; ZBP1 knockdown or senolytic treatment suppressed this inflammatory axis. Conclusions: Across mouse, human, fly, and human iPSC models, our findings identify DNA damage–driven senescence and ZBP1–cGAS–STING signaling as conserved, causal mechanisms linking cardiovascular-kidney-metabolic comorbidities to HFpEF, highlighting senescence and innate immune pathways as promising therapeutic targets.

Cardiac arrhythmia leads to increased risks for stroke, heart failure, and cardiac arrest. Arrhythmic pathology is often rooted in the cardiac conduction system, but the mechanism is complex and not fully understood. For example, how metabolic diseases, like obesity and diabetes, increase the risk for cardiac arrhythmia. Glucagon regulates glucose production, mobilizes lipids from the fat body, and affects cardiac rate and rhythm, attributes of a likely key player. Drosophila is an established model to study metabolic diseases and cardiac arrhythmias. Since glucagon signaling is highly conserved, we used high-fat diet (HFD)-fed flies to study its effect on heart function. HFD led to increased heartbeat and an irregular rhythm. The HFD-fed flies showed increased levels of adipokinetic hormone (Akh), the functional equivalent to human glucagon. Both genetic reduction of Akh and eliminating the Akh-producing cells (APC) rescued HFD-induced arrhythmia, whereas heart rhythm was normal in Akh receptor mutants ( AkhR ^null ). Furthermore, we discovered a pair of cardiac neurons that express high levels of Akh receptor. These are located near the posterior heart, make synaptic connections at the heart muscle, and regulate heart rhythm. Altogether, this Akh signaling pathway provides new understanding of the regulatory mechanisms between metabolic disease and cardiac arrhythmia.

Cardiac arrhythmia leads to increased risks for stroke, heart failure, and cardiac arrest. Arrhythmic pathology is often rooted in the cardiac conduction system, but the mechanism is complex and not fully understood. For example, how metabolic diseases, like obesity and diabetes, increase the risk for cardiac arrhythmia. Glucagon regulates glucose production, mobilizes lipids from the fat body, and affects cardiac rate and rhythm, attributes of a likely key player. Drosophila is an established model to study metabolic diseases and cardiac arrhythmias. Since glucagon signaling is highly conserved, we used high-fat diet (HFD)-fed flies to study its effect on heart function. HFD led to increased heartbeat and an irregular rhythm. The HFD-fed flies showed increased levels of adipokinetic hormone (Akh), the functional equivalent to human glucagon. Both genetic reduction of Akh and eliminating the Akh producing cells (APC) rescued HFD-induced arrhythmia, whereas heart rhythm was normal in Akh receptor mutants (AkhRnull). Furthermore, we discovered a pair of cardiac neurons that express high levels of Akh receptor. These are located near the posterior heart, make synaptic connections at the heart muscle, and regulate heart rhythm. Altogether, this Akh signaling pathway provides new understanding of the regulatory mechanisms between metabolic disease and cardiac arrhythmia.

Chronic kidney disease is a major health issue and is gaining prevalence. Using a Drosophila model for chronic kidney disease, we show that a high-fat diet (HFD) disrupts the slit diaphragm filtration structure in nephrocytes, the fly functional equivalent of mammalian podocytes. The structural disruption resulted in reduced filtration function in the affected nephrocytes. We demonstrate that HFD activates the JAK-STAT pathway in nephrocytes, which has previously been linked to diabetic kidney disease. JAK-STAT activation was initiated by increased expression and release of the adipokine, Upd2, from the fat body. This leptin-like hormone is a known ligand of JAK-STAT. Both genetic and pharmacological inhibition of JAK-STAT restored nephrocyte HFD-associated dysfunction. Altogether, our study reveals the importance of the JAK-STAT signaling pathway in the adipose tissue−nephrocyte axis and its contribution to HFD-associated nephropathy. These findings open new avenues for intervention in treating diabetic nephropathy and chronic kidney disease.

N-terminal acetylation, catalyzed by N-terminal acetyltransferase (NAT) complexes, is one of the most prevalent protein modifications in eukaryotic cells, yet its role in heart development remains poorly understood. Here, we use Drosophila as an in vivo platform to investigate the functions of NAT complex components in cardiac development and congenital heart disease (CHD). Focusing on the NatA complex, we showed that cardiac-specific knockdown of each of its three subunits (Naa15-16, vnc, and san) led to developmental lethality, structural disorganization, fibrosis, and impaired cardiac function in Drosophila. Remarkably, human NAA16 completely rescued the cardiac defects in Naa15-16 silenced Drosophila, whereas a CHD-associated variant (NAA16-R70C) failed to do so, providing direct functional evidence of its pathogenicity. Together, these findings suggest the NatA complex as a critical regulator of heart development and provide functional validation linking variants in NatA complex genes to CHD. Further studies in mammalian models will be required to provide additional supporting evidence.

People carrying two APOL1 risk alleles (RA) – G1 or G2 – are at greater risk of developing human immunodeficiency virus (HIV)-associated nephropathy (HIVAN). However, it remains unclear whether the encoded protein(s) (APOL1-RA) and HIV-1 Nef interact to induce podocyte cell death. Here, we generated transgenic flies that express APOL1-G1 (derived from a child with HIVAN) and HIV-1 nef specifically in the nephrocytes, the fly equivalent of mammalian podocytes, and assessed their individual and combined effects on the nephrocyte filtration structure and function. We found that HIV-1 Nef acts in synergy with APOL1-G1, resulting in nephrocyte structural and functional defects, and that Nef exacerbates the organelle acidification defects and autophagy reduction induced by APOL1-G1. The synergy between HIV-1 Nef and APOL1-G1 is built on their joint effects on elevating endoplasmic reticulum (ER) stress, triggering nephrocyte dysfunction and, ultimately, cell death. Thus, we identified ER stress as the converging point for the synergy between HIV-1 Nef and APOL1-G1 in inducing nephrocyte cell death. Given the high similarity between Drosophila nephrocytes and human podocytes, our findings suggest ER stress as a new therapeutic target for HIV-1- and APOL1-associated nephropathies.